linux-kernel - Re: [PATCH 1/9] sched: add schedule_timeout

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Message-ID: <20160322130822.GF10381@dhcp22.suse.cz>
Date:	Tue, 22 Mar 2016 14:08:23 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 1/9] sched: add schedule_timeout_idle()

On Tue 22-03-16 13:51:13, Peter Zijlstra wrote:
> On Tue, Mar 22, 2016 at 01:33:14PM +0100, Michal Hocko wrote:
> > On Tue 22-03-16 13:23:45, Peter Zijlstra wrote:
> > > On Tue, Mar 22, 2016 at 12:00:18PM +0100, Michal Hocko wrote:
> > > 
> > > >  extern signed long schedule_timeout_interruptible(signed long timeout);
> > > >  extern signed long schedule_timeout_killable(signed long timeout);
> > > >  extern signed long schedule_timeout_uninterruptible(signed long timeout);
> > > > +extern signed long schedule_timeout_idle(signed long timeout);
> > > 
> > > > +/*
> > > > + * Like schedule_timeout_uninterruptible(), except this task will not contribute
> > > > + * to load average.
> > > > + */
> > > > +signed long __sched schedule_timeout_idle(signed long timeout)
> > > > +{
> > > > +	__set_current_state(TASK_IDLE);
> > > > +	return schedule_timeout(timeout);
> > > > +}
> > > > +EXPORT_SYMBOL(schedule_timeout_idle);
> > > 
> > > Yes we have 3 such other wrappers, but I've gotta ask: why? They seem
> > > pretty pointless.
> > 
> > It seems it is just too easy to miss the __set_current_state (I am
> > talking from my own experience).
> 
> Well, that's what you get; if you call schedule() and forget to set a
> blocking state you also don't block, where the problem?

The error prone nature of schedule_timeout usage was the reason to
introduce them in the first place IIRC which makes me think this is
something that is not so uncommon.
 
[...]

> > > Why not kill the lot?
> > 
> > We have over 400 users, would it be much better if we open code all of
> > them? It doesn't sound like a huge win to me.
> 
> Dunno, changing them around isn't much work, we've got coccinelle for
> that.

If that sounds like a more appropriate plan I won't object. I can simply
change my patch to do __set_current_state and schedule_timeout.

-- 
Michal Hocko
SUSE Labs