1348 lines
48 KiB
Go
1348 lines
48 KiB
Go
// Copyright 2021 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package runtime
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import (
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"internal/cpu"
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"internal/goexperiment"
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"runtime/internal/atomic"
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"unsafe"
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)
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const (
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// gcGoalUtilization is the goal CPU utilization for
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// marking as a fraction of GOMAXPROCS.
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gcGoalUtilization = goexperiment.PacerRedesignInt*gcBackgroundUtilization +
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(1-goexperiment.PacerRedesignInt)*(gcBackgroundUtilization+0.05)
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// gcBackgroundUtilization is the fixed CPU utilization for background
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// marking. It must be <= gcGoalUtilization. The difference between
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// gcGoalUtilization and gcBackgroundUtilization will be made up by
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// mark assists. The scheduler will aim to use within 50% of this
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// goal.
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//
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// Setting this to < gcGoalUtilization avoids saturating the trigger
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// feedback controller when there are no assists, which allows it to
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// better control CPU and heap growth. However, the larger the gap,
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// the more mutator assists are expected to happen, which impact
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// mutator latency.
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//
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// If goexperiment.PacerRedesign, the trigger feedback controller
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// is replaced with an estimate of the mark/cons ratio that doesn't
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// have the same saturation issues, so this is set equal to
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// gcGoalUtilization.
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gcBackgroundUtilization = 0.25
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// gcCreditSlack is the amount of scan work credit that can
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// accumulate locally before updating gcController.heapScanWork and,
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// optionally, gcController.bgScanCredit. Lower values give a more
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// accurate assist ratio and make it more likely that assists will
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// successfully steal background credit. Higher values reduce memory
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// contention.
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gcCreditSlack = 2000
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// gcAssistTimeSlack is the nanoseconds of mutator assist time that
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// can accumulate on a P before updating gcController.assistTime.
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gcAssistTimeSlack = 5000
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// gcOverAssistWork determines how many extra units of scan work a GC
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// assist does when an assist happens. This amortizes the cost of an
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// assist by pre-paying for this many bytes of future allocations.
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gcOverAssistWork = 64 << 10
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// defaultHeapMinimum is the value of heapMinimum for GOGC==100.
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defaultHeapMinimum = (goexperiment.HeapMinimum512KiBInt)*(512<<10) +
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(1-goexperiment.HeapMinimum512KiBInt)*(4<<20)
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// scannableStackSizeSlack is the bytes of stack space allocated or freed
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// that can accumulate on a P before updating gcController.stackSize.
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scannableStackSizeSlack = 8 << 10
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)
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func init() {
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if offset := unsafe.Offsetof(gcController.heapLive); offset%8 != 0 {
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println(offset)
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throw("gcController.heapLive not aligned to 8 bytes")
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}
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}
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// gcController implements the GC pacing controller that determines
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// when to trigger concurrent garbage collection and how much marking
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// work to do in mutator assists and background marking.
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//
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// It uses a feedback control algorithm to adjust the gcController.trigger
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// trigger based on the heap growth and GC CPU utilization each cycle.
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// This algorithm optimizes for heap growth to match GOGC and for CPU
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// utilization between assist and background marking to be 25% of
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// GOMAXPROCS. The high-level design of this algorithm is documented
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// at https://golang.org/s/go15gcpacing.
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//
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// All fields of gcController are used only during a single mark
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// cycle.
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var gcController gcControllerState
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type gcControllerState struct {
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// Initialized from GOGC. GOGC=off means no GC.
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gcPercent atomic.Int32
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_ uint32 // padding so following 64-bit values are 8-byte aligned
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// heapMinimum is the minimum heap size at which to trigger GC.
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// For small heaps, this overrides the usual GOGC*live set rule.
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//
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// When there is a very small live set but a lot of allocation, simply
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// collecting when the heap reaches GOGC*live results in many GC
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// cycles and high total per-GC overhead. This minimum amortizes this
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// per-GC overhead while keeping the heap reasonably small.
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//
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// During initialization this is set to 4MB*GOGC/100. In the case of
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// GOGC==0, this will set heapMinimum to 0, resulting in constant
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// collection even when the heap size is small, which is useful for
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// debugging.
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heapMinimum uint64
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// triggerRatio is the heap growth ratio that triggers marking.
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//
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// E.g., if this is 0.6, then GC should start when the live
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// heap has reached 1.6 times the heap size marked by the
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// previous cycle. This should be ≤ GOGC/100 so the trigger
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// heap size is less than the goal heap size. This is set
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// during mark termination for the next cycle's trigger.
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//
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// Protected by mheap_.lock or a STW.
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//
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// Used if !goexperiment.PacerRedesign.
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triggerRatio float64
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// trigger is the heap size that triggers marking.
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//
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// When heapLive ≥ trigger, the mark phase will start.
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// This is also the heap size by which proportional sweeping
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// must be complete.
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//
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// This is computed from triggerRatio during mark termination
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// for the next cycle's trigger.
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//
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// Protected by mheap_.lock or a STW.
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trigger uint64
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// consMark is the estimated per-CPU consMark ratio for the application.
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//
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// It represents the ratio between the application's allocation
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// rate, as bytes allocated per CPU-time, and the GC's scan rate,
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// as bytes scanned per CPU-time.
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// The units of this ratio are (B / cpu-ns) / (B / cpu-ns).
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//
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// At a high level, this value is computed as the bytes of memory
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// allocated (cons) per unit of scan work completed (mark) in a GC
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// cycle, divided by the CPU time spent on each activity.
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//
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// Updated at the end of each GC cycle, in endCycle.
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//
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// For goexperiment.PacerRedesign.
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consMark float64
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// consMarkController holds the state for the mark-cons ratio
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// estimation over time.
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//
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// Its purpose is to smooth out noisiness in the computation of
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// consMark; see consMark for details.
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//
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// For goexperiment.PacerRedesign.
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consMarkController piController
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_ uint32 // Padding for atomics on 32-bit platforms.
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// heapGoal is the goal heapLive for when next GC ends.
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// Set to ^uint64(0) if disabled.
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//
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// Read and written atomically, unless the world is stopped.
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heapGoal uint64
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// lastHeapGoal is the value of heapGoal for the previous GC.
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// Note that this is distinct from the last value heapGoal had,
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// because it could change if e.g. gcPercent changes.
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//
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// Read and written with the world stopped or with mheap_.lock held.
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lastHeapGoal uint64
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// heapLive is the number of bytes considered live by the GC.
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// That is: retained by the most recent GC plus allocated
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// since then. heapLive ≤ memstats.heapAlloc, since heapAlloc includes
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// unmarked objects that have not yet been swept (and hence goes up as we
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// allocate and down as we sweep) while heapLive excludes these
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// objects (and hence only goes up between GCs).
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//
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// This is updated atomically without locking. To reduce
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// contention, this is updated only when obtaining a span from
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// an mcentral and at this point it counts all of the
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// unallocated slots in that span (which will be allocated
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// before that mcache obtains another span from that
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// mcentral). Hence, it slightly overestimates the "true" live
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// heap size. It's better to overestimate than to
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// underestimate because 1) this triggers the GC earlier than
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// necessary rather than potentially too late and 2) this
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// leads to a conservative GC rate rather than a GC rate that
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// is potentially too low.
