linux-kernel - Re: [PATCH] Greatly improve TSC calibration using a delayed workqueue

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Message-ID: <20101110134700.GB7205@basil.fritz.box>
Date:	Wed, 10 Nov 2010 14:47:01 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Clark Williams <williams@...hat.com>
Subject: Re: [PATCH] Greatly improve TSC calibration using a delayed
 workqueue

On Tue, Nov 09, 2010 at 01:41:40PM -0800, john stultz wrote:
> > It may happen with opportunistic suspend if the system boots very fast.
> 
> Right, but a system using opportunistic suspend will have a hard enough
> time keeping close NTP sync on its own given the frequent switching
> between the fine-grained ntp adjusted clocksource during run-time and
> the coarse non-adjusted RTC/persisitent_clock while suspended.
> 
> So I think such a system would be fine it falls back to using just the
> boot-calibration for TSC freq rather then the refined calibration freq
> calculated by this patch (which will happen automatically if the refined
> calibration is off by 1%).
> 
> Does that seem like a reasonable tradeoff?

Yes it sounds good to me.  Some inaccuracy in this case is fine I guess.
Just major inaccuracy or a crash or hang wouldn't be good.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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