linux-kernel - Re: [PATCH 1/4] sched: move IO scheduling accounting from io_schedule_timeout() to _

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Message-ID: <20161029032126.GH3568@worktop.programming.kicks-ass.net>
Date:   Sat, 29 Oct 2016 05:21:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <htejun@...com>
Cc:     Tejun Heo <tj@...nel.org>, torvalds@...ux-foundation.org,
        akpm@...ux-foundation.org, mingo@...hat.com, axboe@...nel.dk,
        tytso@....edu, jack@...e.com, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, mingbo@...com
Subject: Re: [PATCH 1/4] sched: move IO scheduling accounting from
 io_schedule_timeout() to __schedule()

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.