On Tue, 2007-03-06 at 16:24 -0800, Jeremy Fitzhardinge wrote: > >> 3) clockevent set_next_event interface is suboptimal for paravirt (and > >> probably realtime-ish uses). The problem is that the expiry is passed > >> as a relative time. On paravirt, an arbitrary amount of (stolen) time > >> may have passed since the delta was computed and when the timer device > >> is programmed, causing that next interrupt to be too far out in the > >> future. It seems a better interface for set_next_event would be to pass > >> the current time and the absolute expiry. Actually, I sent email to > >> Thomas and Ingo about this (and some other clockevents/hrtimer feedback) > >> in July 2006, but never heard back. Thoughts? > >> > > > > 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? Yep. You also can return -ETIME so it just works w/o an interrupt. tglx _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxx https://lists.osdl.org/mailman/listinfo/virtualization
