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

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Date:	Thu, 4 Sep 2008 23:39:45 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Alok Kataria <akataria@...are.com>,
	Arjan van de Veen <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC patch 0/4] TSC calibration improvements


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, 4 Sep 2008, Linus Torvalds wrote:
> > 
> > Face it, if somebody tries to make QUICK_PIT_MS be so large as to 
> > that be an issue, then the whole point of the function goes away.
> 
> Btw, the same is true of adding any random "sanity checking". The 
> point of that thing was to simply only work when the PIT works as 
> advertized, and fail immediately if it doesn't. Even *if* you were to 
> pick a big calibration delay *and* if you happened to have a PIT that 
> is broken and doesn't wrap correctly, the design of the thing would 
> mean that it would then fail the calibration already.
> 
> Exactly because it would _see_ that it's not wrapping.

yeah - pit_expect_msb() would return after 50,000 iterations with a 
failure. So i was wondering whether for such PITs we _want_ the slow and 
complicated case to run.

Probably not, because the PIT could quite likely still be counting very 
precisely as long as no wraparound was involved.

	Ingo
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