linux-kernel - Re: [patch] x86: scale cyc_2_nsec according to CPU frequency

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Message-ID: <20071208075735.4700bcac@laptopd505.fenrus.org>
Date:	Sat, 8 Dec 2007 07:57:35 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Guillaume Chazarain <guichaz@...oo.fr>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stefano Brivio <stefano.brivio@...imi.it>,
	Robert Love <rml@...h9.net>, linux-kernel@...r.kernel.org,
	Dave Jones <davej@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Michael Buesch <mb@...sch.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch] x86: scale cyc_2_nsec according to CPU frequency

On Fri, 7 Dec 2007 15:52:06 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Guillaume Chazarain <guichaz@...oo.fr> wrote:
> 
> > Le Fri, 7 Dec 2007 14:55:25 +0100,
> > Ingo Molnar <mingo@...e.hu> a ??crit :
> > 
> > > Firstly, we dont need the 'offset' anymore because cpu_clock() 
> > > maintains offsets itself.
> > 
> > Yes, but a lower quality one. __update_rq_clock tries to compensate 
> > large jumping clocks with a jiffy resolution, while my offset
> > arranges for a very smooth frequency transition.
> 
> yes, but that would be easy to fix up via calling 
> sched_clock_idle_wakeup_event(0) when doing a frequency transition, 
> without burdening the normal sched_clock() codepath with the offset.
> See the attached latest version.


can this deal with dual/quad core where the frequency of one core
changes if the sofware changes the frequency of the other core?


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