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

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Message-ID: <48C02957.40708@zytor.com>
Date:	Thu, 04 Sep 2008 11:30:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Alok Kataria <akataria@...are.com>,
	Arjan van de Veen <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC patch 0/4] TSC calibration improvements

Linus Torvalds wrote:
> 
> Of course, the 2048 PIT ticks is just a random choice. It could be any 
> multiple of 256 ticks, so that error can be made smaller. Maybe it's worth 
> spending 10ms on this, and get it down by a factor of five (at which point 
> the error on the PIT frequency is probably in the same order of 
> magnitude).
> 

FWIW, typical error on the 14.31818 MHz clock (used as the PIT, PMTMR 
and HPET timebase in most systems) is usually ±50 ppm.  High-quality 
motherboards which use a TCXO for the 14.31818 MHz clock would have
around ±1 ppm.

	-hpa
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