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f1717362 | 1 | /* Copyright (C) 2005-2016 Free Software Foundation, Inc. |
1e8e9920 | 2 | Contributed by Richard Henderson <rth@redhat.com>. |
3 | ||
c35c9a62 | 4 | This file is part of the GNU Offloading and Multi Processing Library |
5 | (libgomp). | |
1e8e9920 | 6 | |
7 | Libgomp is free software; you can redistribute it and/or modify it | |
6bc9506f | 8 | under the terms of the GNU General Public License as published by |
9 | the Free Software Foundation; either version 3, or (at your option) | |
10 | any later version. | |
1e8e9920 | 11 | |
12 | Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY | |
13 | WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS | |
6bc9506f | 14 | FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
1e8e9920 | 15 | more details. |
16 | ||
6bc9506f | 17 | Under Section 7 of GPL version 3, you are granted additional |
18 | permissions described in the GCC Runtime Library Exception, version | |
19 | 3.1, as published by the Free Software Foundation. | |
20 | ||
21 | You should have received a copy of the GNU General Public License and | |
22 | a copy of the GCC Runtime Library Exception along with this program; | |
23 | see the files COPYING3 and COPYING.RUNTIME respectively. If not, see | |
24 | <http://www.gnu.org/licenses/>. */ | |
1e8e9920 | 25 | |
26 | /* This file contains routines for managing work-share iteration, both | |
27 | for loops and sections. */ | |
28 | ||
29 | #include "libgomp.h" | |
30 | #include <stdlib.h> | |
31 | ||
32 | ||
33 | /* This function implements the STATIC scheduling method. The caller should | |
34 | iterate *pstart <= x < *pend. Return zero if there are more iterations | |
35 | to perform; nonzero if not. Return less than 0 if this thread had | |
36 | received the absolutely last iteration. */ | |
37 | ||
38 | int | |
39 | gomp_iter_static_next (long *pstart, long *pend) | |
40 | { | |
41 | struct gomp_thread *thr = gomp_thread (); | |
42 | struct gomp_team *team = thr->ts.team; | |
43 | struct gomp_work_share *ws = thr->ts.work_share; | |
44 | unsigned long nthreads = team ? team->nthreads : 1; | |
45 | ||
46 | if (thr->ts.static_trip == -1) | |
47 | return -1; | |
48 | ||
49 | /* Quick test for degenerate teams and orphaned constructs. */ | |
50 | if (nthreads == 1) | |
51 | { | |
52 | *pstart = ws->next; | |
53 | *pend = ws->end; | |
54 | thr->ts.static_trip = -1; | |
55 | return ws->next == ws->end; | |
56 | } | |
57 | ||
58 | /* We interpret chunk_size zero as "unspecified", which means that we | |
59 | should break up the iterations such that each thread makes only one | |
60 | trip through the outer loop. */ | |
61 | if (ws->chunk_size == 0) | |
62 | { | |
31712e83 | 63 | unsigned long n, q, i, t; |
1e8e9920 | 64 | unsigned long s0, e0; |
65 | long s, e; | |
66 | ||
67 | if (thr->ts.static_trip > 0) | |
68 | return 1; | |
69 | ||
70 | /* Compute the total number of iterations. */ | |
71 | s = ws->incr + (ws->incr > 0 ? -1 : 1); | |
72 | n = (ws->end - ws->next + s) / ws->incr; | |
73 | i = thr->ts.team_id; | |
74 | ||
75 | /* Compute the "zero-based" start and end points. That is, as | |
76 | if the loop began at zero and incremented by one. */ | |
77 | q = n / nthreads; | |
31712e83 | 78 | t = n % nthreads; |
79 | if (i < t) | |
80 | { | |
81 | t = 0; | |
82 | q++; | |
83 | } | |
84 | s0 = q * i + t; | |
1e8e9920 | 85 | e0 = s0 + q; |
1e8e9920 | 86 | |
87 | /* Notice when no iterations allocated for this thread. */ | |
88 | if (s0 >= e0) | |
89 | { | |
90 | thr->ts.static_trip = 1; | |
