Re: [PATCH v3 0/3] aio-posix: keep aio_notify_me disabled during polling

[Paolo Bonzini]

On 06/08/20 15:17, Stefan Hajnoczi wrote:
> v3:
>  * Use smp_wmb() in aio_notify_accept() [Paolo]
>  * Flatten if statement in aio_poll() [Paolo]
> 
> v2:
>  * Added smp_mb() in aio_notify_accept() [Paolo]
>  * Added comments about memory barrier pairing [Paolo]
>  * Eliminated extra aio_compute_timeout() before calling ppoll()
> 
> This patch series eliminates ctx->notifier EventNotifier activity when
> aio_poll() is in polling mode. There is no need to use the EventNotifier since
> a polling handler can detect that aio_notify() has been called by monitoring a
> field in memory instead.
> 
> Optimizing out the EventNotifier calls improves null-co random read 4KB
> iodepth=1 IOPS by 18%.
> 
> I have not modified docs/spin/aio_notify*.promela because I'm not familiar 
> with
> the SPIN model checker.
> 
> Stefan Hajnoczi (3):
>   async: rename event_notifier_dummy_cb/poll()
>   async: always set ctx->notified in aio_notify()
>   aio-posix: keep aio_notify_me disabled during polling
> 
>  util/aio-posix.c | 47 +++++++++++++++++++++++++----------------------
>  util/async.c     | 36 +++++++++++++++++++++++-------------
>  2 files changed, 48 insertions(+), 35 deletions(-)
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

apart from a nit on patch 2.

Paolo