Re: [PATCH RFC] x86: hpet: Avoid the readback penalty

From: Borislav Petkov
Date: Wed Sep 15 2010 - 10:39:08 EST


From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Wed, Sep 15, 2010 at 09:11:57AM -0400

> On Tue, 14 Sep 2010, tip-bot for Thomas Gleixner wrote:
> > x86: hpet: Work around hardware stupidity
>
> After my brain recovered from yesterdays exposure with the x86 timer
> horror, I came up with a different solution for this problem, which
> avoids the readback of the compare register completely. It works
> nicely on my affected ATI system, but needs some exposure to the other
> machines.

Will run in on a couple of SBx00 machines I got here.

...

> If cmp is less than 8 HPET clock cycles, then we decide that the event
> has happened already and return -ETIME. That covers the above #1 and
> #2 problems which would cause a wait for HPET wraparound (~306
> seconds).

Make sense. I guess you're choosing a value of 8 just to be on the safe
side wrt to HPET clock cycles it takes to write the cmp register?

--
Regards/Gruss,
Boris.

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