linux-kernel - Re: [RFC patch 0/4] TSC calibration improvements

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Date:	Thu, 4 Sep 2008 17:36:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	Alok Kataria <akataria@...are.com>,
	Arjan van de Veen <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC patch 0/4] TSC calibration improvements


* Thomas Gleixner <tglx@...utronix.de> wrote:

> This patch series addresses following:
> 
>      - reduce the calibration time to a useful value
>      - make decision smarter, when a reference (HPET/PMTIMER) is around
> 
> The first patches are cleanups to prepare for the smarter loop
> handling.
> 
> The main change is to reduce the PIT delay value to 10ms, which gives
> reasonable results on very slow machines as well. To avoid looping
> several times when the machine has a working reference counter
> (HPET/pmtimer), we compare the results of the PIT and the reference and
> break out of the loop when both match inside of a 10% window.
> 
> For virtualized environments the PIT calibration fails often and the
> reference calibration is not reproducible with 10ms. To address this
> we check whether the PIT failed two times in a row and make the PIT
> loop longer (50ms) for the last try to get a better result for the
> reference.
> 
> Most of the machines I tested break out of the loop after the first
> try with a stable reproducible result.

i've added them to tip/x86/tsc and merged it into tip/master - if 
there's test success we can merge it into x86/urgent as well and push it 
into v2.6.27. Any objections to that merge route?

	Ingo
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