Re: [RFC v1] util/aio: Keep notification disabled as much as possible

[Chao Gao <chao.gao@intel.com>]

On Thu, Jul 07, 2022 at 10:04:23AM +0100, Stefan Hajnoczi wrote:
>
>Does this patch solve the issue? The idea is to defer
>poll_set_started(false) for as long as possible.

Good idea! It is straightforward.

>
>diff --git a/util/aio-posix.c b/util/aio-posix.c
>index 731f3826c0..536f8b2534 100644
>--- a/util/aio-posix.c
>+++ b/util/aio-posix.c
>@@ -591,12 +591,6 @@ static bool try_poll_mode(AioContext *ctx, AioHandlerList *ready_list,
>             return true;
>         }
>     }
>-
>-    if (poll_set_started(ctx, ready_list, false)) {
>-        *timeout = 0;
>-        return true;
>-    }
>-
>     return false;
> }
>
>@@ -657,6 +651,11 @@ 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)) {
>+        if (poll_set_started(ctx, &ready_list, false)) {
>+            timeout = 0;
>+            progress = true;

In this case, is it ok to skip the call of ->wait() below? If yes, maybe put
the call in the "else" path.

>+        }
>+
>         ctx->fdmon_ops->wait(ctx, &ready_list, timeout);
>     }
>

Anyway,
Reviewed-by: Chao Gao <chao.gao@intel.com>

And my tests show your change works well. The number of notifications is
significantly reduced from ~80K/s to tens.

Tested-by: Chao Gao <chao.gao@intel.com>