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

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Message-ID: <20071208121811.4e202804@laptopd505.fenrus.org>
Date:	Sat, 8 Dec 2007 12:18:11 -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 Sat, 8 Dec 2007 20:16:29 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * 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?
> 

.... if and only if the BIOS actually gives correct information to the
OS.

In reality... that's not a very common thing on this field sadly

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