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Date: Fri, 3 May 2013 11:43:23 +0100
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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To: Christopher Covington <cov@codeaurora.org>
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Subject: Re: [Xen-devel] [PATCH 1/3] arm_arch_timer: introduce
 arch_timer_stolen_ticks
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On Thu, 2 May 2013, Christopher Covington wrote:
> > So the virtual timer should appear to have been running even while time
> > is being stolen and therefore stolen time needs to be accounted via some
> > other means.
> 
> Something that's not currently obvious to me is that given that the stolen
> cycle accounting should be done, what makes the architected timer interrupt
> handler the ideal place to do it?

That is a good question and I would appreciate suggestions to improve
the patch.

Given that Xen x86 and ia64 does stolen time accounting from the timer
interrupt handler:

arch/x86/xen/time.c:xen_timer_interrupt
arch/ia64/kernel/time.c:timer_interrupt

and given that the arch_timer is the only timer used by Xen on ARM and
that it includes a virt_timer that is made on purpose to be used by
virtual machines, I thought that it might be a good place for it.

I also thought that doing it this way, KVM should be able to reuse the
same hook.