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

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Date:	Tue, 17 Mar 2009 19:12:16 +0900
From:	Yasunori Goto <y-goto@...fujitsu.com>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	robert.picco@...com, venkatesh.pallipadi@...el.com,
	vojtech@...e.cz, mingo@...hat.com
Subject: Re: [Patch] Fix the possibility of insane return value of hpet_calibrate() against SMI.


Sorry for late response.

> 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.
> 
> Could you, just for testing, run the calibration five thousand times or
> so instead of five times, and count how often you get insane values?
> (And how much delay does such an SMI add?)

I tried 50000 times. But insane value was nothing.
I think SMI is very rare.

> > Each calibration of this has 1 milli second.
> > Do you think 5 msec is too long?
> 
> This shouldn't matter when booting.  Anyway, I think it's possible to
> increase TICK_CALIBRATE without losing too much accuracy.

Hmm. If the person who is trying to reduce boot time for fastboot dislikes this impact,
then I'll try Vojtech-san's way.


Thanks.
-- 
Yasunori Goto 


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