Date: Sat, 29 Oct 2016 05:21:26 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <htejun@fb.com>
Cc: Tejun Heo <tj@kernel.org>, 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()
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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.

> or other synchronization construct owners, things get gnarly with
> rwsems (the inode ones sometimes end up in a similar situation), and
> we'll probably end up dealing with some surprising propagations down
> the line.

rwsems could be done for writers only.