Re: [Qemu-devel] [PATCH] linux-aio: Cancel BH if not needed

[Paolo Bonzini <pbonzini@redhat.com>]

On 15/06/2016 13:16, Kevin Wolf wrote:
> linux-aio uses a BH in order to make sure that the remaining completions
> are processed even in nested event loops of completion callbacks in
> order to avoid deadlocks.
> 
> There is no need, however, to have the BH overhead for the first call
> into qemu_laio_completion_bh() or after all pending completions have
> already been processed. Therefore, this patch calls directly into
> qemu_laio_completion_bh() in qemu_laio_completion_cb() and cancels
> the BH after qemu_laio_completion_bh() has processed all pending
> completions.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/linux-aio.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/block/linux-aio.c b/block/linux-aio.c
> index fe7cece..e468960 100644
> --- a/block/linux-aio.c
> +++ b/block/linux-aio.c
> @@ -149,6 +149,8 @@ static void qemu_laio_completion_bh(void *opaque)
>      if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
>          ioq_submit(s);
>      }
> +
> +    qemu_bh_cancel(s->completion_bh);
>  }
>  
>  static void qemu_laio_completion_cb(EventNotifier *e)
> @@ -156,7 +158,7 @@ static void qemu_laio_completion_cb(EventNotifier *e)
>      LinuxAioState *s = container_of(e, LinuxAioState, e);
>  
>      if (event_notifier_test_and_clear(&s->e)) {
> -        qemu_bh_schedule(s->completion_bh);
> +        qemu_laio_completion_bh(s);
>      }
>  }
>  
> 

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