linux-kernel - Re: [accounting regression since rc1] scheduler updates

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Message-Id: <1187687926.7623.10.camel@localhost>
Date:	Tue, 21 Aug 2007 11:18:46 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jan Glauber <jang@...ux.vnet.ibm.com>,
	heiko.carstens@...ibm.com, Paul Mackerras <paulus@...ba.org>
Subject: Re: [accounting regression since rc1]  scheduler updates

On Tue, 2007-08-21 at 09:00 +0200, Christian Borntraeger wrote:
> Am Montag, 20. August 2007 schrieb Martin Schwidefsky:
> > On Mon, 2007-08-20 at 20:08 +0200, Ingo Molnar wrote:
> > Ok, that would mean that sched_clock can just return the virtual cpu
> > time and the two hooks starts and stops the idle periods as far as the
> > scheduler is concerned. In this case we can use the patch from Jan with
> > the new implementation for sched_clock and add the two hooks to the
> > places where the cpu-idle notifiers are done (do_monitor_call and
> > default_idle). In fact this could be an idle-notifier. Hmm, I take a
> > closer look tomorrow when I'm back at the office.
> > 
> > > If a virtual CPU is idle then i think the "real = steal, virtual = 0" 
> > > way of thinking about idle looks a bit unnatural to me - wouldnt it be 
> > > better to think in terms of "steal = 0, virtual = real" ? Basically a 
> > > virtual CPU can idle at "perfect speed", without the host "stealing" any 
> > > cycles from it. And with that way of thinking, if s390 passed in the 
> > > real-idle-time value to the new callbacks below it would all fall into 
> > > place. Hm?
> 
> Martin,
> 
> I think we already do something like this. If you look at cpustat in 2.6.22 
> and earlier we already have steal increase = 0, idle increase = 100 % on an 
> idle cpu, even on s390. So while from the hardware perspective steal is 
> growing, we do the right thing in Linux, no?

This is done in kernel/sched.c:account_steal_time(). If the architecture
backend reports steal time for idle it is accounted as idle time.

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.


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