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Subject: Re: + stupid-hack-to-make-mainline-build.patch added to -mm tree
From: Thomas Gleixner <tglx@linutronix.de>
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To: Dan Hecht <dhecht@vmware.com>
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Date: Wed, 07 Mar 2007 01:49:04 +0100
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On Tue, 2007-03-06 at 16:35 -0800, Dan Hecht wrote:
> >> There is no problem for realtime uses, as the reprogramming path is
> >> running with local interrupts disabled. I can see the point for paravirt
> >> and I'm not opposed to change / expand the interface for that. It might
> >> be done by an extra clockevents feature flag, which requests absolute
> >> time instead of relative time.
> >>   
> > 
> > I'm not sure how much different it makes overall.  It's true that
> > absolute time would be a more useful interface, but because the guest
> > vcpu can be preempted at any time, we could miss the timeout
> > regardless.  In Xen if you set a timeout for the past you get an
> > immediate interrupt; I presume the clockevent code can deal with that?
> > 
> 
> That's the problem though, you won't know to set it for the past since 
> the expiry is relative.  When the vcpu starts running again, it will set 
> the timer to expire X ns from now, not Xns from when the timer was 
> requested.

Ooops. I completely forgot, that you get the absolute expiry time
already in ktime_t format (nanoseconds) when dev->set_next_event() is
called.

	dev->next_event = expires;

is done right before the call. 

So it's already there for free.

	tglx