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Re: [Xen-devel] [PATCH 2/4] CPUIDLE: Avoid remnant LAPIC timer intr whil

To: "Wei, Gang" <gang.wei@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/4] CPUIDLE: Avoid remnant LAPIC timer intr while force hpetbroadcast
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 11 Sep 2008 11:38:19 +0100
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On 10/9/08 15:25, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:

>> It's not clear to me the disable/enable_LAPIC_timer() work is worthwhile for
>> the few timer interrupts it is likely to avoid. The other bit of the patch
>> is a good bugfix though. I've taken just the latter part.
> Thanks for accept most of these patches. As to disable/enable_LAPIC_timer(), I
> add them because some platforms require the LAPIC timer intr being disabled
> before entering C3, otherwise there may be some unexpected things. As a
> reference, Linux kernel always do so.

Can you point out where Linux does so? It's not obvious to me.

Also, in your patch, you unmask LVTT after reprogramming the LAPIC counter.
Isn't there a race where the LAPIC timer generates an interrupt event before
you unmask the LVTT and hence you lose the interrupt (since I assume the
LAPIC interrupt is basically an internal one-shot signal which does not get
latched in any way)? So you'd probably need to reprogram_timer(0), then
enable the timer, then reprogram_timer(<actual value>).

 -- Keir

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