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//
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// Reads should likewise be atomic (or during STW).
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//
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// Whenever this is updated, call traceHeapAlloc() and
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// this gcControllerState's revise() method.
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heapLive uint64
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// heapScan is the number of bytes of "scannable" heap. This
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// is the live heap (as counted by heapLive), but omitting
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// no-scan objects and no-scan tails of objects.
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//
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// For !goexperiment.PacerRedesign: Whenever this is updated,
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// call this gcControllerState's revise() method. It is read
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// and written atomically or with the world stopped.
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//
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// For goexperiment.PacerRedesign: This value is fixed at the
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// start of a GC cycle, so during a GC cycle it is safe to
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// read without atomics, and it represents the maximum scannable
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// heap.
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heapScan uint64
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// lastHeapScan is the number of bytes of heap that were scanned
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// last GC cycle. It is the same as heapMarked, but only
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// includes the "scannable" parts of objects.
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//
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// Updated when the world is stopped.
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lastHeapScan uint64
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// stackScan is a snapshot of scannableStackSize taken at each GC
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// STW pause and is used in pacing decisions.
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//
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// Updated only while the world is stopped.
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stackScan uint64
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// scannableStackSize is the amount of allocated goroutine stack space in
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// use by goroutines.
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//
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// This number tracks allocated goroutine stack space rather than used
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// goroutine stack space (i.e. what is actually scanned) because used
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// goroutine stack space is much harder to measure cheaply. By using
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// allocated space, we make an overestimate; this is OK, it's better
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// to conservatively overcount than undercount.
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//
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// Read and updated atomically.
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scannableStackSize uint64
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// globalsScan is the total amount of global variable space
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// that is scannable.
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//
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// Read and updated atomically.
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globalsScan uint64
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// heapMarked is the number of bytes marked by the previous
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// GC. After mark termination, heapLive == heapMarked, but
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// unlike heapLive, heapMarked does not change until the
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// next mark termination.
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heapMarked uint64
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// heapScanWork is the total heap scan work performed this cycle.
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// stackScanWork is the total stack scan work performed this cycle.
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// globalsScanWork is the total globals scan work performed this cycle.
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//
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// These are updated atomically during the cycle. Updates occur in
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// bounded batches, since they are both written and read
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// throughout the cycle. At the end of the cycle, heapScanWork is how
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// much of the retained heap is scannable.
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//
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// Currently these are measured in bytes. For most uses, this is an
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// opaque unit of work, but for estimation the definition is important.
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//
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// Note that stackScanWork includes all allocated space, not just the
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// size of the stack itself, mirroring stackSize.
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//
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// For !goexperiment.PacerRedesign, stackScanWork and globalsScanWork
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// are always zero.
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heapScanWork atomic.Int64
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stackScanWork atomic.Int64
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globalsScanWork atomic.Int64
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// bgScanCredit is the scan work credit accumulated by the
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// concurrent background scan. This credit is accumulated by
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// the background scan and stolen by mutator assists. This is
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// updated atomically. Updates occur in bounded batches, since
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// it is both written and read throughout the cycle.
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bgScanCredit int64
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// assistTime is the nanoseconds spent in mutator assists
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// during this cycle. This is updated atomically. Updates
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// occur in bounded batches, since it is both written and read
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// throughout the cycle.
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assistTime int64
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// dedicatedMarkTime is the nanoseconds spent in dedicated
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// mark workers during this cycle. This is updated atomically
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// at the end of the concurrent mark phase.
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dedicatedMarkTime int64
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// fractionalMarkTime is the nanoseconds spent in the
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// fractional mark worker during this cycle. This is updated
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// atomically throughout the cycle and will be up-to-date if
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// the fractional mark worker is not currently running.
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fractionalMarkTime int64
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// idleMarkTime is the nanoseconds spent in idle marking
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// during this cycle. This is updated atomically throughout
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// the cycle.
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idleMarkTime int64
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// markStartTime is the absolute start time in nanoseconds
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// that assists and background mark workers started.
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markStartTime int64
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// dedicatedMarkWorkersNeeded is the number of dedicated mark
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// workers that need to be started. This is computed at the
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// beginning of each cycle and decremented atomically as
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// dedicated mark workers get started.
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dedicatedMarkWorkersNeeded int64
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// assistWorkPerByte is the ratio of scan work to allocated
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// bytes that should be performed by mutator assists. This is
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// computed at the beginning of each cycle and updated every
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// time heapScan is updated.
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assistWorkPerByte atomic.Float64
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// assistBytesPerWork is 1/assistWorkPerByte.
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//
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// Note that because this is read and written independently
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// from assistWorkPerByte users may notice a skew between
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// the two values, and such a state should be safe.
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assistBytesPerWork atomic.Float64
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// fractionalUtilizationGoal is the fraction of wall clock
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// time that should be spent in the fractional mark worker on
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// each P that isn't running a dedicated worker.
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//
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// For example, if the utilization goal is 25% and there are
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// no dedicated workers, this will be 0.25. If the goal is
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// 25%, there is one dedicated worker, and GOMAXPROCS is 5,
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// this will be 0.05 to make up the missing 5%.
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//
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// If this is zero, no fractional workers are needed.
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fractionalUtilizationGoal float64
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// test indicates that this is a test-only copy of gcControllerState.
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test bool
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_ cpu.CacheLinePad
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}
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func (c *gcControllerState) init(gcPercent int32) {
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c.heapMinimum = defaultHeapMinimum
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if goexperiment.PacerRedesign {
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c.consMarkController = piController{
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// Tuned first via the Ziegler-Nichols process in simulation,
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// then the integral time was manually tuned against real-world
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// applications to deal with noisiness in the measured cons/mark
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// ratio.
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kp: 0.9,
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ti: 4.0,
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// Set a high reset time in GC cycles.
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// This is inversely proportional to the rate at which we
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// accumulate error from clipping. By making this very high
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// we make the accumulation slow. In general, clipping is
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// OK in our situation, hence the choice.
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//
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// Tune this if we get unintended effects from clipping for
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// a long time.
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tt: 1000,
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min: -1000,
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max: 1000,
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}
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} else {
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// Set a reasonable initial GC trigger.
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c.triggerRatio = 7 / 8.0
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// Fake a heapMarked value so it looks like a trigger at
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// heapMinimum is the appropriate growth from heapMarked.
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// This will go into computing the initial GC goal.
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c.heapMarked = uint64(float64(c.heapMinimum) / (1 + c.triggerRatio))
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}
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// This will also compute and set the GC trigger and goal.
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c.setGCPercent(gcPercent)
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}
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// startCycle resets the GC controller's state and computes estimates
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// for a new GC cycle. The caller must hold worldsema and the world
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// must be stopped.
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func (c *gcControllerState) startCycle(markStartTime int64, procs int) {
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c.heapScanWork.Store(0)
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c.stackScanWork.Store(0)
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c.globalsScanWork.Store(0)
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c.bgScanCredit = 0
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c.assistTime = 0
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c.dedicatedMarkTime = 0
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c.fractionalMarkTime = 0
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c.idleMarkTime = 0
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c.markStartTime = markStartTime
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c.stackScan = atomic.Load64(&c.scannableStackSize)
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// Ensure that the heap goal is at least a little larger than
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// the current live heap size. This may not be the case if GC
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// start is delayed or if the allocation that pushed gcController.heapLive
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// over trigger is large or if the trigger is really close to
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// GOGC. Assist is proportional to this distance, so enforce a
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// minimum distance, even if it means going over the GOGC goal
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// by a tiny bit.
