/* Copyright (C) 2005-2021 Free Software Foundation, Inc. | |

Contributed by Richard Henderson <rth@redhat.com>. | |

This file is part of the GNU Offloading and Multi Processing 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, t; | |

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; | |

t = n % nthreads; | |

if (i < t) | |

{ | |

t = 0; | |

q++; | |

} | |

s0 = q * i + t; | |

e0 = s0 + q; | |

/* 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 = __atomic_load_n (&ws->next, MEMMODEL_RELAXED); | |

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 = __atomic_load_n (&ws->next, MEMMODEL_RELAXED); | |

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 */ |