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

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] xen: always handle VIRQ_TIMER first.
From: Keir Fraser <keir@xxxxxxx>
Date: Sat, 16 Oct 2010 08:14:07 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Campbell <ian.campbell@xxxxxxxxxx>
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Thread-topic: [PATCH] xen: always handle VIRQ_TIMER first.
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On 15/10/2010 22:11, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

>> When guest resumes execution after a long period blocked, the unblocking
>> interrupt may be handled before the inevitable timer interrupt which
> Why "inevitable"?  What if the next timer event is still some time in
> the future?  Or are you assuming the timer is driven by the default Xen
> 100Hz timer?

Do you sometimes disable, or indeed never use, VCPUOP_set_periodic_timer?

Hmmm... Perhaps as you suggest this would be a generic issue with any
tickless kernel, and the correct upstream fix for issues such as USB kbd
repeat -- if indeed such issues still exist -- is to fix such hardirq
handlers to not depend on jiffies.

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.

 -- Keir

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