*/
#include "qemu-common.h"
-#include "qemu-aio.h"
-
-/*
- * An AsyncContext protects the callbacks of AIO requests and Bottom Halves
- * against interfering with each other. A typical example is qcow2 that accepts
- * asynchronous requests, but relies for manipulation of its metadata on
- * synchronous bdrv_read/write that doesn't trigger any callbacks.
- *
- * However, these functions are often emulated using AIO which means that AIO
- * callbacks must be run - but at the same time we must not run callbacks of
- * other requests as they might start to modify metadata and corrupt the
- * internal state of the caller of bdrv_read/write.
- *
- * To achieve the desired semantics we switch into a new AsyncContext.
- * Callbacks must only be run if they belong to the current AsyncContext.
- * Otherwise they need to be queued until their own context is active again.
- * This is how you can make qemu_aio_wait() wait only for your own callbacks.
- *
- * The AsyncContexts form a stack. When you leave a AsyncContexts, you always
- * return to the old ("parent") context.
- */
-struct AsyncContext {
- /* Consecutive number of the AsyncContext (position in the stack) */
- int id;
-
- /* Anchor of the list of Bottom Halves belonging to the context */
- struct QEMUBH *first_bh;
-
- /* Link to parent context */
- struct AsyncContext *parent;
-};
-
-/* The currently active AsyncContext */
-static struct AsyncContext *async_context = &(struct AsyncContext) { 0 };
-
-/*
- * Enter a new AsyncContext. Already scheduled Bottom Halves and AIO callbacks
- * won't be called until this context is left again.
- */
-void async_context_push(void)
-{
- struct AsyncContext *new = qemu_mallocz(sizeof(*new));
- new->parent = async_context;
- new->id = async_context->id + 1;
- async_context = new;
-}
-
-/* Run queued AIO completions and destroy Bottom Half */
-static void bh_run_aio_completions(void *opaque)
-{
- QEMUBH **bh = opaque;
- qemu_bh_delete(*bh);
- qemu_free(bh);
- qemu_aio_process_queue();
-}
-/*
- * Leave the currently active AsyncContext. All Bottom Halves belonging to the
- * old context are executed before changing the context.
- */
-void async_context_pop(void)
-{
- struct AsyncContext *old = async_context;
- QEMUBH **bh;
-
- /* Flush the bottom halves, we don't want to lose them */
- while (qemu_bh_poll());
-
- /* Switch back to the parent context */
- async_context = async_context->parent;
- qemu_free(old);
-
- if (async_context == NULL) {
- abort();
- }
-
- /* Schedule BH to run any queued AIO completions as soon as possible */
- bh = qemu_malloc(sizeof(*bh));
- *bh = qemu_bh_new(bh_run_aio_completions, bh);
- qemu_bh_schedule(*bh);
-}
-
-/*
- * Returns the ID of the currently active AsyncContext
- */
-int get_async_context_id(void)
-{
- return async_context->id;
-}
+#include "block/aio.h"
+#include "block/thread-pool.h"
+#include "qemu/main-loop.h"
+#include "qemu/atomic.h"
/***********************************************************/
/* bottom halves (can be seen as timers which expire ASAP) */
struct QEMUBH {
+ AioContext *ctx;
QEMUBHFunc *cb;
void *opaque;
- int scheduled;
- int idle;
- int deleted;
QEMUBH *next;
+ bool scheduled;
+ bool idle;
+ bool deleted;
};
-QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
+QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
{
QEMUBH *bh;
- bh = qemu_mallocz(sizeof(QEMUBH));
+ bh = g_new0(QEMUBH, 1);
+ bh->ctx = ctx;
bh->cb = cb;
bh->opaque = opaque;
- bh->next = async_context->first_bh;
- async_context->first_bh = bh;
+ qemu_mutex_lock(&ctx->bh_lock);
+ bh->next = ctx->first_bh;
+ /* Make sure that the members are ready before putting bh into list */
+ smp_wmb();
+ ctx->first_bh = bh;
+ qemu_mutex_unlock(&ctx->bh_lock);
return bh;
}
-int qemu_bh_poll(void)
+/* Multiple occurrences of aio_bh_poll cannot be called concurrently */
+int aio_bh_poll(AioContext *ctx)
{
QEMUBH *bh, **bhp, *next;
int ret;
+ ctx->walking_bh++;
+
ret = 0;
- for (bh = async_context->first_bh; bh; bh = next) {
+ for (bh = ctx->first_bh; bh; bh = next) {
+ /* Make sure that fetching bh happens before accessing its members */
+ smp_read_barrier_depends();
next = bh->next;
if (!bh->deleted && bh->scheduled) {
bh->scheduled = 0;
+ /* Paired with write barrier in bh schedule to ensure reading for
+ * idle & callbacks coming after bh's scheduling.
