linux-kernel - Re: [PATCH] x86: Export tsc related information in sysfs

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Message-ID: <4BF7507F.20805@zytor.com>
Date:	Fri, 21 May 2010 20:33:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	john stultz <johnstul@...ibm.com>
CC:	Brian Bloniarz <bmb@...enacr.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Venkatesh Pallipadi <venki@...gle.com>, chris.mason@...cle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Export tsc related information in sysfs

On 05/21/2010 07:03 PM, john stultz wrote:
> 
> Yea, the relative instability of the tsc calibration at boot is an
> issue for folks who want very very precise timekeeping immediately
> after a reboot.
> 
> I proposed a solution to this awhile back via a boot option users
> could use to specify the tsc_khz freq, so it would be consistent from
> boot to boot. See: https://patchwork.kernel.org/patch/22492/
> 
> It didn't really go anywhere due to a lack of public interest.
> However, if you're interested in playing with it, I can try to revive
> the patch.
> 

The point about NTP is a very good one; with NTP you *really* want what
you're adjusting to be directly related to the crystal oscillator -- as
what it is; precision over accuracy as NTP takes care of accuracy but
not precision.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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