linux-kernel - Re: [RFC PATCH] epoll: Add synchronous wakeup support for ep_poll

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Message-ID: <CADyq12y=MGzcvemZTVVGN4yhzr2ihr96OB-Vpg0yvrtrewnFDg@mail.gmail.com>
Date: Tue, 17 Dec 2024 09:30:51 -0500
From: Brian Geffon <bgeffon@...gle.com>
To: Greg KH <gregkh@...uxfoundation.org>, "# v4 . 10+" <stable@...r.kernel.org>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, Christian Brauner <brauner@...nel.org>, jack@...e.cz, 
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, cmllamas@...gle.com, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ke.wang@...soc.com, jing.xia@...soc.com, xuewen.yan94@...il.com, 
	viro@...iv.linux.org.uk, mingo@...hat.com, peterz@...radead.org, 
	juri.lelli@...hat.com, vincent.guittot@...aro.org, lizeb@...gle.com
Subject: Re: [RFC PATCH] epoll: Add synchronous wakeup support for ep_poll_callback

On Thu, Dec 12, 2024 at 12:14 PM Brian Geffon <bgeffon@...gle.com> wrote:
>
> On Wed, Oct 16, 2024 at 03:05:38PM -0400, Brian Geffon wrote:
> > On Wed, Oct 16, 2024 at 03:10:34PM +0200, Christian Brauner wrote:
> > > On Fri, 26 Apr 2024 16:05:48 +0800, Xuewen Yan wrote:
> > > > Now, the epoll only use wake_up() interface to wake up task.
> > > > However, sometimes, there are epoll users which want to use
> > > > the synchronous wakeup flag to hint the scheduler, such as
> > > > Android binder driver.
> > > > So add a wake_up_sync() define, and use the wake_up_sync()
> > > > when the sync is true in ep_poll_callback().
> > > >
> > > > [...]
> > >
> > > Applied to the vfs.misc branch of the vfs/vfs.git tree.
> > > Patches in the vfs.misc branch should appear in linux-next soon.
> > >
> > > Please report any outstanding bugs that were missed during review in a
> > > new review to the original patch series allowing us to drop it.
> > >
> > > It's encouraged to provide Acked-bys and Reviewed-bys even though the
> > > patch has now been applied. If possible patch trailers will be updated.
> > >
> > > Note that commit hashes shown below are subject to change due to rebase,
> > > trailer updates or similar. If in doubt, please check the listed branch.
> > >
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> > > branch: vfs.misc
> >
> > This is a bug that's been present for all of time, so I think we should:
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Cc: stable@...r.kernel.org
>
> This is in as 900bbaae ("epoll: Add synchronous wakeup support for
> ep_poll_callback"). How do maintainers feel about:
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@...r.kernel.org

Dear stable maintainers, this fixes a bug goes all the way back and
beyond Linux 2.6.12-rc2. Can you please add this commit to the stable
releases?

commit 900bbaae67e980945dec74d36f8afe0de7556d5a upstream.

>
> >
> > I sent a patch which adds a benchmark for nonblocking pipes using epoll:
> > https://lore.kernel.org/lkml/20241016190009.866615-1-bgeffon@google.com/
> >
> > Using this new benchmark I get the following results without this fix
> > and with this fix:
> >
> > $ tools/perf/perf bench sched pipe -n
> > # Running 'sched/pipe' benchmark:
> > # Executed 1000000 pipe operations between two processes
> >
> >      Total time: 12.194 [sec]
> >
> >       12.194376 usecs/op
> >           82005 ops/sec
> >
> >
> > $ tools/perf/perf bench sched pipe -n
> > # Running 'sched/pipe' benchmark:
> > # Executed 1000000 pipe operations between two processes
> >
> >      Total time: 9.229 [sec]
> >
> >        9.229738 usecs/op
> >          108345 ops/sec
> >
> > >
> > > [1/1] epoll: Add synchronous wakeup support for ep_poll_callback
> > >       https://git.kernel.org/vfs/vfs/c/2ce0e17660a7
>
> Thanks,
> Brian
>

 Thanks,
 Brian