Re: [RFC PATCH] epoll: Add synchronous wakeup support for ep_poll_callback

[Brian Geffon <bgeffon@google.com>]

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@vger.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@vger.kernel.org

> 
> 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