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

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Message-ID: <20160322125113.GO6344@twins.programming.kicks-ass.net>
Date:	Tue, 22 Mar 2016 13:51:13 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michal Hocko <mhocko@...nel.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, 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?

> This also seems to be a pretty common
> pattern so why not wrap it under a common call.

It just seems extremely silly to create a (out-of-line even) function
for a store and a call.

> > 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.