91 | return 1; | |
92 | } | |
93 | ||
94 | /* Transform these to the actual start and end numbers. */ | |
95 | s = (long)s0 * ws->incr + ws->next; | |
96 | e = (long)e0 * ws->incr + ws->next; | |
97 | ||
98 | *pstart = s; | |
99 | *pend = e; | |
100 | thr->ts.static_trip = (e0 == n ? -1 : 1); | |
101 | return 0; | |
102 | } | |
103 | else | |
104 | { | |
105 | unsigned long n, s0, e0, i, c; | |
106 | long s, e; | |
107 | ||
108 | /* Otherwise, each thread gets exactly chunk_size iterations | |
109 | (if available) each time through the loop. */ | |
110 | ||
111 | s = ws->incr + (ws->incr > 0 ? -1 : 1); | |
112 | n = (ws->end - ws->next + s) / ws->incr; | |
113 | i = thr->ts.team_id; | |
114 | c = ws->chunk_size; | |
115 | ||
116 | /* Initial guess is a C sized chunk positioned nthreads iterations | |
117 | in, offset by our thread number. */ | |
118 | s0 = (thr->ts.static_trip * nthreads + i) * c; | |
119 | e0 = s0 + c; | |
120 | ||
121 | /* Detect overflow. */ | |
122 | if (s0 >= n) | |
123 | return 1; | |
124 | if (e0 > n) | |
125 | e0 = n; | |
126 | ||
127 | /* Transform these to the actual start and end numbers. */ | |
128 | s = (long)s0 * ws->incr + ws->next; | |
129 | e = (long)e0 * ws->incr + ws->next; | |
130 | ||
131 | *pstart = s; | |
132 | *pend = e; | |
133 | ||
134 | if (e0 == n) | |
135 | thr->ts.static_trip = -1; | |
136 | else | |
137 | thr->ts.static_trip++; | |
138 | return 0; | |
139 | } | |
140 | } | |
141 | ||
142 | ||
143 | /* This function implements the DYNAMIC scheduling method. Arguments are | |
144 | as for gomp_iter_static_next. This function must be called with ws->lock | |
145 | held. */ | |
146 | ||
147 | bool | |
148 | gomp_iter_dynamic_next_locked (long *pstart, long *pend) | |
149 | { | |
150 | struct gomp_thread *thr = gomp_thread (); | |
151 | struct gomp_work_share *ws = thr->ts.work_share; | |
152 | long start, end, chunk, left; | |
153 | ||
154 | start = ws->next; | |
155 | if (start == ws->end) | |
156 | return false; | |
157 | ||
fd6481cf | 158 | chunk = ws->chunk_size; |
1e8e9920 | 159 | left = ws->end - start; |
160 | if (ws->incr < 0) | |
161 | { | |
162 | if (chunk < left) | |
163 | chunk = left; | |
164 | } | |
165 | else | |
166 | { | |
167 | if (chunk > left) | |
168 | chunk = left; | |
169 | } | |
170 | end = start + chunk; | |
171 | ||
172 | ws->next = end; | |
173 | *pstart = start; | |
174 | *pend = end; | |
175 | return true; | |
176 | } | |
177 | ||
178 | ||
179 | #ifdef HAVE_SYNC_BUILTINS | |
180 | /* Similar, but doesn't require the lock held, and uses compare-and-swap | |
181 | instead. Note that the only memory value that changes is ws->next. */ | |
182 | ||
183 | bool | |
184 | gomp_iter_dynamic_next (long *pstart, long *pend) | |
185 | { | |
186 | struct gomp_thread *thr = gomp_thread (); | |
187 | struct gomp_work_share *ws = thr->ts.work_share; | |
188 | long start, end, nend, chunk, incr; | |
189 | ||
1e8e9920 | 190 | end = ws->end; |
191 | incr = ws->incr; | |
fd6481cf | 192 | chunk = ws->chunk_size; |
193 | ||
194 | if (__builtin_expect (ws->mode, 1)) | |
195 | { | |
196 | long tmp = __sync_fetch_and_add (&ws->next, chunk); | |
197 | if (incr > 0) | |
198 | { | |
199 | if (tmp >= end) | |
200 | return false; | |
201 | nend = tmp + chunk; | |
202 | if (nend > end) | |
203 | nend = end; | |
204 | *pstart = tmp; | |
205 | *pend = nend; | |
206 | return true; | |
207 | } | |
208 | else | |
209 | { | |
210 | if (tmp <= end) | |
211 | return false; | |
212 | nend = tmp + chunk; | |
213 | if (nend < end) | |
214 | nend = end; | |
215 | *pstart = tmp; | |
