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1 /*
2 * Event loop thread
3 *
4 * Copyright Red Hat Inc., 2013, 2020
5 *
6 * Authors:
7 * Stefan Hajnoczi <stefanha@redhat.com>
8 *
9 * This work is licensed under the terms of the GNU GPL, version 2 or later.
10 * See the COPYING file in the top-level directory.
11 *
12 */
13
14 #include "qemu/osdep.h"
15 #include "qom/object.h"
16 #include "qom/object_interfaces.h"
17 #include "qemu/module.h"
18 #include "block/aio.h"
19 #include "block/block.h"
20 #include "sysemu/event-loop-base.h"
21 #include "sysemu/iothread.h"
22 #include "qapi/error.h"
23 #include "qapi/qapi-commands-misc.h"
24 #include "qemu/error-report.h"
25 #include "qemu/rcu.h"
26 #include "qemu/main-loop.h"
27
28
29 #ifdef CONFIG_POSIX
30 /* Benchmark results from 2016 on NVMe SSD drives show max polling times around
31 * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32
32 * workloads.
33 */
34 #define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL
35 #else
36 #define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL
37 #endif
38
39 static void *iothread_run(void *opaque)
40 {
41 IOThread *iothread = opaque;
42
43 rcu_register_thread();
44 /*
45 * g_main_context_push_thread_default() must be called before anything
46 * in this new thread uses glib.
47 */
48 g_main_context_push_thread_default(iothread->worker_context);
49 qemu_set_current_aio_context(iothread->ctx);
50 iothread->thread_id = qemu_get_thread_id();
51 qemu_sem_post(&iothread->init_done_sem);
52
53 while (iothread->running) {
54 /*
55 * Note: from functional-wise the g_main_loop_run() below can
56 * already cover the aio_poll() events, but we can't run the
57 * main loop unconditionally because explicit aio_poll() here
58 * is faster than g_main_loop_run() when we do not need the
59 * gcontext at all (e.g., pure block layer iothreads). In
60 * other words, when we want to run the gcontext with the
61 * iothread we need to pay some performance for functionality.
62 */
63 aio_poll(iothread->ctx, true);
64
65 /*
66 * We must check the running state again in case it was
67 * changed in previous aio_poll()
68 */
69 if (iothread->running && qatomic_read(&iothread->run_gcontext)) {
70 g_main_loop_run(iothread->main_loop);
71 }
72 }
73
74 g_main_context_pop_thread_default(iothread->worker_context);
75 rcu_unregister_thread();
76 return NULL;
77 }
78
79 /* Runs in iothread_run() thread */
80 static void iothread_stop_bh(void *opaque)
81 {
82 IOThread *iothread = opaque;
83
84 iothread->running = false; /* stop iothread_run() */
85
86 if (iothread->main_loop) {
87 g_main_loop_quit(iothread->main_loop);
88 }
89 }
90
91 void iothread_stop(IOThread *iothread)
92 {
93 if (!iothread->ctx || iothread->stopping) {
94 return;
95 }
96 iothread->stopping = true;
97 aio_bh_schedule_oneshot(iothread->ctx, iothread_stop_bh, iothread);
98 qemu_thread_join(&iothread->thread);
99 }
100
101 static void iothread_instance_init(Object *obj)
102 {
103 IOThread *iothread = IOTHREAD(obj);
104
105 iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;
106 iothread->thread_id = -1;
107 qemu_sem_init(&iothread->init_done_sem, 0);
108 /* By default, we don't run gcontext */
109 qatomic_set(&iothread->run_gcontext, 0);
110 }
111
112 static void iothread_instance_finalize(Object *obj)
113 {
114 IOThread *iothread = IOTHREAD(obj);
115
116 iothread_stop(iothread);
117
118 /*
119 * Before glib2 2.33.10, there is a glib2 bug that GSource context
120 * pointer may not be cleared even if the context has already been
121 * destroyed (while it should). Here let's free the AIO context
122 * earlier to bypass that glib bug.
123 *
124 * We can remove this comment after the minimum supported glib2
125 * version boosts to 2.33.10. Before that, let's free the
126 * GSources first before destroying any GMainContext.