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if goexperiment.PacerRedesign {
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if c.heapGoal < c.heapLive+64<<10 {
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c.heapGoal = c.heapLive + 64<<10
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}
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} else {
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if c.heapGoal < c.heapLive+1<<20 {
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c.heapGoal = c.heapLive + 1<<20
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}
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}
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// Compute the background mark utilization goal. In general,
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// this may not come out exactly. We round the number of
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// dedicated workers so that the utilization is closest to
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// 25%. For small GOMAXPROCS, this would introduce too much
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// error, so we add fractional workers in that case.
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totalUtilizationGoal := float64(procs) * gcBackgroundUtilization
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c.dedicatedMarkWorkersNeeded = int64(totalUtilizationGoal + 0.5)
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utilError := float64(c.dedicatedMarkWorkersNeeded)/totalUtilizationGoal - 1
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const maxUtilError = 0.3
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if utilError < -maxUtilError || utilError > maxUtilError {
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// Rounding put us more than 30% off our goal. With
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// gcBackgroundUtilization of 25%, this happens for
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// GOMAXPROCS<=3 or GOMAXPROCS=6. Enable fractional
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// workers to compensate.
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if float64(c.dedicatedMarkWorkersNeeded) > totalUtilizationGoal {
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// Too many dedicated workers.
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c.dedicatedMarkWorkersNeeded--
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}
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c.fractionalUtilizationGoal = (totalUtilizationGoal - float64(c.dedicatedMarkWorkersNeeded)) / float64(procs)
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} else {
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c.fractionalUtilizationGoal = 0
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}
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// In STW mode, we just want dedicated workers.
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if debug.gcstoptheworld > 0 {
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c.dedicatedMarkWorkersNeeded = int64(procs)
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c.fractionalUtilizationGoal = 0
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}
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// Clear per-P state
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for _, p := range allp {
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p.gcAssistTime = 0
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p.gcFractionalMarkTime = 0
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}
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// Compute initial values for controls that are updated
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// throughout the cycle.
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c.revise()
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if debug.gcpacertrace > 0 {
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assistRatio := c.assistWorkPerByte.Load()
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print("pacer: assist ratio=", assistRatio,
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" (scan ", gcController.heapScan>>20, " MB in ",
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work.initialHeapLive>>20, "->",
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c.heapGoal>>20, " MB)",
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" workers=", c.dedicatedMarkWorkersNeeded,
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"+", c.fractionalUtilizationGoal, "\n")
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}
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}
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// revise updates the assist ratio during the GC cycle to account for
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// improved estimates. This should be called whenever gcController.heapScan,
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// gcController.heapLive, or gcController.heapGoal is updated. It is safe to
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// call concurrently, but it may race with other calls to revise.
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//
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// The result of this race is that the two assist ratio values may not line
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// up or may be stale. In practice this is OK because the assist ratio
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// moves slowly throughout a GC cycle, and the assist ratio is a best-effort
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// heuristic anyway. Furthermore, no part of the heuristic depends on
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// the two assist ratio values being exact reciprocals of one another, since
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// the two values are used to convert values from different sources.
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//
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// The worst case result of this raciness is that we may miss a larger shift
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// in the ratio (say, if we decide to pace more aggressively against the
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// hard heap goal) but even this "hard goal" is best-effort (see #40460).
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// The dedicated GC should ensure we don't exceed the hard goal by too much
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// in the rare case we do exceed it.
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//
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// It should only be called when gcBlackenEnabled != 0 (because this
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// is when assists are enabled and the necessary statistics are
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// available).
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func (c *gcControllerState) revise() {
|
|
gcPercent := c.gcPercent.Load()
|
|
if gcPercent < 0 {
|
|
// If GC is disabled but we're running a forced GC,
|
|
// act like GOGC is huge for the below calculations.
|
|
gcPercent = 100000
|
|
}
|
|
live := atomic.Load64(&c.heapLive)
|
|
scan := atomic.Load64(&c.heapScan)
|
|
work := c.heapScanWork.Load() + c.stackScanWork.Load() + c.globalsScanWork.Load()
|
|
|
|
// Assume we're under the soft goal. Pace GC to complete at
|
|
// heapGoal assuming the heap is in steady-state.
|
|
heapGoal := int64(atomic.Load64(&c.heapGoal))
|
|
|
|
var scanWorkExpected int64
|
|
if goexperiment.PacerRedesign {
|
|
// The expected scan work is computed as the amount of bytes scanned last
|
|
// GC cycle, plus our estimate of stacks and globals work for this cycle.
|
|
scanWorkExpected = int64(c.lastHeapScan + c.stackScan + c.globalsScan)
|
|
|
|
// maxScanWork is a worst-case estimate of the amount of scan work that
|
|
// needs to be performed in this GC cycle. Specifically, it represents
|
|
// the case where *all* scannable memory turns out to be live.
|
|
maxScanWork := int64(scan + c.stackScan + c.globalsScan)
|
|
if work > scanWorkExpected {
|
|
// We've already done more scan work than expected. Because our expectation
|
|
// is based on a steady-state scannable heap size, we assume this means our
|
|
// heap is growing. Compute a new heap goal that takes our existing runway
|
|
// computed for scanWorkExpected and extrapolates it to maxScanWork, the worst-case
|
|
// scan work. This keeps our assist ratio stable if the heap continues to grow.
|
|
//
|
|
// The effect of this mechanism is that assists stay flat in the face of heap
|
|
// growths. It's OK to use more memory this cycle to scan all the live heap,
|
|
// because the next GC cycle is inevitably going to use *at least* that much
|
|
// memory anyway.
|
|
extHeapGoal := int64(float64(heapGoal-int64(c.trigger))/float64(scanWorkExpected)*float64(maxScanWork)) + int64(c.trigger)
|
|
scanWorkExpected = maxScanWork
|
|
|
|
// hardGoal is a hard limit on the amount that we're willing to push back the
|
|
// heap goal, and that's twice the heap goal (i.e. if GOGC=100 and the heap and/or
|
|
// stacks and/or globals grow to twice their size, this limits the current GC cycle's
|
|
// growth to 4x the original live heap's size).
|
|
//
|
|
// This maintains the invariant that we use no more memory than the next GC cycle
|
|
// will anyway.
|
|
hardGoal := int64((1.0 + float64(gcPercent)/100.0) * float64(heapGoal))
|
|
if extHeapGoal > hardGoal {
|
|
extHeapGoal = hardGoal
|
|
}
|
|
heapGoal = extHeapGoal
|
|
}
|
|
if int64(live) > heapGoal {
|
|
// We're already past our heap goal, even the extrapolated one.
|
|
// Leave ourselves some extra runway, so in the worst case we
|
|
// finish by that point.
|
|
const maxOvershoot = 1.1
|
|
heapGoal = int64(float64(heapGoal) * maxOvershoot)
|
|
|
|
// Compute the upper bound on the scan work remaining.
