linux-kernel - Re: Fwd: [GIT PULL] timer changes for v3.10

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Date:	Tue, 7 May 2013 08:53:48 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Feng Tang <feng.tang@...el.com>
Cc:	Pavel Machek <pavel@....cz>, John Stultz <john.stultz@...aro.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Fwd: [GIT PULL] timer changes for v3.10


* Feng Tang <feng.tang@...el.com> wrote:

> > is even worse than that. Machine can stay is s2ram for weeks (for a 
> > lot more if it is desktop and you do s2ram for powersaving). Also 
> > temperature of CPU varies a lot between active and s2ram states. Is 
> > TSC good enough?
> 
> Yes, I think it is relatively precise. Per our test, system time backed 
> by the S3 non stop TSC only has 1 second drift after 4 days running 
> (with mixed running and S3 states). And before using this feature, we've 
> seen many time drift problems due to the RTC HW or system FW with our 
> platforms.

Nice result ...

Is that with NTP running?

Without NTP, the TSC fast-calibration on bootup is not (expected to be) 
nearly as precise as the 1:345600 precision you've measured.

Thanks,

	Ingo
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