127 */
128 if (iothread->ctx) {
129 aio_context_unref(iothread->ctx);
130 iothread->ctx = NULL;
131 }
132 if (iothread->worker_context) {
133 g_main_context_unref(iothread->worker_context);
134 iothread->worker_context = NULL;
135 g_main_loop_unref(iothread->main_loop);
136 iothread->main_loop = NULL;
137 }
138 qemu_sem_destroy(&iothread->init_done_sem);
139 }
140
141 static void iothread_init_gcontext(IOThread *iothread)
142 {
143 GSource *source;
144
145 iothread->worker_context = g_main_context_new();
146 source = aio_get_g_source(iothread_get_aio_context(iothread));
147 g_source_attach(source, iothread->worker_context);
148 g_source_unref(source);
149 iothread->main_loop = g_main_loop_new(iothread->worker_context, TRUE);
150 }
151
152 static void iothread_set_aio_context_params(EventLoopBase *base, Error **errp)
153 {
154 ERRP_GUARD();
155 IOThread *iothread = IOTHREAD(base);
156
157 if (!iothread->ctx) {
158 return;
159 }
160
161 aio_context_set_poll_params(iothread->ctx,
162 iothread->poll_max_ns,
163 iothread->poll_grow,
164 iothread->poll_shrink,
165 errp);
166 if (*errp) {
167 return;
168 }
169
170 aio_context_set_aio_params(iothread->ctx,
171 iothread->parent_obj.aio_max_batch,
172 errp);
173
174 aio_context_set_thread_pool_params(iothread->ctx, base->thread_pool_min,
175 base->thread_pool_max, errp);
176 }
177
178
179 static void iothread_init(EventLoopBase *base, Error **errp)
180 {
181 Error *local_error = NULL;
182 IOThread *iothread = IOTHREAD(base);
183 char *thread_name;
184
185 iothread->stopping = false;
186 iothread->running = true;
187 iothread->ctx = aio_context_new(errp);
188 if (!iothread->ctx) {
189 return;
190 }
191
192 /*
193 * Init one GMainContext for the iothread unconditionally, even if
194 * it's not used
195 */
196 iothread_init_gcontext(iothread);
197
198 iothread_set_aio_context_params(base, &local_error);
199 if (local_error) {
200 error_propagate(errp, local_error);
201 aio_context_unref(iothread->ctx);
202 iothread->ctx = NULL;
203 return;
204 }
205
206 /* This assumes we are called from a thread with useful CPU affinity for us
207 * to inherit.
208 */
209 thread_name = g_strdup_printf("IO %s",
210 object_get_canonical_path_component(OBJECT(base)));
211 qemu_thread_create(&iothread->thread, thread_name, iothread_run,
212 iothread, QEMU_THREAD_JOINABLE);
213 g_free(thread_name);
214
215 /* Wait for initialization to complete */
216 while (iothread->thread_id == -1) {
217 qemu_sem_wait(&iothread->init_done_sem);
218 }
219 }
220
221 typedef struct {
222 const char *name;
223 ptrdiff_t offset; /* field's byte offset in IOThread struct */
224 } IOThreadParamInfo;
225
226 static IOThreadParamInfo poll_max_ns_info = {
227 "poll-max-ns", offsetof(IOThread, poll_max_ns),
228 };
229 static IOThreadParamInfo poll_grow_info = {
230 "poll-grow", offsetof(IOThread, poll_grow),
231 };
232 static IOThreadParamInfo poll_shrink_info = {
233 "poll-shrink", offsetof(IOThread, poll_shrink),
234 };
235
236 static void iothread_get_param(Object *obj, Visitor *v,
237 const char *name, IOThreadParamInfo *info, Error **errp)
238 {
239 IOThread *iothread = IOTHREAD(obj);
240 int64_t *field = (void *)iothread + info->offset;
241
242 visit_type_int64(v, name, field, errp);
243 }
244
245 static bool iothread_set_param(Object *obj, Visitor *v,
246 const char *name, IOThreadParamInfo *info, Error **errp)
247 {
248 IOThread *iothread = IOTHREAD(obj);
249 int64_t *field = (void *)iothread + info->offset;
250 int64_t value;
251
252 if (!visit_type_int64(v, name, &value, errp)) {
253 return false;
254 }
255
256 if (value < 0) {
257 error_setg(errp, "%s value must be in range [0, %" PRId64 "]",
258 info->name, INT64_MAX);
259 return false;
260 }
261
262 *field = value;
263
264 return true;
265 }
266
267 static void iothread_get_poll_param(Object *obj, Visitor *v,
