AioContext: optimize clearing the EventNotifier
[qemu.git] / async.c
1 /*
2 * QEMU System Emulator
3 *
4 * Copyright (c) 2003-2008 Fabrice Bellard
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to deal
8 * in the Software without restriction, including without limitation the rights
9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10 * copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22 * THE SOFTWARE.
23 */
24
25 #include "qemu-common.h"
26 #include "block/aio.h"
27 #include "block/thread-pool.h"
28 #include "qemu/main-loop.h"
29 #include "qemu/atomic.h"
30
31 /***********************************************************/
32 /* bottom halves (can be seen as timers which expire ASAP) */
33
34 struct QEMUBH {
35 AioContext *ctx;
36 QEMUBHFunc *cb;
37 void *opaque;
38 QEMUBH *next;
39 bool scheduled;
40 bool idle;
41 bool deleted;
42 };
43
44 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
45 {
46 QEMUBH *bh;
47 bh = g_new(QEMUBH, 1);
48 *bh = (QEMUBH){
49 .ctx = ctx,
50 .cb = cb,
51 .opaque = opaque,
52 };
53 qemu_mutex_lock(&ctx->bh_lock);
54 bh->next = ctx->first_bh;
55 /* Make sure that the members are ready before putting bh into list */
56 smp_wmb();
57 ctx->first_bh = bh;
58 qemu_mutex_unlock(&ctx->bh_lock);
59 return bh;
60 }
61
62 /* Multiple occurrences of aio_bh_poll cannot be called concurrently */
63 int aio_bh_poll(AioContext *ctx)
64 {
65 QEMUBH *bh, **bhp, *next;
66 int ret;
67
68 ctx->walking_bh++;
69
70 ret = 0;
71 for (bh = ctx->first_bh; bh; bh = next) {
72 /* Make sure that fetching bh happens before accessing its members */
73 smp_read_barrier_depends();
74 next = bh->next;
75 /* The atomic_xchg is paired with the one in qemu_bh_schedule. The
76 * implicit memory barrier ensures that the callback sees all writes
77 * done by the scheduling thread. It also ensures that the scheduling
78 * thread sees the zero before bh->cb has run, and thus will call
79 * aio_notify again if necessary.
80 */
81 if (!bh->deleted && atomic_xchg(&bh->scheduled, 0)) {
82 if (!bh->idle)
83 ret = 1;
84 bh->idle = 0;
85 bh->cb(bh->opaque);
86 }
87 }
88
89 ctx->walking_bh--;
90
91 /* remove deleted bhs */
92 if (!ctx->walking_bh) {
93 qemu_mutex_lock(&ctx->bh_lock);
94 bhp = &ctx->first_bh;
95 while (*bhp) {
96 bh = *bhp;
97 if (bh->deleted) {
98 *bhp = bh->next;
99 g_free(bh);
100 } else {
101 bhp = &bh->next;
102 }
103 }
104 qemu_mutex_unlock(&ctx->bh_lock);
105 }
106
107 return ret;
108 }
109
110 void qemu_bh_schedule_idle(QEMUBH *bh)
111 {
112 bh->idle = 1;
113 /* Make sure that idle & any writes needed by the callback are done
114 * before the locations are read in the aio_bh_poll.
115 */
116 atomic_mb_set(&bh->scheduled, 1);
117 }
118
119 void qemu_bh_schedule(QEMUBH *bh)
120 {
121 AioContext *ctx;
122
123 ctx = bh->ctx;
124 bh->idle = 0;
125 /* The memory barrier implicit in atomic_xchg makes sure that:
126 * 1. idle & any writes needed by the callback are done before the
127 * locations are read in the aio_bh_poll.
128 * 2. ctx is loaded before scheduled is set and the callback has a chance
129 * to execute.
130 */
131 if (atomic_xchg(&bh->scheduled, 1) == 0) {
132 aio_notify(ctx);
133 }
134 }
135
136
137 /* This func is async.
138 */
139 void qemu_bh_cancel(QEMUBH *bh)
140 {
141 bh->scheduled = 0;
142 }
143
144 /* This func is async.The bottom half will do the delete action at the finial
145 * end.
