@@ -361,12 +361,13 @@ void aio_set_event_notifier_poll(AioContext *ctx,
(IOHandler *)io_poll_end);
}
-static void poll_set_started(AioContext *ctx, bool started)
+static bool poll_set_started(AioContext *ctx, bool started)
{
AioHandler *node;
+ bool progress = false;
if (started == ctx->poll_started) {
- return;
+ return false;
}
ctx->poll_started = started;
@@ -388,8 +389,15 @@ static void poll_set_started(AioContext *ctx, bool started)
if (fn) {
fn(node->opaque);
}
+
+ /* Poll one last time in case ->io_poll_end() raced with the event */
+ if (!started) {
+ progress = node->io_poll(node->opaque) || progress;
+ }
}
qemu_lockcnt_dec(&ctx->list_lock);
+
+ return progress;
}
@@ -670,12 +678,12 @@ static bool try_poll_mode(AioContext *ctx, int64_t *timeout)
}
}
- poll_set_started(ctx, false);
+ if (poll_set_started(ctx, false)) {
+ *timeout = 0;
+ return true;
+ }
- /* Even if we don't run busy polling, try polling once in case it can make
- * progress and the caller will be able to avoid ppoll(2)/epoll_wait(2).
- */
- return run_poll_handlers_once(ctx, timeout);
+ return false;
}
bool aio_poll(AioContext *ctx, bool blocking)
One iteration of polling is always performed even when polling is disabled. This is done because: 1. Userspace polling is cheaper than making a syscall. We might get lucky. 2. We must poll once more after polling has stopped in case an event occurred while stopping polling. However, there are downsides: 1. Polling becomes a bottleneck when the number of event sources is very high. It's more efficient to monitor fds in that case. 2. A high-frequency polling event source can starve non-polling event sources because ppoll(2)/epoll(7) is never invoked. This patch removes the forced polling iteration so that poll_ns=0 really means no polling. IOPS increases from 10k to 60k when the guest has 100 virtio-blk-pci,num-queues=32 devices and 1 virtio-blk-pci,num-queues=1 device because the large number of event sources being polled slows down the event loop. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Link: https://lore.kernel.org/r/20200305170806.1313245-2-stefanha@redhat.com Message-Id: <20200305170806.1313245-2-stefanha@redhat.com> --- util/aio-posix.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-)