Re: [PATCH RESEND v4] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode

[Roman Penyaev]

On 2019-09-28 04:29, Andrew Morton wrote:
> On Wed, 25 Sep 2019 09:56:03 +0800 hev <r@xxxxxx> wrote:
>
> > From: Heiher <r@xxxxxx>
> >
> > Take the case where we have:
> >
> >         t0
> >          | (ew)
> >         e0
> >          | (et)
> >         e1
> >          | (lt)
> >         s0
> >
> > t0: thread 0
> > e0: epoll fd 0
> > e1: epoll fd 1
> > s0: socket fd 0
> > ew: epoll_wait
> > et: edge-trigger
> > lt: level-trigger
> >
> > We only need to wakeup nested epoll fds if something has been queued 
> > to the
> > overflow list, since the ep_poll() traverses the rdllist during 
> > recursive poll
> > and thus events on the overflow list may not be visible yet.
> >
> > Test code:
>
> Look sane to me.  Do you have any performance testing results which
> show a benefit?
>
> epoll maintainership isn't exactly a hive of activity nowadays :(
> Roman, would you please have time to review this?

Yes, I can revisit this once more next week.

Heiher, mind to prepare a patchset with your test suit and make it a 
part
of kselftest?  I hope nobody has any objections.

--
Roman