Messages in this thread | | | Date | Wed, 15 Sep 2010 16:42:38 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH RFC] x86: hpet: Avoid the readback penalty |
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On Wed, 15 Sep 2010, Borislav Petkov wrote:
> 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?
Yes, I do _NOT_ trust those hardware dudes at all. A factor 4 seems to be an appropriate choice:)
Thanks,
tglx
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