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![Stefan Hajnoczi](/assets/img/avatar_default.png)
This patch drops a special case where aio_poll(ctx, true) returns false instead of blocking if no file descriptors are waiting on I/O. Now it is possible to block in aio_poll() to wait for aio_notify(). This change eliminates busy waiting. bdrv_drain_all() used to rely on busy waiting to completed throttled I/O requests but this is no longer required so we can simplify aio_poll(). Note that aio_poll() still returns false when aio_notify() was used. In other words, stopping a blocking aio_poll() wait is not considered making progress. Adjust test-aio /aio/bh/callback-delete/one which assumed aio_poll(ctx, true) would immediately return false instead of blocking. Reviewed-by: Alex Bligh <alex@alex.org.uk> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
224 lines
6 KiB
C
224 lines
6 KiB
C
/*
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* QEMU aio implementation
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*
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* Copyright IBM Corp., 2008
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* Copyright Red Hat Inc., 2012
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*
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* Authors:
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* Anthony Liguori <aliguori@us.ibm.com>
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* Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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* Contributions after 2012-01-13 are licensed under the terms of the
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* GNU GPL, version 2 or (at your option) any later version.
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*/
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#include "qemu-common.h"
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#include "block/block.h"
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#include "qemu/queue.h"
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#include "qemu/sockets.h"
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struct AioHandler {
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EventNotifier *e;
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EventNotifierHandler *io_notify;
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GPollFD pfd;
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int deleted;
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QLIST_ENTRY(AioHandler) node;
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};
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void aio_set_event_notifier(AioContext *ctx,
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EventNotifier *e,
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EventNotifierHandler *io_notify)
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{
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AioHandler *node;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (node->e == e && !node->deleted) {
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break;
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}
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}
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/* Are we deleting the fd handler? */
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if (!io_notify) {
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if (node) {
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g_source_remove_poll(&ctx->source, &node->pfd);
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/* If the lock is held, just mark the node as deleted */
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if (ctx->walking_handlers) {
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node->deleted = 1;
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node->pfd.revents = 0;
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} else {
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/* Otherwise, delete it for real. We can't just mark it as
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* deleted because deleted nodes are only cleaned up after
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* releasing the walking_handlers lock.
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*/
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QLIST_REMOVE(node, node);
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g_free(node);
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}
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}
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} else {
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if (node == NULL) {
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/* Alloc and insert if it's not already there */
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node = g_malloc0(sizeof(AioHandler));
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node->e = e;
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node->pfd.fd = (uintptr_t)event_notifier_get_handle(e);
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node->pfd.events = G_IO_IN;
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QLIST_INSERT_HEAD(&ctx->aio_handlers, node, node);
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g_source_add_poll(&ctx->source, &node->pfd);
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}
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/* Update handler with latest information */
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node->io_notify = io_notify;
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}
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aio_notify(ctx);
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}
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bool aio_pending(AioContext *ctx)
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{
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AioHandler *node;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (node->pfd.revents && node->io_notify) {
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return true;
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}
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}
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return false;
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}
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bool aio_poll(AioContext *ctx, bool blocking)
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{
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AioHandler *node;
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HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
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bool progress;
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int count;
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int timeout;
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progress = false;
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/*
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* If there are callbacks left that have been queued, we need to call then.
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* Do not call select in this case, because it is possible that the caller
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* does not need a complete flush (as is the case for qemu_aio_wait loops).
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*/
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if (aio_bh_poll(ctx)) {
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blocking = false;
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progress = true;
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}
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/* Run timers */
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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/*
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* Then dispatch any pending callbacks from the GSource.
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*
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* We have to walk very carefully in case qemu_aio_set_fd_handler is
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* called while we're walking.
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*/
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node = QLIST_FIRST(&ctx->aio_handlers);
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while (node) {
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AioHandler *tmp;
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ctx->walking_handlers++;
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if (node->pfd.revents && node->io_notify) {
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node->pfd.revents = 0;
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node->io_notify(node->e);
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/* aio_notify() does not count as progress */
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if (node->e != &ctx->notifier) {
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progress = true;
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}
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}
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tmp = node;
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node = QLIST_NEXT(node, node);
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ctx->walking_handlers--;
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if (!ctx->walking_handlers && tmp->deleted) {
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QLIST_REMOVE(tmp, node);
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g_free(tmp);
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}
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}
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if (progress && !blocking) {
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return true;
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}
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ctx->walking_handlers++;
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/* fill fd sets */
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count = 0;
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QLIST_FOREACH(node, &ctx->aio_handlers, node) {
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if (!node->deleted && node->io_notify) {
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events[count++] = event_notifier_get_handle(node->e);
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}
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}
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ctx->walking_handlers--;
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/* wait until next event */
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while (count > 0) {
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int ret;
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timeout = blocking ?
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qemu_timeout_ns_to_ms(timerlistgroup_deadline_ns(&ctx->tlg)) : 0;
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ret = WaitForMultipleObjects(count, events, FALSE, timeout);
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/* if we have any signaled events, dispatch event */
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if ((DWORD) (ret - WAIT_OBJECT_0) >= count) {
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break;
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}
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blocking = false;
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/* we have to walk very carefully in case
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* qemu_aio_set_fd_handler is called while we're walking */
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node = QLIST_FIRST(&ctx->aio_handlers);
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while (node) {
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AioHandler *tmp;
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ctx->walking_handlers++;
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if (!node->deleted &&
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event_notifier_get_handle(node->e) == events[ret - WAIT_OBJECT_0] &&
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node->io_notify) {
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node->io_notify(node->e);
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/* aio_notify() does not count as progress */
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if (node->e != &ctx->notifier) {
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progress = true;
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}
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}
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tmp = node;
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node = QLIST_NEXT(node, node);
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ctx->walking_handlers--;
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if (!ctx->walking_handlers && tmp->deleted) {
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QLIST_REMOVE(tmp, node);
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g_free(tmp);
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}
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}
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/* Try again, but only call each handler once. */
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events[ret - WAIT_OBJECT_0] = events[--count];
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}
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if (blocking) {
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/* Run the timers a second time. We do this because otherwise aio_wait
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* will not note progress - and will stop a drain early - if we have
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* a timer that was not ready to run entering g_poll but is ready
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* after g_poll. This will only do anything if a timer has expired.
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*/
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progress |= timerlistgroup_run_timers(&ctx->tlg);
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}
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return progress;
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}
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