|
|
scanWorkExpected = maxScanWork
|
|
}
|
|
} else {
|
|
// Compute the expected scan work remaining.
|
|
//
|
|
// This is estimated based on the expected
|
|
// steady-state scannable heap. For example, with
|
|
// GOGC=100, only half of the scannable heap is
|
|
// expected to be live, so that's what we target.
|
|
//
|
|
// (This is a float calculation to avoid overflowing on
|
|
// 100*heapScan.)
|
|
scanWorkExpected = int64(float64(scan) * 100 / float64(100+gcPercent))
|
|
if int64(live) > heapGoal || work > scanWorkExpected {
|
|
// We're past the soft goal, or we've already done more scan
|
|
// work than we expected. Pace GC so that in the worst case it
|
|
// will complete by the hard goal.
|
|
const maxOvershoot = 1.1
|
|
heapGoal = int64(float64(heapGoal) * maxOvershoot)
|
|
|
|
// Compute the upper bound on the scan work remaining.
|
|
scanWorkExpected = int64(scan)
|
|
}
|
|
}
|
|
|
|
// Compute the remaining scan work estimate.
|
|
//
|
|
// Note that we currently count allocations during GC as both
|
|
// scannable heap (heapScan) and scan work completed
|
|
// (scanWork), so allocation will change this difference
|
|
// slowly in the soft regime and not at all in the hard
|
|
// regime.
|
|
scanWorkRemaining := scanWorkExpected - work
|
|
if scanWorkRemaining < 1000 {
|
|
// We set a somewhat arbitrary lower bound on
|
|
// remaining scan work since if we aim a little high,
|
|
// we can miss by a little.
|
|
//
|
|
// We *do* need to enforce that this is at least 1,
|
|
// since marking is racy and double-scanning objects
|
|
// may legitimately make the remaining scan work
|
|
// negative, even in the hard goal regime.
|
|
scanWorkRemaining = 1000
|
|
}
|
|
|
|
// Compute the heap distance remaining.
|
|
heapRemaining := heapGoal - int64(live)
|
|
if heapRemaining <= 0 {
|
|
// This shouldn't happen, but if it does, avoid
|
|
// dividing by zero or setting the assist negative.
|
|
heapRemaining = 1
|
|
}
|
|
|
|
// Compute the mutator assist ratio so by the time the mutator
|
|
// allocates the remaining heap bytes up to heapGoal, it will
|
|
// have done (or stolen) the remaining amount of scan work.
|
|
// Note that the assist ratio values are updated atomically
|
|
// but not together. This means there may be some degree of
|
|
// skew between the two values. This is generally OK as the
|
|
// values shift relatively slowly over the course of a GC
|
|
// cycle.
|
|
assistWorkPerByte := float64(scanWorkRemaining) / float64(heapRemaining)
|
|
assistBytesPerWork := float64(heapRemaining) / float64(scanWorkRemaining)
|
|
c.assistWorkPerByte.Store(assistWorkPerByte)
|
|
c.assistBytesPerWork.Store(assistBytesPerWork)
|
|
}
|
|
|
|
// endCycle computes the trigger ratio (!goexperiment.PacerRedesign)
|
|
// or the consMark estimate (goexperiment.PacerRedesign) for the next cycle.
|
|
// Returns the trigger ratio if application, or 0 (goexperiment.PacerRedesign).
|
|
// userForced indicates whether the current GC cycle was forced
|
|
// by the application.
|
|
func (c *gcControllerState) endCycle(now int64, procs int, userForced bool) float64 {
|
|
// Record last heap goal for the scavenger.
|
|
// We'll be updating the heap goal soon.
|
|
gcController.lastHeapGoal = gcController.heapGoal
|
|
|
|
// Compute the duration of time for which assists were turned on.
|
|
assistDuration := now - c.markStartTime
|
|
|
|
// Assume background mark hit its utilization goal.
|
|
utilization := gcBackgroundUtilization
|
|
// Add assist utilization; avoid divide by zero.
|
|
if assistDuration > 0 {
|
|
utilization += float64(c.assistTime) / float64(assistDuration*int64(procs))
|
|
}
|
|
|
|
if goexperiment.PacerRedesign {
|
|
if c.heapLive <= c.trigger {
|
|
// Shouldn't happen, but let's be very safe about this in case the
|
|
// GC is somehow extremely short.
|
|
//
|
|
// In this case though, the only reasonable value for c.heapLive-c.trigger
|
|
// would be 0, which isn't really all that useful, i.e. the GC was so short
|
|
// that it didn't matter.
|
|
//
|
|
// Ignore this case and don't update anything.
|
|
return 0
|
|
}
|
|
idleUtilization := 0.0
|
|
if assistDuration > 0 {
|
|
idleUtilization = float64(c.idleMarkTime) / float64(assistDuration*int64(procs))
|
|
}
|
|
// Determine the cons/mark ratio.
|
|
//
|
|
// The units we want for the numerator and denominator are both B / cpu-ns.
|
|
// We get this by taking the bytes allocated or scanned, and divide by the amount of
|
|
// CPU time it took for those operations. For allocations, that CPU time is
|
|
//
|
|
// assistDuration * procs * (1 - utilization)
|
|
//
|
|
// Where utilization includes just background GC workers and assists. It does *not*
|
|
// include idle GC work time, because in theory the mutator is free to take that at
|
|
// any point.
|
|
//
|
|
// For scanning, that CPU time is
|
|
//
|
|
// assistDuration * procs * (utilization + idleUtilization)
|
|
//
|
|
// In this case, we *include* idle utilization, because that is additional CPU time that the
|
|
// the GC had available to it.
|
|
//
|
|
// In effect, idle GC time is sort of double-counted here, but it's very weird compared
|
|
// to other kinds of GC work, because of how fluid it is. Namely, because the mutator is
|
|
// *always* free to take it.
|
|
//
|
|
// So this calculation is really:
|
|
// (heapLive-trigger) / (assistDuration * procs * (1-utilization)) /
|
|
// (scanWork) / (assistDuration * procs * (utilization+idleUtilization)
|
|
//
|
|
// Note that because we only care about the ratio, assistDuration and procs cancel out.
|
|
scanWork := c.heapScanWork.Load() + c.stackScanWork.Load() + c.globalsScanWork.Load()
|
|
currentConsMark := (float64(c.heapLive-c.trigger) * (utilization + idleUtilization)) /
|
|
(float64(scanWork) * (1 - utilization))
|
|
|
|
// Update cons/mark controller. The time period for this is 1 GC cycle.
|
|
//
|
|
// This use of a PI controller might seem strange. So, here's an explanation:
|
|
//
|
|
// currentConsMark represents the consMark we *should've* had to be perfectly
|
|
// on-target for this cycle. Given that we assume the next GC will be like this
|
|
// one in the steady-state, it stands to reason that we should just pick that
|
|
// as our next consMark. In practice, however, currentConsMark is too noisy:
|
|
// we're going to be wildly off-target in each GC cycle if we do that.
|
|
//
|
|
// What we do instead is make a long-term assumption: there is some steady-state
|
|
// consMark value, but it's obscured by noise. By constantly shooting for this
|
|
// noisy-but-perfect consMark value, the controller will bounce around a bit,
|
|
// but its average behavior, in aggregate, should be less noisy and closer to
|
|
// the true long-term consMark value, provided its tuned to be slightly overdamped.
