linux-kernel - Re: [Patch] Fix the possibility of insane return value of hpet

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Date:	Mon, 16 Mar 2009 09:59:09 +0100
From:	Vojtech Pavlik <vojtech@...e.cz>
To:	Yasunori Goto <y-goto@...fujitsu.com>
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>, clemens@...isch.de,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	robert.picco@...com, venkatesh.pallipadi@...el.com,
	mingo@...hat.com
Subject: Re: [Patch] Fix the possibility of insane return value of
	hpet_calibrate() against SMI.

On Mon, Mar 16, 2009 at 11:34:55AM +0900, Yasunori Goto wrote:

> > I've no sense of feel for how long each calibration run would take.
> > Would doing it 5 times show up as a significant increase in the boot
> > time for those that care about boot time being as quick as possible?
> 
> Hmm. The loop times is trade off against reliable value....
> Though SMI is rare interruption, I don't know how frequent
> hypervisor's switch is.
> 
> Each calibration of this has 1 milli second.
> Do you think 5 msec is too long?
> If yes, how is 3 msec? Is it still too long?

I would suggest to instead repeat until the total cycle count stops
decreasing: That way we can avoid a SMI and yet in the best case only
run the calibration 2 times.

-- 
Vojtech Pavlik
Director SuSE Labs
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