From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>,
Todd Kjos <tkjos@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Arve Hj??nnev??g <arve@android.com>,
Riley Andrews <riandrews@android.com>,
devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] android: binder: Disable preemption while holding the global binder lock
Date: Sat, 10 Sep 2016 18:37:29 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.20.1609101835360.5560@nanos> (raw)
In-Reply-To: <20160910162210.GK10153@twins.programming.kicks-ass.net>
On Sat, 10 Sep 2016, Peter Zijlstra wrote:
> On Sat, Sep 10, 2016 at 09:16:59AM -0700, Christoph Hellwig wrote:
> > On Thu, Sep 08, 2016 at 09:12:50AM -0700, Todd Kjos wrote:
> > > In Android systems, the display pipeline relies on low
> > > latency binder transactions and is therefore sensitive to
> > > delays caused by contention for the global binder lock.
> > > Jank is siginificantly reduced by disabling preemption
> > > while the global binder lock is held.
> >
> > That's now how preempt_disable is supposed to use. It is for critical
>
> not, that's supposed to be _not_. Just to be absolutely clear, this is
> NOT how you're supposed to use preempt_disable().
>
> > sections that use per-cpu or similar resources.
> >
> > >
> > > Originally-from: Riley Andrews <riandrews@google.com>
> > > Signed-off-by: Todd Kjos <tkjos@google.com>
>
> > > @@ -389,7 +390,11 @@ static int task_get_unused_fd_flags(struct
> > > binder_proc *proc, int flags)
> > > rlim_cur = task_rlimit(proc->tsk, RLIMIT_NOFILE);
> > > unlock_task_sighand(proc->tsk, &irqs);
> > >
> > > - return __alloc_fd(files, 0, rlim_cur, flags);
> > > + preempt_enable_no_resched();
> > > + ret = __alloc_fd(files, 0, rlim_cur, flags);
> > > + preempt_disable();
>
> And the fact that people want to use preempt_enable_no_resched() shows
> that they're absolutely clueless.
>
> This is so broken its not funny.
>
> NAK NAK NAK
Indeed. Sprinkling random preempt_enabe/disable() pairs all over the place
documents clearly that this is tinkering and not proper software
engineering.
NAK from my side as well.
Thanks,
Thomas
next prev parent reply other threads:[~2016-09-10 16:40 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-08 16:12 [PATCH] android: binder: Disable preemption while holding the global binder lock Todd Kjos
2016-09-08 16:15 ` Todd Kjos
2016-09-08 17:46 ` Greg Kroah-Hartman
2016-09-10 16:16 ` Christoph Hellwig
2016-09-10 16:22 ` Peter Zijlstra
2016-09-10 16:37 ` Thomas Gleixner [this message]
2016-09-10 17:28 ` Greg Kroah-Hartman
2016-09-12 15:49 ` Todd Kjos
2016-09-13 3:44 ` Arve Hjønnevåg
2016-09-13 6:42 ` Greg Kroah-Hartman
2016-09-13 19:52 ` Arve Hjønnevåg
2016-09-13 7:32 ` Peter Zijlstra
2016-09-13 19:53 ` Arve Hjønnevåg
2016-09-14 7:10 ` Peter Zijlstra
2016-09-14 7:41 ` Peter Zijlstra
2016-09-14 13:38 ` Peter Zijlstra
2016-09-14 16:11 ` Peter Zijlstra
2016-09-14 16:13 ` Peter Zijlstra
2016-09-14 16:55 ` Peter Zijlstra
2016-09-17 0:42 ` Todd Kjos
2016-09-09 15:17 Todd Kjos
2016-09-09 15:44 ` Greg KH
2016-09-09 17:39 ` Todd Kjos
2016-09-10 11:18 ` Greg KH
2016-09-10 11:25 ` Greg KH
2016-09-09 16:37 ` kbuild test robot
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