268 const char *name, void *opaque, Error **errp)
269 {
270 IOThreadParamInfo *info = opaque;
271
272 iothread_get_param(obj, v, name, info, errp);
273 }
274
275 static void iothread_set_poll_param(Object *obj, Visitor *v,
276 const char *name, void *opaque, Error **errp)
277 {
278 IOThread *iothread = IOTHREAD(obj);
279 IOThreadParamInfo *info = opaque;
280
281 if (!iothread_set_param(obj, v, name, info, errp)) {
282 return;
283 }
284
285 if (iothread->ctx) {
286 aio_context_set_poll_params(iothread->ctx,
287 iothread->poll_max_ns,
288 iothread->poll_grow,
289 iothread->poll_shrink,
290 errp);
291 }
292 }
293
294 static void iothread_class_init(ObjectClass *klass, void *class_data)
295 {
296 EventLoopBaseClass *bc = EVENT_LOOP_BASE_CLASS(klass);
297
298 bc->init = iothread_init;
299 bc->update_params = iothread_set_aio_context_params;
300
301 object_class_property_add(klass, "poll-max-ns", "int",
302 iothread_get_poll_param,
303 iothread_set_poll_param,
304 NULL, &poll_max_ns_info);
305 object_class_property_add(klass, "poll-grow", "int",
306 iothread_get_poll_param,
307 iothread_set_poll_param,
308 NULL, &poll_grow_info);
309 object_class_property_add(klass, "poll-shrink", "int",
310 iothread_get_poll_param,
311 iothread_set_poll_param,
312 NULL, &poll_shrink_info);
313 }
314
315 static const TypeInfo iothread_info = {
316 .name = TYPE_IOTHREAD,
317 .parent = TYPE_EVENT_LOOP_BASE,
318 .class_init = iothread_class_init,
319 .instance_size = sizeof(IOThread),
320 .instance_init = iothread_instance_init,
321 .instance_finalize = iothread_instance_finalize,
322 };
323
324 static void iothread_register_types(void)
325 {
326 type_register_static(&iothread_info);
327 }
328
329 type_init(iothread_register_types)
330
331 char *iothread_get_id(IOThread *iothread)
332 {
333 return g_strdup(object_get_canonical_path_component(OBJECT(iothread)));
334 }
335
336 AioContext *iothread_get_aio_context(IOThread *iothread)
337 {
338 return iothread->ctx;
339 }
340
341 static int query_one_iothread(Object *object, void *opaque)
342 {
343 IOThreadInfoList ***tail = opaque;
344 IOThreadInfo *info;
345 IOThread *iothread;
346
347 iothread = (IOThread *)object_dynamic_cast(object, TYPE_IOTHREAD);
348 if (!iothread) {
349 return 0;
350 }
351
352 info = g_new0(IOThreadInfo, 1);
353 info->id = iothread_get_id(iothread);
354 info->thread_id = iothread->thread_id;
355 info->poll_max_ns = iothread->poll_max_ns;
356 info->poll_grow = iothread->poll_grow;
357 info->poll_shrink = iothread->poll_shrink;
358 info->aio_max_batch = iothread->parent_obj.aio_max_batch;
359
360 QAPI_LIST_APPEND(*tail, info);
361 return 0;
362 }
363
364 IOThreadInfoList *qmp_query_iothreads(Error **errp)
365 {
366 IOThreadInfoList *head = NULL;
367 IOThreadInfoList **prev = &head;
368 Object *container = object_get_objects_root();
369
370 object_child_foreach(container, query_one_iothread, &prev);
371 return head;
372 }
373
374 GMainContext *iothread_get_g_main_context(IOThread *iothread)
375 {
376 qatomic_set(&iothread->run_gcontext, 1);
377 aio_notify(iothread->ctx);
378 return iothread->worker_context;
379 }
380
381 IOThread *iothread_create(const char *id, Error **errp)
382 {
383 Object *obj;
384
385 obj = object_new_with_props(TYPE_IOTHREAD,
386 object_get_internal_root(),
387 id, errp, NULL);
388
389 return IOTHREAD(obj);
390 }
391
392 void iothread_destroy(IOThread *iothread)
393 {
394 object_unparent(OBJECT(iothread));
395 }
396
397 /* Lookup IOThread by its id. Only finds user-created objects, not internal
398 * iothread_create() objects. */
399 IOThread *iothread_by_id(const char *id)
400 {
401 return IOTHREAD(object_resolve_path_type(id, TYPE_IOTHREAD, NULL));
402 }
403
404 bool qemu_in_iothread(void)
405 {
406 return qemu_get_current_aio_context() == qemu_get_aio_context() ?
407 false : true;
408 }