|
|
var ok bool
|
|
oldConsMark := c.consMark
|
|
c.consMark, ok = c.consMarkController.next(c.consMark, currentConsMark, 1.0)
|
|
if !ok {
|
|
// The error spiraled out of control. This is incredibly unlikely seeing
|
|
// as this controller is essentially just a smoothing function, but it might
|
|
// mean that something went very wrong with how currentConsMark was calculated.
|
|
// Just reset consMark and keep going.
|
|
c.consMark = 0
|
|
}
|
|
|
|
if debug.gcpacertrace > 0 {
|
|
printlock()
|
|
goal := gcGoalUtilization * 100
|
|
print("pacer: ", int(utilization*100), "% CPU (", int(goal), " exp.) for ")
|
|
print(c.heapScanWork.Load(), "+", c.stackScanWork.Load(), "+", c.globalsScanWork.Load(), " B work (", c.lastHeapScan+c.stackScan+c.globalsScan, " B exp.) ")
|
|
print("in ", c.trigger, " B -> ", c.heapLive, " B (∆goal ", int64(c.heapLive)-int64(c.heapGoal), ", cons/mark ", oldConsMark, ")")
|
|
if !ok {
|
|
print("[controller reset]")
|
|
}
|
|
println()
|
|
printunlock()
|
|
}
|
|
return 0
|
|
}
|
|
|
|
// !goexperiment.PacerRedesign below.
|
|
|
|
if userForced {
|
|
// Forced GC means this cycle didn't start at the
|
|
// trigger, so where it finished isn't good
|
|
// information about how to adjust the trigger.
|
|
// Just leave it where it is.
|
|
return c.triggerRatio
|
|
}
|
|
|
|
// Proportional response gain for the trigger controller. Must
|
|
// be in [0, 1]. Lower values smooth out transient effects but
|
|
// take longer to respond to phase changes. Higher values
|
|
// react to phase changes quickly, but are more affected by
|
|
// transient changes. Values near 1 may be unstable.
|
|
const triggerGain = 0.5
|
|
|
|
// Compute next cycle trigger ratio. First, this computes the
|
|
// "error" for this cycle; that is, how far off the trigger
|
|
// was from what it should have been, accounting for both heap
|
|
// growth and GC CPU utilization. We compute the actual heap
|
|
// growth during this cycle and scale that by how far off from
|
|
// the goal CPU utilization we were (to estimate the heap
|
|
// growth if we had the desired CPU utilization). The
|
|
// difference between this estimate and the GOGC-based goal
|
|
// heap growth is the error.
|
|
goalGrowthRatio := c.effectiveGrowthRatio()
|
|
actualGrowthRatio := float64(c.heapLive)/float64(c.heapMarked) - 1
|
|
triggerError := goalGrowthRatio - c.triggerRatio - utilization/gcGoalUtilization*(actualGrowthRatio-c.triggerRatio)
|
|
|
|
// Finally, we adjust the trigger for next time by this error,
|
|
// damped by the proportional gain.
|
|
triggerRatio := c.triggerRatio + triggerGain*triggerError
|
|
|
|
if debug.gcpacertrace > 0 {
|
|
// Print controller state in terms of the design
|
|
// document.
|
|
H_m_prev := c.heapMarked
|
|
h_t := c.triggerRatio
|
|
H_T := c.trigger
|
|
h_a := actualGrowthRatio
|
|
H_a := c.heapLive
|
|
h_g := goalGrowthRatio
|
|
H_g := int64(float64(H_m_prev) * (1 + h_g))
|
|
u_a := utilization
|
|
u_g := gcGoalUtilization
|
|
W_a := c.heapScanWork.Load()
|
|
print("pacer: H_m_prev=", H_m_prev,
|
|
" h_t=", h_t, " H_T=", H_T,
|
|
" h_a=", h_a, " H_a=", H_a,
|
|
" h_g=", h_g, " H_g=", H_g,
|
|
" u_a=", u_a, " u_g=", u_g,
|
|
" W_a=", W_a,
|
|
" goalΔ=", goalGrowthRatio-h_t,
|
|
" actualΔ=", h_a-h_t,
|
|
" u_a/u_g=", u_a/u_g,
|
|
"\n")
|
|
}
|
|
|
|
return triggerRatio
|
|
}
|
|
|
|
// enlistWorker encourages another dedicated mark worker to start on
|
|
// another P if there are spare worker slots. It is used by putfull
|
|
// when more work is made available.
|
|
//
|
|
//go:nowritebarrier
|
|
func (c *gcControllerState) enlistWorker() {
|
|
// If there are idle Ps, wake one so it will run an idle worker.
|
|
// NOTE: This is suspected of causing deadlocks. See golang.org/issue/19112.
|
|
//
|
|
// if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 {
|
|
// wakep()
|
|
// return
|
|
// }
|
|
|
|
// There are no idle Ps. If we need more dedicated workers,
|
|
// try to preempt a running P so it will switch to a worker.
|
|
if c.dedicatedMarkWorkersNeeded <= 0 {
|
|
return
|
|
}
|
|
// Pick a random other P to preempt.
|
|
if gomaxprocs <= 1 {
|
|
return
|
|
}
|
|
gp := getg()
|
|
if gp == nil || gp.m == nil || gp.m.p == 0 {
|
|
return
|
|
}
|
|
myID := gp.m.p.ptr().id
|
|
for tries := 0; tries < 5; tries++ {
|
|
id := int32(fastrandn(uint32(gomaxprocs - 1)))
|
|
if id >= myID {
|
|
id++
|
|
}
|
|
p := allp[id]
|
|
if p.status != _Prunning {
|
|
continue
|
|
}
|
|
if preemptone(p) {
|
|
return
|
|
}
|
|
}
|
|
}
|
|
|
|
// findRunnableGCWorker returns a background mark worker for _p_ if it
|
|
// should be run. This must only be called when gcBlackenEnabled != 0.
|
|
func (c *gcControllerState) findRunnableGCWorker(_p_ *p) *g {
|
|
if gcBlackenEnabled == 0 {
|
|
throw("gcControllerState.findRunnable: blackening not enabled")
|
|
}
|
|
|
|
if !gcMarkWorkAvailable(_p_) {
|
|
// No work to be done right now. This can happen at
|
|
// the end of the mark phase when there are still
|
|
// assists tapering off. Don't bother running a worker
|
|
// now because it'll just return immediately.
|
|
return nil
|
|
}
|
|
|
|
// Grab a worker before we commit to running below.
|
|
node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
|
|
if node == nil {
|
|
// There is at least one worker per P, so normally there are
|
|
// enough workers to run on all Ps, if necessary. However, once
|
|
// a worker enters gcMarkDone it may park without rejoining the
|
|
// pool, thus freeing a P with no corresponding worker.
|
|
// gcMarkDone never depends on another worker doing work, so it
|
|
// is safe to simply do nothing here.
|
|
//
|
|
// If gcMarkDone bails out without completing the mark phase,
|
|
// it will always do so with queued global work. Thus, that P
|
|
// will be immediately eligible to re-run the worker G it was
|
|
// just using, ensuring work can complete.
