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From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <htejun@fb.com>,
	torvalds@linux-foundation.org, akpm@linux-foundation.org,
	mingo@redhat.com, axboe@kernel.dk, tytso@mit.edu, jack@suse.com,
	adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel-team@fb.com, mingbo@fb.com
Subject: Re: [PATCH 1/4] sched: move IO scheduling accounting from io_schedule_timeout() to __schedule()
Date: Mon, 31 Oct 2016 10:45:56 -0600	[thread overview]
Message-ID: <20161031164556.GC26364@mtj.duckdns.org> (raw)
In-Reply-To: <20161029032126.GH3568@worktop.programming.kicks-ass.net>

Hello,

On Sat, Oct 29, 2016 at 05:21:26AM +0200, Peter Zijlstra wrote:
> On Fri, Oct 28, 2016 at 03:12:32PM -0400, Tejun Heo wrote:
> > Hello, Peter.
> > 
> > On Fri, Oct 28, 2016 at 09:07:02PM +0200, Peter Zijlstra wrote:
> > > One alternative is to inherit the iowait state of the task we block on.
> > > That'll not get rid of the branches much, but it will remove the new
> > > mutex APIs.
> > 
> > Yeah, thought about that briefly but we don't necessarily track mutex
> 
> This one I actually fixed and should be in -next. And it would be
> sufficient to cover the use case here.

Tracking the owners of mutexes and rwsems does help quite a bit.  I
don't think it's as simple as inheriting io sleep state from the
current owner tho.  The owner might be running or in a non-IO sleep
when others try to grab the mutex.  It is an option to ignore those
cases but this would have a real possibility to lead to surprising
results in some corner cases.  If we choose to propagate dynamically,
it becomes an a lot more complex problem and I don't think it'd be
justfiable.

Unless there can be a simple enough and reliable solution, I think
it'd be better to stick with explicit marking.

Thanks.

-- 
tejun

  reply	other threads:[~2016-10-31 16:46 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-28 16:58 [PATCHSET RFC] sched, jbd2: mark sleeps on journal->j_checkpoint_mutex as iowait Tejun Heo
2016-10-28 16:58 ` [PATCH 1/4] sched: move IO scheduling accounting from io_schedule_timeout() to __schedule() Tejun Heo
2016-10-28 18:27   ` Peter Zijlstra
2016-10-28 19:07     ` Peter Zijlstra
2016-10-28 19:12       ` Tejun Heo
2016-10-29  3:21         ` Peter Zijlstra
2016-10-31 16:45           ` Tejun Heo [this message]
2016-12-06 21:30             ` Tejun Heo
2016-11-03 15:33   ` Pavan Kondeti
2016-11-08 22:51     ` Tejun Heo
2016-12-06 21:29   ` [PATCH v2 " Tejun Heo
2016-12-07  9:35     ` Peter Zijlstra
2016-12-07 20:48       ` [PATCH v3 1/4] sched: move IO scheduling accounting from io_schedule_timeout() into scheduler Tejun Heo
2017-01-14 12:49         ` [tip:sched/core] sched/core: " tip-bot for Tejun Heo
2016-10-28 16:58 ` [PATCH 2/4] sched: separate out io_schedule_prepare() and io_schedule_finish() Tejun Heo
2017-01-14 12:49   ` [tip:sched/core] sched/core: Separate " tip-bot for Tejun Heo
2016-10-28 16:58 ` [PATCH 3/4] mutex: add mutex_lock_io() Tejun Heo
2017-01-14 12:50   ` [tip:sched/core] locking/mutex, sched/wait: Add mutex_lock_io() tip-bot for Tejun Heo
2017-01-14 14:13     ` Mike Galbraith
2017-01-14 16:10       ` Ingo Molnar
2016-10-28 16:58 ` [PATCH 4/4] jbd2: use mutex_lock_io() for journal->j_checkpoint_mutex Tejun Heo
2017-01-14 12:51   ` [tip:sched/core] fs/jbd2, locking/mutex, sched/wait: Use " tip-bot for Tejun Heo

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