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Subject: Re: sched: fix/optimise some issues
From: Peter Zijlstra <peterz@infradead.org>
To: stephan.baerwolf@tu-ilmenau.de
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        ncrao@google.com, Mike Galbraith <efault@gmx.de>
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Date: Wed, 20 Jul 2011 21:11:30 +0200
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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. 

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.