@@ -464,9 +464,6 @@ static bool remove_idle_poll_handlers(AioContext *ctx, int64_t now)
*
* Polls for a given time.
*
- * Note that ctx->notify_me must be non-zero so this function can detect
- * aio_notify().
- *
* Note that the caller must have incremented ctx->list_lock.
*
* Returns: true if progress was made, false otherwise
@@ -476,7 +473,6 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout)
bool progress;
int64_t start_time, elapsed_time;
- assert(ctx->notify_me);
assert(qemu_lockcnt_count(&ctx->list_lock) > 0);
trace_run_poll_handlers_begin(ctx, max_ns, *timeout);
@@ -520,8 +516,6 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout)
* @timeout: timeout for blocking wait, computed by the caller and updated if
* polling succeeds.
*
- * ctx->notify_me must be non-zero so this function can detect aio_notify().
- *
* Note that the caller must have incremented ctx->list_lock.
*
* Returns: true if progress was made, false otherwise
@@ -566,23 +560,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
*/
assert(in_aio_context_home_thread(ctx));
- /* aio_notify can avoid the expensive event_notifier_set if
- * everything (file descriptors, bottom halves, timers) will
- * be re-evaluated before the next blocking poll(). This is
- * already true when aio_poll is called with blocking == false;
- * if blocking == true, it is only true after poll() returns,
- * so disable the optimization now.
- */
- if (blocking) {
- atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2);
- /*
- * Write ctx->notify_me before computing the timeout
- * (reading bottom half flags, etc.). Pairs with
- * smp_mb in aio_notify().
- */
- smp_mb();
- }
-
qemu_lockcnt_inc(&ctx->list_lock);
if (ctx->poll_max_ns) {
@@ -597,15 +574,38 @@ bool aio_poll(AioContext *ctx, bool blocking)
* system call---a single round of run_poll_handlers_once suffices.
*/
if (timeout || ctx->fdmon_ops->need_wait(ctx)) {
+ /*
+ * aio_notify can avoid the expensive event_notifier_set if
+ * everything (file descriptors, bottom halves, timers) will
+ * be re-evaluated before the next blocking poll(). This is
+ * already true when aio_poll is called with blocking == false;
+ * if blocking == true, it is only true after poll() returns,
+ * so disable the optimization now.
+ */
+ if (timeout) {
+ atomic_set(&ctx->notify_me, atomic_read(&ctx->notify_me) + 2);
+ /*
+ * Write ctx->notify_me before computing the timeout
+ * (reading bottom half flags, etc.). Pairs with
+ * smp_mb in aio_notify().
+ */
+ smp_mb();
+
+ /* Check again in case a shorter timer was added */
+ timeout = qemu_soonest_timeout(timeout, aio_compute_timeout(ctx));
+ }
+
ret = ctx->fdmon_ops->wait(ctx, &ready_list, timeout);
- }
- if (blocking) {
- /* Finish the poll before clearing the flag. */
- atomic_store_release(&ctx->notify_me, atomic_read(&ctx->notify_me) - 2);
- aio_notify_accept(ctx);
+ if (timeout) {
+ /* Finish the poll before clearing the flag. */
+ atomic_store_release(&ctx->notify_me,
+ atomic_read(&ctx->notify_me) - 2);
+ }
}
+ aio_notify_accept(ctx);
+
/* Adjust polling time */
if (ctx->poll_max_ns) {
int64_t block_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start;
Polling only monitors the ctx->notified field and does not need the ctx->notifier EventNotifier to be signalled. Keep ctx->aio_notify_me disabled while polling to avoid unnecessary EventNotifier syscalls. This optimization improves virtio-blk 4KB random read performance by 18%. The following results are with an IOThread and the null-co block driver: Test IOPS Error Before 244518.62 ± 1.20% After 290706.11 ± 0.44% Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- util/aio-posix.c | 56 ++++++++++++++++++++++++------------------------ 1 file changed, 28 insertions(+), 28 deletions(-)