linux-kernel - Re: sched: fix/optimise some issues

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Message-ID: <1311210009.7746.37.camel@marge.simson.net>
Date:	Thu, 21 Jul 2011 03:00:09 +0200
From:	Mike Galbraith <efault@....de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	stephan.baerwolf@...ilmenau.de, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, ncrao@...gle.com
Subject: Re: sched: fix/optimise some issues

On Wed, 2011-07-20 at 21:11 +0200, Peter Zijlstra wrote:
> On Wed, 2011-07-20 at 15:42 +0200, Stephan Bärwolf wrote:
> > In "check_preempt_tick()" (kernel/sched_fair.c:1093) a ulong
> > called "ideal_runtime" stores a timeslice of the current task
> > (scheduling entity). This time complies real cpu-time.
> > 
> > At the end of the same function (nr_running > 1) this (real) time
> > is compared with a virtual-runtime-delta. Obviously the timeunits
> > (real vs. virtual) didn't fit.
> > 
> > Using "wakeup_preempt_entity()" instead should fix this in a even
> > more general way.

(That's what I thought at first too)

> Hrm,. I'm fairly sure we did that on purpose and the thing that is
> missing is a big fat comment. People keep trying to fix that (me
> included).
> 
> I'll try and dig up the why and such.

Better to just kill it outright.  It's not doing that much anyway.

	-Mike

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