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authorPaolo Bonzini <pbonzini@redhat.com>2019-04-09 14:28:23 +0200
committerStefan Hajnoczi <stefanha@redhat.com>2019-05-10 10:53:21 +0100
commit993ed89f35bf2b2250727667f2a640b3c232259f (patch)
treef53e1f9d206d95153bde411252cb2f23617fa919 /util
parent118f99442d3a8ce47836978cddd9206ac2d2b001 (diff)
aio-posix: ensure poll mode is left when aio_notify is called
With aio=thread, adaptive polling makes latency worse rather than better, because it delays the execution of the ThreadPool's completion bottom half. event_notifier_poll() does run while polling, detecting that a bottom half was scheduled by a worker thread, but because ctx->notifier is explicitly ignored in run_poll_handlers_once(), scheduling the BH does not count as making progress and run_poll_handlers() keeps running. Fix this by recomputing the deadline after *timeout could have changed. With this change, ThreadPool still cannot participate in polling but at least it does not suffer from extra latency. Reported-by: Sergio Lopez <slp@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-id: 20190409122823.12416-1-pbonzini@redhat.com Cc: Stefan Hajnoczi <stefanha@gmail.com> Cc: Kevin Wolf <kwolf@redhat.com> Cc: qemu-block@nongnu.org Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <1553692145-86728-1-git-send-email-pbonzini@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20190409122823.12416-1-pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'util')
-rw-r--r--util/aio-posix.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/util/aio-posix.c b/util/aio-posix.c
index 6fbfa7924f..db11021287 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -519,6 +519,10 @@ static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout)
if (!node->deleted && node->io_poll &&
aio_node_check(ctx, node->is_external) &&
node->io_poll(node->opaque)) {
+ /*
+ * Polling was successful, exit try_poll_mode immediately
+ * to adjust the next polling time.
+ */
*timeout = 0;
if (node->opaque != &ctx->notifier) {
progress = true;
@@ -558,8 +562,9 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout)
do {
progress = run_poll_handlers_once(ctx, timeout);
elapsed_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start_time;
- } while (!progress && elapsed_time < max_ns
- && !atomic_read(&ctx->poll_disable_cnt));
+ max_ns = qemu_soonest_timeout(*timeout, max_ns);
+ assert(!(max_ns && progress));
+ } while (elapsed_time < max_ns && !atomic_read(&ctx->poll_disable_cnt));
/* If time has passed with no successful polling, adjust *timeout to
* keep the same ending time.
@@ -585,8 +590,7 @@ static bool run_poll_handlers(AioContext *ctx, int64_t max_ns, int64_t *timeout)
*/
static bool try_poll_mode(AioContext *ctx, int64_t *timeout)
{
- /* See qemu_soonest_timeout() uint64_t hack */
- int64_t max_ns = MIN((uint64_t)*timeout, (uint64_t)ctx->poll_ns);
+ int64_t max_ns = qemu_soonest_timeout(*timeout, ctx->poll_ns);
if (max_ns && !atomic_read(&ctx->poll_disable_cnt)) {
poll_set_started(ctx, true);