339 lines
8 KiB
C
339 lines
8 KiB
C
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/* Copyright (C) 2005-2022 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Offloading and Multi Processing Library
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(libgomp).
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Libgomp is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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/* This file contains routines for managing work-share iteration, both
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for loops and sections. */
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#include "libgomp.h"
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#include <stdlib.h>
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/* This function implements the STATIC scheduling method. The caller should
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iterate *pstart <= x < *pend. Return zero if there are more iterations
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to perform; nonzero if not. Return less than 0 if this thread had
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received the absolutely last iteration. */
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int
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gomp_iter_static_next (long *pstart, long *pend)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_team *team = thr->ts.team;
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struct gomp_work_share *ws = thr->ts.work_share;
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unsigned long nthreads = team ? team->nthreads : 1;
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if (thr->ts.static_trip == -1)
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return -1;
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/* Quick test for degenerate teams and orphaned constructs. */
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if (nthreads == 1)
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{
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*pstart = ws->next;
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*pend = ws->end;
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thr->ts.static_trip = -1;
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return ws->next == ws->end;
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}
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/* We interpret chunk_size zero as "unspecified", which means that we
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should break up the iterations such that each thread makes only one
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trip through the outer loop. */
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if (ws->chunk_size == 0)
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{
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unsigned long n, q, i, t;
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unsigned long s0, e0;
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long s, e;
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if (thr->ts.static_trip > 0)
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return 1;
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/* Compute the total number of iterations. */
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s = ws->incr + (ws->incr > 0 ? -1 : 1);
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n = (ws->end - ws->next + s) / ws->incr;
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i = thr->ts.team_id;
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/* Compute the "zero-based" start and end points. That is, as
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if the loop began at zero and incremented by one. */
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q = n / nthreads;
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t = n % nthreads;
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if (i < t)
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{
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t = 0;
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q++;
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}
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s0 = q * i + t;
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e0 = s0 + q;
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/* Notice when no iterations allocated for this thread. */
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if (s0 >= e0)
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{
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thr->ts.static_trip = 1;
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return 1;
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}
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/* Transform these to the actual start and end numbers. */
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s = (long)s0 * ws->incr + ws->next;
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e = (long)e0 * ws->incr + ws->next;
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*pstart = s;
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*pend = e;
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thr->ts.static_trip = (e0 == n ? -1 : 1);
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return 0;
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}
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else
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{
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unsigned long n, s0, e0, i, c;
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long s, e;
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/* Otherwise, each thread gets exactly chunk_size iterations
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(if available) each time through the loop. */
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s = ws->incr + (ws->incr > 0 ? -1 : 1);
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n = (ws->end - ws->next + s) / ws->incr;
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i = thr->ts.team_id;
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c = ws->chunk_size;
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/* Initial guess is a C sized chunk positioned nthreads iterations
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in, offset by our thread number. */
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s0 = (thr->ts.static_trip * nthreads + i) * c;
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e0 = s0 + c;
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/* Detect overflow. */
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if (s0 >= n)
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return 1;
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if (e0 > n)
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e0 = n;
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/* Transform these to the actual start and end numbers. */
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s = (long)s0 * ws->incr + ws->next;
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e = (long)e0 * ws->incr + ws->next;
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*pstart = s;
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*pend = e;
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if (e0 == n)
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thr->ts.static_trip = -1;
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else
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thr->ts.static_trip++;
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return 0;
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}
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}
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/* This function implements the DYNAMIC scheduling method. Arguments are
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as for gomp_iter_static_next. This function must be called with ws->lock
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held. */
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bool
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gomp_iter_dynamic_next_locked (long *pstart, long *pend)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_work_share *ws = thr->ts.work_share;
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long start, end, chunk, left;
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start = ws->next;
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if (start == ws->end)
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return false;
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chunk = ws->chunk_size;
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left = ws->end - start;
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if (ws->incr < 0)
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{
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if (chunk < left)
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chunk = left;
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}
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else
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{
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if (chunk > left)
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chunk = left;
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}
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end = start + chunk;
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ws->next = end;
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*pstart = start;
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*pend = end;
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return true;
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}