+ */
+ smp_rmb();
if (!bh->idle)
ret = 1;
bh->idle = 0;
}
}
+ ctx->walking_bh--;
+
/* remove deleted bhs */
- bhp = &async_context->first_bh;
- while (*bhp) {
- bh = *bhp;
- if (bh->deleted) {
- *bhp = bh->next;
- qemu_free(bh);
- } else
- bhp = &bh->next;
+ if (!ctx->walking_bh) {
+ qemu_mutex_lock(&ctx->bh_lock);
+ bhp = &ctx->first_bh;
+ while (*bhp) {
+ bh = *bhp;
+ if (bh->deleted) {
+ *bhp = bh->next;
+ g_free(bh);
+ } else {
+ bhp = &bh->next;
+ }
+ }
+ qemu_mutex_unlock(&ctx->bh_lock);
}
return ret;
{
if (bh->scheduled)
return;
- bh->scheduled = 1;
bh->idle = 1;
+ /* Make sure that idle & any writes needed by the callback are done
+ * before the locations are read in the aio_bh_poll.
+ */
+ smp_wmb();
+ bh->scheduled = 1;
}
void qemu_bh_schedule(QEMUBH *bh)
{
+ AioContext *ctx;
+
if (bh->scheduled)
return;
- bh->scheduled = 1;
+ ctx = bh->ctx;
bh->idle = 0;
- /* stop the currently executing CPU to execute the BH ASAP */
- qemu_notify_event();
+ /* Make sure that:
+ * 1. idle & any writes needed by the callback are done before the
+ * locations are read in the aio_bh_poll.
+ * 2. ctx is loaded before scheduled is set and the callback has a chance
+ * to execute.
+ */
+ smp_mb();
+ bh->scheduled = 1;
+ aio_notify(ctx);
}
+
+/* This func is async.
+ */
void qemu_bh_cancel(QEMUBH *bh)
{
bh->scheduled = 0;
}
+/* This func is async.The bottom half will do the delete action at the finial
+ * end.
+ */
void qemu_bh_delete(QEMUBH *bh)
{
bh->scheduled = 0;
bh->deleted = 1;
}
-void qemu_bh_update_timeout(int *timeout)
+int64_t
+aio_compute_timeout(AioContext *ctx)
{
+ int64_t deadline;
+ int timeout = -1;
QEMUBH *bh;
- for (bh = async_context->first_bh; bh; bh = bh->next) {
+ for (bh = ctx->first_bh; bh; bh = bh->next) {
if (!bh->deleted && bh->scheduled) {
if (bh->idle) {
/* idle bottom halves will be polled at least
* every 10ms */
- *timeout = MIN(10, *timeout);
+ timeout = 10000000;
} else {
/* non-idle bottom halves will be executed
* immediately */
- *timeout = 0;
- break;
+ return 0;
}
}
}
+
+ deadline = timerlistgroup_deadline_ns(&ctx->tlg);
+ if (deadline == 0) {
+ return 0;
+ } else {
+ return qemu_soonest_timeout(timeout, deadline);
+ }
}
+static gboolean
+aio_ctx_prepare(GSource *source, gint *timeout)
+{
+ AioContext *ctx = (AioContext *) source;
+
+ /* We assume there is no timeout already supplied */
+ *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
+
+ if (aio_prepare(ctx)) {
+ *timeout = 0;
+ }
+
+ return *timeout == 0;
+}
+
+static gboolean
+aio_ctx_check(GSource *source)
+{
+ AioContext *ctx = (AioContext *) source;
+ QEMUBH *bh;
+
+ for (bh = ctx->first_bh; bh; bh = bh->next) {
+ if (!bh->deleted && bh->scheduled) {
+ return true;
+ }
+ }
+ return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