|
|
return nil
|
|
}
|
|
|
|
decIfPositive := func(ptr *int64) bool {
|
|
for {
|
|
v := atomic.Loadint64(ptr)
|
|
if v <= 0 {
|
|
return false
|
|
}
|
|
|
|
if atomic.Casint64(ptr, v, v-1) {
|
|
return true
|
|
}
|
|
}
|
|
}
|
|
|
|
if decIfPositive(&c.dedicatedMarkWorkersNeeded) {
|
|
// This P is now dedicated to marking until the end of
|
|
// the concurrent mark phase.
|
|
_p_.gcMarkWorkerMode = gcMarkWorkerDedicatedMode
|
|
} else if c.fractionalUtilizationGoal == 0 {
|
|
// No need for fractional workers.
|
|
gcBgMarkWorkerPool.push(&node.node)
|
|
return nil
|
|
} else {
|
|
// Is this P behind on the fractional utilization
|
|
// goal?
|
|
//
|
|
// This should be kept in sync with pollFractionalWorkerExit.
|
|
delta := nanotime() - c.markStartTime
|
|
if delta > 0 && float64(_p_.gcFractionalMarkTime)/float64(delta) > c.fractionalUtilizationGoal {
|
|
// Nope. No need to run a fractional worker.
|
|
gcBgMarkWorkerPool.push(&node.node)
|
|
return nil
|
|
}
|
|
// Run a fractional worker.
|
|
_p_.gcMarkWorkerMode = gcMarkWorkerFractionalMode
|
|
}
|
|
|
|
// Run the background mark worker.
|
|
gp := node.gp.ptr()
|
|
casgstatus(gp, _Gwaiting, _Grunnable)
|
|
if trace.enabled {
|
|
traceGoUnpark(gp, 0)
|
|
}
|
|
return gp
|
|
}
|
|
|
|
// resetLive sets up the controller state for the next mark phase after the end
|
|
// of the previous one. Must be called after endCycle and before commit, before
|
|
// the world is started.
|
|
//
|
|
// The world must be stopped.
|
|
func (c *gcControllerState) resetLive(bytesMarked uint64) {
|
|
c.heapMarked = bytesMarked
|
|
c.heapLive = bytesMarked
|
|
c.heapScan = uint64(c.heapScanWork.Load())
|
|
c.lastHeapScan = uint64(c.heapScanWork.Load())
|
|
|
|
// heapLive was updated, so emit a trace event.
|
|
if trace.enabled {
|
|
traceHeapAlloc()
|
|
}
|
|
}
|
|
|
|
// logWorkTime updates mark work accounting in the controller by a duration of
|
|
// work in nanoseconds.
|
|
//
|
|
// Safe to execute at any time.
|
|
func (c *gcControllerState) logWorkTime(mode gcMarkWorkerMode, duration int64) {
|
|
switch mode {
|
|
case gcMarkWorkerDedicatedMode:
|
|
atomic.Xaddint64(&c.dedicatedMarkTime, duration)
|
|
atomic.Xaddint64(&c.dedicatedMarkWorkersNeeded, 1)
|
|
case gcMarkWorkerFractionalMode:
|
|
atomic.Xaddint64(&c.fractionalMarkTime, duration)
|
|
case gcMarkWorkerIdleMode:
|
|
atomic.Xaddint64(&c.idleMarkTime, duration)
|
|
default:
|
|
throw("logWorkTime: unknown mark worker mode")
|
|
}
|
|
}
|
|
|
|
func (c *gcControllerState) update(dHeapLive, dHeapScan int64) {
|
|
if dHeapLive != 0 {
|
|
atomic.Xadd64(&gcController.heapLive, dHeapLive)
|
|
if trace.enabled {
|
|
// gcController.heapLive changed.
|
|
traceHeapAlloc()
|
|
}
|
|
}
|
|
// Only update heapScan in the new pacer redesign if we're not
|
|
// currently in a GC.
|
|
if !goexperiment.PacerRedesign || gcBlackenEnabled == 0 {
|
|
if dHeapScan != 0 {
|
|
atomic.Xadd64(&gcController.heapScan, dHeapScan)
|
|
}
|
|
}
|
|
if gcBlackenEnabled != 0 {
|
|
// gcController.heapLive and heapScan changed.
|
|
c.revise()
|
|
}
|
|
}
|
|
|
|
func (c *gcControllerState) addScannableStack(pp *p, amount int64) {
|
|
if pp == nil {
|
|
atomic.Xadd64(&c.scannableStackSize, amount)
|
|
return
|
|
}
|
|
pp.scannableStackSizeDelta += amount
|
|
if pp.scannableStackSizeDelta >= scannableStackSizeSlack || pp.scannableStackSizeDelta <= -scannableStackSizeSlack {
|
|
atomic.Xadd64(&c.scannableStackSize, pp.scannableStackSizeDelta)
|
|
pp.scannableStackSizeDelta = 0
|
|
}
|
|
}
|
|
|
|
func (c *gcControllerState) addGlobals(amount int64) {
|
|
atomic.Xadd64(&c.globalsScan, amount)
|
|
}
|
|
|
|
// commit recomputes all pacing parameters from scratch, namely
|
|
// absolute trigger, the heap goal, mark pacing, and sweep pacing.
|
|
//
|
|
// If goexperiment.PacerRedesign is true, triggerRatio is ignored.
|
|
//
|
|
// This can be called any time. If GC is the in the middle of a
|
|
// concurrent phase, it will adjust the pacing of that phase.
|
|
//
|
|
// This depends on gcPercent, gcController.heapMarked, and
|
|
// gcController.heapLive. These must be up to date.
|
|
//
|
|
// mheap_.lock must be held or the world must be stopped.
|
|
func (c *gcControllerState) commit(triggerRatio float64) {
|
|
if !c.test {
|
|
assertWorldStoppedOrLockHeld(&mheap_.lock)
|
|
}
|
|
|
|
if !goexperiment.PacerRedesign {
|
|
c.oldCommit(triggerRatio)
|
|
return
|
|
}
|
|
|
|
// Compute the next GC goal, which is when the allocated heap
|
|
// has grown by GOGC/100 over where it started the last cycle,
|
|
// plus additional runway for non-heap sources of GC work.
|
|
goal := ^uint64(0)
|
|
if gcPercent := c.gcPercent.Load(); gcPercent >= 0 {
|
|
goal = c.heapMarked + (c.heapMarked+atomic.Load64(&c.stackScan)+atomic.Load64(&c.globalsScan))*uint64(gcPercent)/100
|
|
}
|
|
|
|
// Don't trigger below the minimum heap size.
|
|
minTrigger := c.heapMinimum
|
|
if !isSweepDone() {
|
|
// Concurrent sweep happens in the heap growth
|
|
// from gcController.heapLive to trigger, so ensure
|
|
// that concurrent sweep has some heap growth
|
|
// in which to perform sweeping before we
|
|
// start the next GC cycle.
|
|
sweepMin := atomic.Load64(&c.heapLive) + sweepMinHeapDistance
|
|
if sweepMin > minTrigger {
|
|
minTrigger = sweepMin
|
|
}
|
|
}
|
|
|
|
// If we let the trigger go too low, then if the application
|
|
// is allocating very rapidly we might end up in a situation
|
|
// where we're allocating black during a nearly always-on GC.
