linux-kernel - Re: [RFC][PATCH 3/7] sched: Allow balance callbacks for check_class

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Date:	Wed, 3 Jun 2015 09:32:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	"umgwanakikbuti@...il.com" <umgwanakikbuti@...il.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ktkhai@...allels.com" <ktkhai@...allels.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"juri.lelli@...il.com" <juri.lelli@...il.com>,
	"pang.xunlei@...aro.org" <pang.xunlei@...aro.org>,
	"oleg@...hat.com" <oleg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"luca.abeni@...tn.it" <luca.abeni@...tn.it>
Subject: Re: [RFC][PATCH 3/7] sched: Allow balance callbacks for
 check_class_changed()

On Tue, Jun 02, 2015 at 07:27:19PM +0300, Kirill Tkhai wrote:
> > +	 * task_dead_dl() will cancel our timer if we happen to die while
> > +	 * its still pending.
> 
> task_dead_dl() is called for tasks of deadline class only. So if we do that,
> the timer may be executed after final task's dead.

Indeed; sleep deprived brain misses the obvious :/

I can't seem to come up with anything much better than pulling that
hrtimer_cancel() into finish_task_switch(), however sad that is.

Something like:

  for_each_class(class) {
	if (class->task_dead)
		class->task_dead(prev);
  }

Would be nicest, but will slow down the common case. And a callback list
has the downside of having to preallocate entries for every task,
causing mostly pointless memory overhead.


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