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

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Message-ID: <alpine.LFD.1.10.0809041432070.3117@nehalem.linux-foundation.org>
Date:	Thu, 4 Sep 2008 14:34:55 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
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

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.

So then it returns zero, and the slow and complicated case can run.

Take a look at the generated assembly language. I literally wrote it so 
that you could imagine that it's an old-time asm hacker that wrote the 
asm. Don't screw it up.

			Linus
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