+}
+
+static gboolean
+aio_ctx_dispatch(GSource *source,
+ GSourceFunc callback,
+ gpointer user_data)
+{
+ AioContext *ctx = (AioContext *) source;
+
+ assert(callback == NULL);
+ aio_dispatch(ctx);
+ return true;
+}
+
+static void
+aio_ctx_finalize(GSource *source)
+{
+ AioContext *ctx = (AioContext *) source;
+
+ thread_pool_free(ctx->thread_pool);
+ aio_set_event_notifier(ctx, &ctx->notifier, NULL);
+ event_notifier_cleanup(&ctx->notifier);
+ rfifolock_destroy(&ctx->lock);
+ qemu_mutex_destroy(&ctx->bh_lock);
+ g_array_free(ctx->pollfds, TRUE);
+ timerlistgroup_deinit(&ctx->tlg);
+}
+
+static GSourceFuncs aio_source_funcs = {
+ aio_ctx_prepare,
+ aio_ctx_check,
+ aio_ctx_dispatch,
+ aio_ctx_finalize
+};
+
+GSource *aio_get_g_source(AioContext *ctx)
+{
+ g_source_ref(&ctx->source);
+ return &ctx->source;
+}
+
+ThreadPool *aio_get_thread_pool(AioContext *ctx)
+{
+ if (!ctx->thread_pool) {
+ ctx->thread_pool = thread_pool_new(ctx);
+ }
+ return ctx->thread_pool;
+}
+
+void aio_set_dispatching(AioContext *ctx, bool dispatching)
+{
+ ctx->dispatching = dispatching;
+ if (!dispatching) {
+ /* Write ctx->dispatching before reading e.g. bh->scheduled.
+ * Optimization: this is only needed when we're entering the "unsafe"
+ * phase where other threads must call event_notifier_set.
+ */
+ smp_mb();
+ }
+}
+
+void aio_notify(AioContext *ctx)
+{
+ /* Write e.g. bh->scheduled before reading ctx->dispatching. */
+ smp_mb();
+ if (!ctx->dispatching) {
+ event_notifier_set(&ctx->notifier);
+ }
+}
+
+static void aio_timerlist_notify(void *opaque)
+{
+ aio_notify(opaque);
+}
+
+static void aio_rfifolock_cb(void *opaque)
+{
+ /* Kick owner thread in case they are blocked in aio_poll() */
+ aio_notify(opaque);
+}
+
+AioContext *aio_context_new(Error **errp)
+{
+ int ret;
+ AioContext *ctx;
+ ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
+ ret = event_notifier_init(&ctx->notifier, false);
+ if (ret < 0) {
+ g_source_destroy(&ctx->source);
+ error_setg_errno(errp, -ret, "Failed to initialize event notifier");
+ return NULL;
+ }
+ aio_set_event_notifier(ctx, &ctx->notifier,
+ (EventNotifierHandler *)
+ event_notifier_test_and_clear);
+ ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
+ ctx->thread_pool = NULL;
+ qemu_mutex_init(&ctx->bh_lock);
+ rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
+ timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
+
+ return ctx;
+}
+
+void aio_context_ref(AioContext *ctx)
+{
+ g_source_ref(&ctx->source);
+}
+
+void aio_context_unref(AioContext *ctx)
+{
+ g_source_unref(&ctx->source);
+}
+
+void aio_context_acquire(AioContext *ctx)
+{
+ rfifolock_lock(&ctx->lock);
+}
+
+void aio_context_release(AioContext *ctx)
+{
+ rfifolock_unlock(&ctx->lock);
+}
projects / qemu.git / blobdiff