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Re: [Xen-devel] Re: [PATCH] xen: always handle VIRQ_TIMER first.

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] xen: always handle VIRQ_TIMER first.
From: Keir Fraser <keir@xxxxxxx>
Date: Sun, 17 Oct 2010 08:38:35 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Campbell <ian.campbell@xxxxxxxxxx>
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Thread-topic: [Xen-devel] Re: [PATCH] xen: always handle VIRQ_TIMER first.
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On 17/10/2010 07:11, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

>> We fixed it the way we did in 'classic Xen' patched kernels since it seemed
>> arhitecturally neatest. I can accept that in the tickless kernel world that
>> may not actually be true.
> 
> I think (but I haven't spelunked into that code lately) that after a
> tickless idle period it will update jiffies N ticks based on the
> clocksource, and then run any other interrupt handler code, so jiffies
> will always appear to be up to date.

Okay, that should suffice. That presumably calls into the clocksource and
gives us our opportunity to sync with Xen's current system time. Effectively
it's just hooking into the interrupt handling preamble at a different, more
generic, point. :-)

 -- Keir



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