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Date: Wed, 15 Sep 2010 16:40:34 +0200
From: Borislav Petkov <borislav.petkov@amd.com>
To: Thomas Gleixner <tglx@linutronix.de>
CC: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
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        Damien Wyart <damien.wyart@free.fr>,
        John Drescher <drescherjm@gmail.com>,
        Venkatesh Pallipadi <venki@google.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        "Herrmann3, Andreas" <Andreas.Herrmann3@amd.com>,
        Suresh Siddha <suresh.b.siddha@intel.com>
Subject: Re: [PATCH RFC] x86: hpet: Avoid the readback penalty
Message-ID: <20100915144034.GC968@aftab>
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From: Thomas Gleixner <tglx@linutronix.de>
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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