Re: [Qemu-block] [PATCH 2/2] aio: improve aio_poll performance by checking epoll only once

[Yaowei Bai]

On Wed, Sep 14, 2016 at 05:40:17PM +0100, Stefan Hajnoczi wrote:
> On Wed, Sep 14, 2016 at 07:03:39AM -0400, Yaowei Bai wrote:
> > As epoll whether enabled or not is a global setting, we can just
> > check it only once rather than checking it with every node iteration.
> > Through this we can avoid a lot of checks when epoll is not enabled.
> > 
> > Signed-off-by: Yaowei Bai <address@hidden>
> > Reviewed-by: Xiubo Li <address@hidden>
> > ---
> >  aio-posix.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> The commit message says "improve aio_poll performance" but no benchmark
> results were provided.  Therefore I can't take this patch as a
> performance optimization.  I'm still happy to merge the patch since it
> makes the if statement simpler but I'll rename it to "aio-posix: avoid
> unnecessary aio_epoll_enabled() calls".

Sorry for replying late, i just came back from my vacation. And i'd like
to say it's ok for me to rename the commit message. Thank you for doing
it.

> 
> I don't think this patch gives a measurable performance improvement.  If

Yes, i agree with you at this point in consideration of there's no too many
fds to poll at most time.

> you believe otherwise, please post benchmark results.  Please let me
> know what you think.
> 
> Stefan