|
|
// The result of this is a growing heap and ultimately an
|
|
// increase in RSS. By capping us at a point >0, we're essentially
|
|
// saying that we're OK using more CPU during the GC to prevent
|
|
// this growth in RSS.
|
|
//
|
|
// The current constant was chosen empirically: given a sufficiently
|
|
// fast/scalable allocator with 48 Ps that could drive the trigger ratio
|
|
// to <0.05, this constant causes applications to retain the same peak
|
|
// RSS compared to not having this allocator.
|
|
if triggerBound := uint64(0.7*float64(goal-c.heapMarked)) + c.heapMarked; minTrigger < triggerBound {
|
|
minTrigger = triggerBound
|
|
}
|
|
|
|
// For small heaps, set the max trigger point at 95% of the heap goal.
|
|
// This ensures we always have *some* headroom when the GC actually starts.
|
|
// For larger heaps, set the max trigger point at the goal, minus the
|
|
// minimum heap size.
|
|
// This choice follows from the fact that the minimum heap size is chosen
|
|
// to reflect the costs of a GC with no work to do. With a large heap but
|
|
// very little scan work to perform, this gives us exactly as much runway
|
|
// as we would need, in the worst case.
|
|
maxRunway := uint64(0.95 * float64(goal-c.heapMarked))
|
|
if largeHeapMaxRunway := goal - c.heapMinimum; goal > c.heapMinimum && maxRunway < largeHeapMaxRunway {
|
|
maxRunway = largeHeapMaxRunway
|
|
}
|
|
maxTrigger := maxRunway + c.heapMarked
|
|
if maxTrigger < minTrigger {
|
|
maxTrigger = minTrigger
|
|
}
|
|
|
|
// Compute the trigger by using our estimate of the cons/mark ratio.
|
|
//
|
|
// The idea is to take our expected scan work, and multiply it by
|
|
// the cons/mark ratio to determine how long it'll take to complete
|
|
// that scan work in terms of bytes allocated. This gives us our GC's
|
|
// runway.
|
|
//
|
|
// However, the cons/mark ratio is a ratio of rates per CPU-second, but
|
|
// here we care about the relative rates for some division of CPU
|
|
// resources among the mutator and the GC.
|
|
//
|
|
// To summarize, we have B / cpu-ns, and we want B / ns. We get that
|
|
// by multiplying by our desired division of CPU resources. We choose
|
|
// to express CPU resources as GOMAPROCS*fraction. Note that because
|
|
// we're working with a ratio here, we can omit the number of CPU cores,
|
|
// because they'll appear in the numerator and denominator and cancel out.
|
|
// As a result, this is basically just "weighing" the cons/mark ratio by
|
|
// our desired division of resources.
|
|
//
|
|
// Furthermore, by setting the trigger so that CPU resources are divided
|
|
// this way, assuming that the cons/mark ratio is correct, we make that
|
|
// division a reality.
|
|
var trigger uint64
|
|
runway := uint64((c.consMark * (1 - gcGoalUtilization) / (gcGoalUtilization)) * float64(c.lastHeapScan+c.stackScan+c.globalsScan))
|
|
if runway > goal {
|
|
trigger = minTrigger
|
|
} else {
|
|
trigger = goal - runway
|
|
}
|
|
if trigger < minTrigger {
|
|
trigger = minTrigger
|
|
}
|
|
if trigger > maxTrigger {
|
|
trigger = maxTrigger
|
|
}
|
|
if trigger > goal {
|
|
goal = trigger
|
|
}
|
|
|
|
// Commit to the trigger and goal.
|
|
c.trigger = trigger
|
|
atomic.Store64(&c.heapGoal, goal)
|
|
if trace.enabled {
|
|
traceHeapGoal()
|
|
}
|
|
|
|
// Update mark pacing.
|
|
if gcphase != _GCoff {
|
|
c.revise()
|
|
}
|
|
}
|
|
|
|
// oldCommit sets the trigger ratio and updates everything
|
|
// derived from it: the absolute trigger, the heap goal, mark pacing,
|
|
// and sweep pacing.
|
|
//
|
|
// This can be called any time. If GC is the in the middle of a
|
|
// concurrent phase, it will adjust the pacing of that phase.
|
|
//
|
|
// This depends on gcPercent, gcController.heapMarked, and
|
|
// gcController.heapLive. These must be up to date.
|
|
//
|
|
// For !goexperiment.PacerRedesign.
|
|
func (c *gcControllerState) oldCommit(triggerRatio float64) {
|
|
gcPercent := c.gcPercent.Load()
|
|
|
|
// Compute the next GC goal, which is when the allocated heap
|
|
// has grown by GOGC/100 over the heap marked by the last
|
|
// cycle.
|
|
goal := ^uint64(0)
|
|
if gcPercent >= 0 {
|
|
goal = c.heapMarked + c.heapMarked*uint64(gcPercent)/100
|
|
}
|
|
|
|
// Set the trigger ratio, capped to reasonable bounds.
|
|
if gcPercent >= 0 {
|
|
scalingFactor := float64(gcPercent) / 100
|
|
// Ensure there's always a little margin so that the
|
|
// mutator assist ratio isn't infinity.
|
|
maxTriggerRatio := 0.95 * scalingFactor
|
|
if triggerRatio > maxTriggerRatio {
|
|
triggerRatio = maxTriggerRatio
|
|
}
|
|
|
|
// If we let triggerRatio go too low, then if the application
|
|
// is allocating very rapidly we might end up in a situation
|
|
// where we're allocating black during a nearly always-on GC.
|
|
// The result of this is a growing heap and ultimately an
|
|
// increase in RSS. By capping us at a point >0, we're essentially
|
|
// saying that we're OK using more CPU during the GC to prevent
|
|
// this growth in RSS.
|
|
//
|
|
// The current constant was chosen empirically: given a sufficiently
|
|
// fast/scalable allocator with 48 Ps that could drive the trigger ratio
|
|
// to <0.05, this constant causes applications to retain the same peak
|
|
// RSS compared to not having this allocator.
|
|
minTriggerRatio := 0.6 * scalingFactor
|
|
if triggerRatio < minTriggerRatio {
|
|
triggerRatio = minTriggerRatio
|
|
}
|
|
} else if triggerRatio < 0 {
|
|
// gcPercent < 0, so just make sure we're not getting a negative
|
|
// triggerRatio. This case isn't expected to happen in practice,
|
|
// and doesn't really matter because if gcPercent < 0 then we won't
|
|
// ever consume triggerRatio further on in this function, but let's
|
|
// just be defensive here; the triggerRatio being negative is almost
|
|
// certainly undesirable.
|
|
triggerRatio = 0
|
|
}
|
|
c.triggerRatio = triggerRatio
|
|
|
|
// Compute the absolute GC trigger from the trigger ratio.
|
|
//
|
|
// We trigger the next GC cycle when the allocated heap has
|
|
// grown by the trigger ratio over the marked heap size.
|
|
trigger := ^uint64(0)
|
|
if gcPercent >= 0 {
|
|
trigger = uint64(float64(c.heapMarked) * (1 + triggerRatio))
|
|
// Don't trigger below the minimum heap size.
