Re: [RFC][PATCH 3/7] sched: Allow balance callbacks for check_class_changed()

From: Peter Zijlstra <peterz@infradead.org>
To: Kirill Tkhai <tkhai@yandex.ru>
Cc: "umgwanakikbuti@gmail.com" <umgwanakikbuti@gmail.com>,
	"mingo@elte.hu" <mingo@elte.hu>,
	"ktkhai@parallels.com" <ktkhai@parallels.com>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"juri.lelli@gmail.com" <juri.lelli@gmail.com>,
	"pang.xunlei@linaro.org" <pang.xunlei@linaro.org>,
	"oleg@redhat.com" <oleg@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"luca.abeni@unitn.it" <luca.abeni@unitn.it>
Subject: Re: [RFC][PATCH 3/7] sched: Allow balance callbacks for check_class_changed()
Date: Wed, 3 Jun 2015 09:32:27 +0200	[thread overview]
Message-ID: <20150603073227.GW3644@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <249151433262439@web6m.yandex.ru>

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.