146 */
147 void qemu_bh_delete(QEMUBH *bh)
148 {
149 bh->scheduled = 0;
150 bh->deleted = 1;
151 }
152
153 int64_t
154 aio_compute_timeout(AioContext *ctx)
155 {
156 int64_t deadline;
157 int timeout = -1;
158 QEMUBH *bh;
159
160 for (bh = ctx->first_bh; bh; bh = bh->next) {
161 if (!bh->deleted && bh->scheduled) {
162 if (bh->idle) {
163 /* idle bottom halves will be polled at least
164 * every 10ms */
165 timeout = 10000000;
166 } else {
167 /* non-idle bottom halves will be executed
168 * immediately */
169 return 0;
170 }
171 }
172 }
173
174 deadline = timerlistgroup_deadline_ns(&ctx->tlg);
175 if (deadline == 0) {
176 return 0;
177 } else {
178 return qemu_soonest_timeout(timeout, deadline);
179 }
180 }
181
182 static gboolean
183 aio_ctx_prepare(GSource *source, gint *timeout)
184 {
185 AioContext *ctx = (AioContext *) source;
186
187 atomic_or(&ctx->notify_me, 1);
188
189 /* We assume there is no timeout already supplied */
190 *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
191
192 if (aio_prepare(ctx)) {
193 *timeout = 0;
194 }
195
196 return *timeout == 0;
197 }
198
199 static gboolean
200 aio_ctx_check(GSource *source)
201 {
202 AioContext *ctx = (AioContext *) source;
203 QEMUBH *bh;
204
205 atomic_and(&ctx->notify_me, ~1);
206 aio_notify_accept(ctx);
207
208 for (bh = ctx->first_bh; bh; bh = bh->next) {
209 if (!bh->deleted && bh->scheduled) {
210 return true;
211 }
212 }
213 return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
214 }
215
216 static gboolean
217 aio_ctx_dispatch(GSource *source,
218 GSourceFunc callback,
219 gpointer user_data)
220 {
221 AioContext *ctx = (AioContext *) source;
222
223 assert(callback == NULL);
224 aio_dispatch(ctx);
225 return true;
226 }
227
228 static void
229 aio_ctx_finalize(GSource *source)
230 {
231 AioContext *ctx = (AioContext *) source;
232
233 thread_pool_free(ctx->thread_pool);
234 aio_set_event_notifier(ctx, &ctx->notifier, NULL);
235 event_notifier_cleanup(&ctx->notifier);
236 rfifolock_destroy(&ctx->lock);
237 qemu_mutex_destroy(&ctx->bh_lock);
238 timerlistgroup_deinit(&ctx->tlg);
239 }
240
241 static GSourceFuncs aio_source_funcs = {
242 aio_ctx_prepare,
243 aio_ctx_check,
244 aio_ctx_dispatch,
245 aio_ctx_finalize
246 };
247
248 GSource *aio_get_g_source(AioContext *ctx)
249 {
250 g_source_ref(&ctx->source);
251 return &ctx->source;
252 }
253
254 ThreadPool *aio_get_thread_pool(AioContext *ctx)
255 {
256 if (!ctx->thread_pool) {
257 ctx->thread_pool = thread_pool_new(ctx);
258 }
259 return ctx->thread_pool;
260 }
261
262 void aio_notify(AioContext *ctx)
263 {
264 /* Write e.g. bh->scheduled before reading ctx->notify_me. Pairs
265 * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
266 */
267 smp_mb();
268 if (ctx->notify_me) {
269 event_notifier_set(&ctx->notifier);
270 atomic_mb_set(&ctx->notified, true);
271 }
272 }
273
274 void aio_notify_accept(AioContext *ctx)
275 {
276 if (atomic_xchg(&ctx->notified, false)) {
277 event_notifier_test_and_clear(&ctx->notifier);
278 }
279 }
280
281 static void aio_timerlist_notify(void *opaque)
282 {
283 aio_notify(opaque);
284 }
285
286 static void aio_rfifolock_cb(void *opaque)
287 {
288 /* Kick owner thread in case they are blocked in aio_poll() */
289 aio_notify(opaque);
290 }
291
292 static void event_notifier_dummy_cb(EventNotifier *e)
293 {
294 }
295
296 AioContext *aio_context_new(Error **errp)
297 {
298 int ret;
299 AioContext *ctx;
300 ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
301 ret = event_notifier_init(&ctx->notifier, false);
302 if (ret < 0) {
303 g_source_destroy(&ctx->source);
304 error_setg_errno(errp, -ret, "Failed to initialize event notifier");
305 return NULL;
306 }
307 g_source_set_can_recurse(&ctx->source, true);
308 aio_set_event_notifier(ctx, &ctx->notifier,
309 (EventNotifierHandler *)
310 event_notifier_dummy_cb);
311 ctx->thread_pool = NULL;
312 qemu_mutex_init(&ctx->bh_lock);
313 rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
314 timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
315
316 return ctx;
317 }
318
319 void aio_context_ref(AioContext *ctx)
320 {
321 g_source_ref(&ctx->source);
322 }
323
324 void aio_context_unref(AioContext *ctx)
325 {
326 g_source_unref(&ctx->source);
327 }
328
329 void aio_context_acquire(AioContext *ctx)
330 {
331 rfifolock_lock(&ctx->lock);
332 }
333
334 void aio_context_release(AioContext *ctx)
335 {
336 rfifolock_unlock(&ctx->lock);
337 }