Commit 70232b5253 ("aio-posix: Don't count ctx->notifier as progress when
2018-08-15), by not reporting progress, causes aio_poll to execute the
system call when polling succeeds because of ctx->notifier.  This introduces
latency before the call to aio_bh_poll() and negates the advantages of
polling, unfortunately.

The fix builds on the previous patch, separating the effect of polling on
the timeout from the progress reported to aio_poll().  ctx->notifier
does zero the timeout, causing the caller to skip the system call,
but it does not report progress, so that the bug fix of commit 70232b5253
still stands.

Fixes: 70232b5253a3c4e03ed1ac47ef9246a8ac66c6fa
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 util/aio-posix.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/util/aio-posix.c b/util/aio-posix.c
index 21d8987179..efa79b9e62 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -498,10 +498,11 @@ static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout)
     QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
         if (!node->deleted && node->io_poll &&
             aio_node_check(ctx, node->is_external) &&
-            node->io_poll(node->opaque) &&
-            node->opaque != &ctx->notifier) {
+            node->io_poll(node->opaque)) {
             *timeout = 0;
-            progress = true;
+            if (node->opaque != &ctx->notifier) {
+                progress = true;
+            }
         }
 
         /* Caller handles freeing deleted nodes.  Don't do it here. */
-- 
2.17.1

On Wed, 09/12 19:10, Paolo Bonzini wrote:
> Commit 70232b5253 ("aio-posix: Don't count ctx->notifier as progress when
> 2018-08-15), by not reporting progress, causes aio_poll to execute the
> system call when polling succeeds because of ctx->notifier.  This introduces
> latency before the call to aio_bh_poll() and negates the advantages of
> polling, unfortunately.
> 
> The fix builds on the previous patch, separating the effect of polling on
> the timeout from the progress reported to aio_poll().  ctx->notifier
> does zero the timeout, causing the caller to skip the system call,
> but it does not report progress, so that the bug fix of commit 70232b5253
> still stands.
> 
> Fixes: 70232b5253a3c4e03ed1ac47ef9246a8ac66c6fa
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  util/aio-posix.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/util/aio-posix.c b/util/aio-posix.c
> index 21d8987179..efa79b9e62 100644
> --- a/util/aio-posix.c
> +++ b/util/aio-posix.c
> @@ -498,10 +498,11 @@ static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout)
>      QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
>          if (!node->deleted && node->io_poll &&
>              aio_node_check(ctx, node->is_external) &&
> -            node->io_poll(node->opaque) &&
> -            node->opaque != &ctx->notifier) {
> +            node->io_poll(node->opaque)) {
>              *timeout = 0;
> -            progress = true;
> +            if (node->opaque != &ctx->notifier) {
> +                progress = true;
> +            }
>          }
>  
>          /* Caller handles freeing deleted nodes.  Don't do it here. */
> -- 
> 2.17.1
> 

Reviewed-by: Fam Zheng <famz@redhat.com>