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#ifdef HAVE_SYNC_BUILTINS
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/* Similar, but doesn't require the lock held, and uses compare-and-swap
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instead. Note that the only memory value that changes is ws->next. */
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bool
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gomp_iter_dynamic_next (long *pstart, long *pend)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_work_share *ws = thr->ts.work_share;
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long start, end, nend, chunk, incr;
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end = ws->end;
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incr = ws->incr;
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chunk = ws->chunk_size;
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if (__builtin_expect (ws->mode, 1))
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{
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long tmp = __sync_fetch_and_add (&ws->next, chunk);
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if (incr > 0)
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{
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if (tmp >= end)
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return false;
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nend = tmp + chunk;
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if (nend > end)
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nend = end;
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*pstart = tmp;
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*pend = nend;
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return true;
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}
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else
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{
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if (tmp <= end)
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return false;
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nend = tmp + chunk;
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if (nend < end)
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nend = end;
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*pstart = tmp;
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*pend = nend;
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return true;
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}
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}
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start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED);
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while (1)
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{
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long left = end - start;
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long tmp;
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if (start == end)
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return false;
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if (incr < 0)
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{
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if (chunk < left)
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chunk = left;
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}
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else
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{
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if (chunk > left)
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chunk = left;
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}
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nend = start + chunk;
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tmp = __sync_val_compare_and_swap (&ws->next, start, nend);
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if (__builtin_expect (tmp == start, 1))
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break;
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start = tmp;
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}
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*pstart = start;
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*pend = nend;
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return true;
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}
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#endif /* HAVE_SYNC_BUILTINS */
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/* This function implements the GUIDED scheduling method. Arguments are
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as for gomp_iter_static_next. This function must be called with the
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work share lock held. */
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bool
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gomp_iter_guided_next_locked (long *pstart, long *pend)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_work_share *ws = thr->ts.work_share;
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struct gomp_team *team = thr->ts.team;
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unsigned long nthreads = team ? team->nthreads : 1;
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unsigned long n, q;
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long start, end;
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if (ws->next == ws->end)
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return false;
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start = ws->next;
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n = (ws->end - start) / ws->incr;
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q = (n + nthreads - 1) / nthreads;
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if (q < ws->chunk_size)
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q = ws->chunk_size;
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if (q <= n)
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end = start + q * ws->incr;
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else
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end = ws->end;
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ws->next = end;
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*pstart = start;
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*pend = end;
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return true;
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}
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#ifdef HAVE_SYNC_BUILTINS
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/* Similar, but doesn't require the lock held, and uses compare-and-swap
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instead. Note that the only memory value that changes is ws->next. */
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bool
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gomp_iter_guided_next (long *pstart, long *pend)
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{
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struct gomp_thread *thr = gomp_thread ();
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struct gomp_work_share *ws = thr->ts.work_share;
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struct gomp_team *team = thr->ts.team;
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unsigned long nthreads = team ? team->nthreads : 1;
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long start, end, nend, incr;
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unsigned long chunk_size;
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start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED);
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end = ws->end;
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incr = ws->incr;
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chunk_size = ws->chunk_size;
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while (1)
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{
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unsigned long n, q;
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long tmp;
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if (start == end)
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return false;
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n = (end - start) / incr;
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q = (n + nthreads - 1) / nthreads;
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if (q < chunk_size)
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q = chunk_size;
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if (__builtin_expect (q <= n, 1))
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nend = start + q * incr;
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else
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nend = end;
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tmp = __sync_val_compare_and_swap (&ws->next, start, nend);
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if (__builtin_expect (tmp == start, 1))
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break;
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start = tmp;
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}
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*pstart = start;
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*pend = nend;
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return true;
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}
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#endif /* HAVE_SYNC_BUILTINS */
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