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

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Message-ID: <20071208191629.GB21186@elte.hu>
Date:	Sat, 8 Dec 2007 20:16:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
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


* Arjan van de Ven <arjan@...radead.org> wrote:

> > > > 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?

doesnt the notifier still get run on the target CPU?

	Ingo
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