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/* Copyright (C) 2005, 2008, 2009 Free Software Foundation, Inc. Contributed by Richard Henderson <rth@redhat.com>. This file is part of the GNU OpenMP Library (libgomp). Libgomp is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. Under Section 7 of GPL version 3, you are granted additional permissions described in the GCC Runtime Library Exception, version 3.1, as published by the Free Software Foundation. You should have received a copy of the GNU General Public License and a copy of the GCC Runtime Library Exception along with this program; see the files COPYING3 and COPYING.RUNTIME respectively. If not, see <http://www.gnu.org/licenses/>. */ /* This file contains routines for managing work-share iteration, both for loops and sections. */ #include "libgomp.h" #include <stdlib.h> /* This function implements the STATIC scheduling method. The caller should iterate *pstart <= x < *pend. Return zero if there are more iterations to perform; nonzero if not. Return less than 0 if this thread had received the absolutely last iteration. */ int gomp_iter_static_next (long *pstart, long *pend) { struct gomp_thread *thr = gomp_thread (); struct gomp_team *team = thr->ts.team; struct gomp_work_share *ws = thr->ts.work_share; unsigned long nthreads = team ? team->nthreads : 1; if (thr->ts.static_trip == -1) return -1; /* Quick test for degenerate teams and orphaned constructs. */ if (nthreads == 1) { *pstart = ws->next; *pend = ws->end; thr->ts.static_trip = -1; return ws->next == ws->end; } /* We interpret chunk_size zero as "unspecified", which means that we should break up the iterations such that each thread makes only one trip through the outer loop. */ if (ws->chunk_size == 0) { unsigned long n, q, i; unsigned long s0, e0; long s, e; if (thr->ts.static_trip > 0) return 1; /* Compute the total number of iterations. */ s = ws->incr + (ws->incr > 0 ? -1 : 1); n = (ws->end - ws->next + s) / ws->incr; i = thr->ts.team_id; /* Compute the "zero-based" start and end points. That is, as if the loop began at zero and incremented by one. */ q = n / nthreads; q += (q * nthreads != n); s0 = q * i; e0 = s0 + q; if (e0 > n) e0 = n; /* Notice when no iterations allocated for this thread. */ if (s0 >= e0) { thr->ts.static_trip = 1; return 1; } /* Transform these to the actual start and end numbers. */ s = (long)s0 * ws->incr + ws->next; e = (long)e0 * ws->incr + ws->next; *pstart = s; *pend = e; thr->ts.static_trip = (e0 == n ? -1 : 1); return 0; } else { unsigned long n, s0, e0, i, c; long s, e; /* Otherwise, each thread gets exactly chunk_size iterations (if available) each time through the loop. */ s = ws->incr + (ws->incr > 0 ? -1 : 1); n = (ws->end - ws->next + s) / ws->incr; i = thr->ts.team_id; c = ws->chunk_size; /* Initial guess is a C sized chunk positioned nthreads iterations in, offset by our thread number. */ s0 = (thr->ts.static_trip * nthreads + i) * c; e0 = s0 + c; /* Detect overflow. */ if (s0 >= n) return 1; if (e0 > n) e0 = n; /* Transform these to the actual start and end numbers. */ s = (long)s0 * ws->incr + ws->next; e = (long)e0 * ws->incr + ws->next; *pstart = s; *pend = e; if (e0 == n) thr->ts.static_trip = -1; else thr->ts.static_trip++; return 0; } } /* This function implements the DYNAMIC scheduling method. Arguments are as for gomp_iter_static_next. This function must be called with ws->lock held. */ bool gomp_iter_dynamic_next_locked (long *pstart, long *pend) { struct gomp_thread *thr = gomp_thread (); struct gomp_work_share *ws = thr->ts.work_share; long start, end, chunk, left; start = ws->next; if (start == ws->end) return false; chunk = ws->chunk_size; left = ws->end - start; if (ws->incr < 0) { if (chunk < left) chunk = left; } else { if (chunk > left) chunk = left; } end = start + chunk; ws->next = end; *pstart = start; *pend = end; return true; } #ifdef HAVE_SYNC_BUILTINS /* Similar, but doesn't require the lock held, and uses compare-and-swap instead. Note that the only memory value that changes is ws->next. */ bool gomp_iter_dynamic_next (long *pstart, long *pend) { struct gomp_thread *thr = gomp_thread (); struct gomp_work_share *ws = thr->ts.work_share; long start, end, nend, chunk, incr; end = ws->end; incr = ws->incr; chunk = ws->chunk_size; if (__builtin_expect (ws->mode, 1)) { long tmp = __sync_fetch_and_add (&ws->next, chunk); if (incr > 0) { if (tmp >= end) return false; nend = tmp + chunk; if (nend > end) nend = end; *pstart = tmp; *pend = nend; return true; } else { if (tmp <= end) return false; nend = tmp + chunk; if (nend < end) nend = end; *pstart = tmp; *pend = nend; return true; } } start = ws->next; while (1) { long left = end - start; long tmp; if (start == end) return false; if (incr < 0) { if (chunk < left) chunk = left; } else { if (chunk > left) chunk = left; } nend = start + chunk; tmp = __sync_val_compare_and_swap (&ws->next, start, nend); if (__builtin_expect (tmp == start, 1)) break; start = tmp; } *pstart = start; *pend = nend; return true; } #endif /* HAVE_SYNC_BUILTINS */ /* This function implements the GUIDED scheduling method. Arguments are as for gomp_iter_static_next. This function must be called with the work share lock held. */ bool gomp_iter_guided_next_locked (long *pstart, long *pend) { struct gomp_thread *thr = gomp_thread (); struct gomp_work_share *ws = thr->ts.work_share; struct gomp_team *team = thr->ts.team; unsigned long nthreads = team ? team->nthreads : 1; unsigned long n, q; long start, end; if (ws->next == ws->end) return false; start = ws->next; n = (ws->end - start) / ws->incr; q = (n + nthreads - 1) / nthreads; if (q < ws->chunk_size) q = ws->chunk_size; if (q <= n) end = start + q * ws->incr; else end = ws->end; ws->next = end; *pstart = start; *pend = end; return true; } #ifdef HAVE_SYNC_BUILTINS /* Similar, but doesn't require the lock held, and uses compare-and-swap instead. Note that the only memory value that changes is ws->next. */ bool gomp_iter_guided_next (long *pstart, long *pend) { struct gomp_thread *thr = gomp_thread (); struct gomp_work_share *ws = thr->ts.work_share; struct gomp_team *team = thr->ts.team; unsigned long nthreads = team ? team->nthreads : 1; long start, end, nend, incr; unsigned long chunk_size; start = ws->next; end = ws->end; incr = ws->incr; chunk_size = ws->chunk_size; while (1) { unsigned long n, q; long tmp; if (start == end) return false; n = (end - start) / incr; q = (n + nthreads - 1) / nthreads; if (q < chunk_size) q = chunk_size; if (__builtin_expect (q <= n, 1)) nend = start + q * incr; else nend = end; tmp = __sync_val_compare_and_swap (&ws->next, start, nend); if (__builtin_expect (tmp == start, 1)) break; start = tmp; } *pstart = start; *pend = nend; return true; } #endif /* HAVE_SYNC_BUILTINS */
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