|
|
minTrigger := c.heapMinimum
|
|
if !isSweepDone() {
|
|
// Concurrent sweep happens in the heap growth
|
|
// from gcController.heapLive to trigger, so ensure
|
|
// that concurrent sweep has some heap growth
|
|
// in which to perform sweeping before we
|
|
// start the next GC cycle.
|
|
sweepMin := atomic.Load64(&c.heapLive) + sweepMinHeapDistance
|
|
if sweepMin > minTrigger {
|
|
minTrigger = sweepMin
|
|
}
|
|
}
|
|
if trigger < minTrigger {
|
|
trigger = minTrigger
|
|
}
|
|
if int64(trigger) < 0 {
|
|
print("runtime: heapGoal=", c.heapGoal, " heapMarked=", c.heapMarked, " gcController.heapLive=", c.heapLive, " initialHeapLive=", work.initialHeapLive, "triggerRatio=", triggerRatio, " minTrigger=", minTrigger, "\n")
|
|
throw("trigger underflow")
|
|
}
|
|
if trigger > goal {
|
|
// The trigger ratio is always less than GOGC/100, but
|
|
// other bounds on the trigger may have raised it.
|
|
// Push up the goal, too.
|
|
goal = trigger
|
|
}
|
|
}
|
|
|
|
// Commit to the trigger and goal.
|
|
c.trigger = trigger
|
|
atomic.Store64(&c.heapGoal, goal)
|
|
if trace.enabled {
|
|
traceHeapGoal()
|
|
}
|
|
|
|
// Update mark pacing.
|
|
if gcphase != _GCoff {
|
|
c.revise()
|
|
}
|
|
}
|
|
|
|
// effectiveGrowthRatio returns the current effective heap growth
|
|
// ratio (GOGC/100) based on heapMarked from the previous GC and
|
|
// heapGoal for the current GC.
|
|
//
|
|
// This may differ from gcPercent/100 because of various upper and
|
|
// lower bounds on gcPercent. For example, if the heap is smaller than
|
|
// heapMinimum, this can be higher than gcPercent/100.
|
|
//
|
|
// mheap_.lock must be held or the world must be stopped.
|
|
func (c *gcControllerState) effectiveGrowthRatio() float64 {
|
|
if !c.test {
|
|
assertWorldStoppedOrLockHeld(&mheap_.lock)
|
|
}
|
|
|
|
egogc := float64(atomic.Load64(&c.heapGoal)-c.heapMarked) / float64(c.heapMarked)
|
|
if egogc < 0 {
|
|
// Shouldn't happen, but just in case.
|
|
egogc = 0
|
|
}
|
|
return egogc
|
|
}
|
|
|
|
// setGCPercent updates gcPercent and all related pacer state.
|
|
// Returns the old value of gcPercent.
|
|
//
|
|
// Calls gcControllerState.commit.
|
|
//
|
|
// The world must be stopped, or mheap_.lock must be held.
|
|
func (c *gcControllerState) setGCPercent(in int32) int32 {
|
|
if !c.test {
|
|
assertWorldStoppedOrLockHeld(&mheap_.lock)
|
|
}
|
|
|
|
out := c.gcPercent.Load()
|
|
if in < 0 {
|
|
in = -1
|
|
}
|
|
c.heapMinimum = defaultHeapMinimum * uint64(in) / 100
|
|
c.gcPercent.Store(in)
|
|
// Update pacing in response to gcPercent change.
|
|
c.commit(c.triggerRatio)
|
|
|
|
return out
|
|
}
|
|
|
|
//go:linkname setGCPercent runtime_1debug.setGCPercent
|
|
func setGCPercent(in int32) (out int32) {
|
|
// Run on the system stack since we grab the heap lock.
|
|
systemstack(func() {
|
|
lock(&mheap_.lock)
|
|
out = gcController.setGCPercent(in)
|
|
gcPaceSweeper(gcController.trigger)
|
|
gcPaceScavenger(gcController.heapGoal, gcController.lastHeapGoal)
|
|
unlock(&mheap_.lock)
|
|
})
|
|
|
|
// If we just disabled GC, wait for any concurrent GC mark to
|
|
// finish so we always return with no GC running.
|
|
if in < 0 {
|
|
gcWaitOnMark(atomic.Load(&work.cycles))
|
|
}
|
|
|
|
return out
|
|
}
|
|
|
|
func readGOGC() int32 {
|
|
p := gogetenv("GOGC")
|
|
if p == "off" {
|
|
return -1
|
|
}
|
|
if n, ok := atoi32(p); ok {
|
|
return n
|
|
}
|
|
return 100
|
|
}
|
|
|
|
type piController struct {
|
|
kp float64 // Proportional constant.
|
|
ti float64 // Integral time constant.
|
|
tt float64 // Reset time.
|
|
|
|
min, max float64 // Output boundaries.
|
|
|
|
// PI controller state.
|
|
|
|
errIntegral float64 // Integral of the error from t=0 to now.
|
|
|
|
// Error flags.
|
|
errOverflow bool // Set if errIntegral ever overflowed.
|
|
inputOverflow bool // Set if an operation with the input overflowed.
|
|
}
|
|
|
|
// next provides a new sample to the controller.
|
|
//
|
|
// input is the sample, setpoint is the desired point, and period is how much
|
|
// time (in whatever unit makes the most sense) has passed since the last sample.
|
|
//
|
|
// Returns a new value for the variable it's controlling, and whether the operation
|
|
// completed successfully. One reason this might fail is if error has been growing
|
|
// in an unbounded manner, to the point of overflow.
|
|
//
|
|
// In the specific case of an error overflow occurs, the errOverflow field will be
|
|
// set and the rest of the controller's internal state will be fully reset.
|
|
func (c *piController) next(input, setpoint, period float64) (float64, bool) {
|
|
// Compute the raw output value.
|
|
prop := c.kp * (setpoint - input)
|
|
rawOutput := prop + c.errIntegral
|
|
|
|
// Clamp rawOutput into output.
|
|
output := rawOutput
|
|
if isInf(output) || isNaN(output) {
|
|
// The input had a large enough magnitude that either it was already
|
|
// overflowed, or some operation with it overflowed.
|
|
// Set a flag and reset. That's the safest thing to do.
|
|
c.reset()
|
|
c.inputOverflow = true
|
|
return c.min, false
|
|
}
|
|
if output < c.min {
|
|
output = c.min
|
|
} else if output > c.max {
|
|
output = c.max
|
|
}
|
|
|
|
// Update the controller's state.
|
|
if c.ti != 0 && c.tt != 0 {
|
|
c.errIntegral += (c.kp*period/c.ti)*(setpoint-input) + (period/c.tt)*(output-rawOutput)
|
|
if isInf(c.errIntegral) || isNaN(c.errIntegral) {
|
|
// So much error has accumulated that we managed to overflow.
|
|
// The assumptions around the controller have likely broken down.
|
|
// Set a flag and reset. That's the safest thing to do.
|
|
c.reset()
|
|
c.errOverflow = true
|
|
return c.min, false
|
|
}
|
|
}
|
|
return output, true
|
|
}
|
|
|
|
// reset resets the controller state, except for controller error flags.
|
|
func (c *piController) reset() {
|
|
c.errIntegral = 0
|
|
}
|