216 | *pend = nend; | |
217 | return true; | |
218 | } | |
219 | } | |
1e8e9920 | 220 | |
150899aa | 221 | start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED); |
1e8e9920 | 222 | while (1) |
223 | { | |
224 | long left = end - start; | |
225 | long tmp; | |
226 | ||
227 | if (start == end) | |
228 | return false; | |
229 | ||
230 | if (incr < 0) | |
231 | { | |
232 | if (chunk < left) | |
233 | chunk = left; | |
234 | } | |
235 | else | |
236 | { | |
237 | if (chunk > left) | |
238 | chunk = left; | |
239 | } | |
240 | nend = start + chunk; | |
241 | ||
242 | tmp = __sync_val_compare_and_swap (&ws->next, start, nend); | |
243 | if (__builtin_expect (tmp == start, 1)) | |
244 | break; | |
245 | ||
246 | start = tmp; | |
247 | } | |
248 | ||
249 | *pstart = start; | |
250 | *pend = nend; | |
251 | return true; | |
252 | } | |
253 | #endif /* HAVE_SYNC_BUILTINS */ | |
254 | ||
255 | ||
256 | /* This function implements the GUIDED scheduling method. Arguments are | |
257 | as for gomp_iter_static_next. This function must be called with the | |
258 | work share lock held. */ | |
259 | ||
260 | bool | |
261 | gomp_iter_guided_next_locked (long *pstart, long *pend) | |
262 | { | |
263 | struct gomp_thread *thr = gomp_thread (); | |
264 | struct gomp_work_share *ws = thr->ts.work_share; | |
265 | struct gomp_team *team = thr->ts.team; | |
266 | unsigned long nthreads = team ? team->nthreads : 1; | |
267 | unsigned long n, q; | |
268 | long start, end; | |
269 | ||
270 | if (ws->next == ws->end) | |
271 | return false; | |
272 | ||
5205ccb0 | 273 | start = ws->next; |
274 | n = (ws->end - start) / ws->incr; | |
1e8e9920 | 275 | q = (n + nthreads - 1) / nthreads; |
276 | ||
277 | if (q < ws->chunk_size) | |
278 | q = ws->chunk_size; | |
5205ccb0 | 279 | if (q <= n) |
280 | end = start + q * ws->incr; | |
281 | else | |
282 | end = ws->end; | |
1e8e9920 | 283 | |
284 | ws->next = end; | |
285 | *pstart = start; | |
286 | *pend = end; | |
287 | return true; | |
288 | } | |
289 | ||
290 | #ifdef HAVE_SYNC_BUILTINS | |
291 | /* Similar, but doesn't require the lock held, and uses compare-and-swap | |
292 | instead. Note that the only memory value that changes is ws->next. */ | |
293 | ||
294 | bool | |
295 | gomp_iter_guided_next (long *pstart, long *pend) | |
296 | { | |
297 | struct gomp_thread *thr = gomp_thread (); | |
298 | struct gomp_work_share *ws = thr->ts.work_share; | |
299 | struct gomp_team *team = thr->ts.team; | |
300 | unsigned long nthreads = team ? team->nthreads : 1; | |
301 | long start, end, nend, incr; | |
302 | unsigned long chunk_size; | |
303 | ||
150899aa | 304 | start = __atomic_load_n (&ws->next, MEMMODEL_RELAXED); |
1e8e9920 | 305 | end = ws->end; |
306 | incr = ws->incr; | |
307 | chunk_size = ws->chunk_size; | |
308 | ||
309 | while (1) | |
310 | { | |
311 | unsigned long n, q; | |
312 | long tmp; | |
313 | ||
314 | if (start == end) | |
315 | return false; | |
316 | ||
5205ccb0 | 317 | n = (end - start) / incr; |
1e8e9920 | 318 | q = (n + nthreads - 1) / nthreads; |
319 | ||
320 | if (q < chunk_size) | |
321 | q = chunk_size; | |
5205ccb0 | 322 | if (__builtin_expect (q <= n, 1)) |
323 | nend = start + q * incr; | |
324 | else | |
325 | nend = end; | |
1e8e9920 | 326 | |
327 | tmp = __sync_val_compare_and_swap (&ws->next, start, nend); | |
328 | if (__builtin_expect (tmp == start, 1)) | |
329 | break; | |
330 | ||
331 | start = tmp; | |
332 | } | |
333 | ||
334 | *pstart = start; | |
335 | *pend = nend; | |
336 | return true; | |
337 | } | |
338 | #endif /* HAVE_SYNC_BUILTINS */ |