linux-kernel - Re: delayacct regression in 2.6.24 git

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Message-ID: <20071103083109.GD10760@elte.hu>
Date:	Sat, 3 Nov 2007 09:31:09 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: delayacct regression in 2.6.24 git


* Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> >> Am I missing something?
> > 
> > delay accounting was causing context-switch slowdown because it 
> > called sched_clock() explicitly - but indeed my fix to that is wrong 
> > ...
> > 
> > how about reverting the change but also using rq->clock instead of 
> > sched_clock()?
> 
> Hmm... I think that might work, I find that schedule() calls 
> __update_rq_clock() which in turn calls sched_clock(), so it might be 
> a worthwhile optimization.

yep, that's the idea - in general rq->clock is updated for almost every 
scheduling event so you can rely on it instead of calling sched_clock() 
directly.

	Ingo
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