Re: + stupid-hack-to-make-mainline-build.patch added to -mm tree

Thomas Gleixner
2007-03-07T00:43:00Z

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