On Thu, 2024-08-01 at 22:00 +0200, Thomas Gleixner wrote: > On Thu, Aug 01 2024 at 20:21, David Woodhouse wrote: > > On Thu, 2024-08-01 at 21:06 +0200, Thomas Gleixner wrote: > > > Yes. So the sequence should stop KVM from trying to inject > > > interrupts. Maybe someone fixes it to actually stop fiddling with the > > > counter too :) > > > > I don't think we care about the counter value, as that's *calculated* > > on demand when the guest tries to read from it. Or, more to the point, > > *if* the guest tries to read from it. > > > > As opposed to the interrupt, which is a timer in the VMM which takes a > > CPU out of guest mode and incurs steal time, just to waggle a pin on > > the emulated PICs for no good reason. > > Well, if the implementation still arms the timer in the background, then > it matters because that has to be processed too. I haven't looked at > that code at all, so what do I know. It only needs to arm the timer if it needs to send an interrupt. Otherwise, it's all event-driven from the guest interaction. > > > > I'm glad I decided to export a function from the clocksource driver and > > > > just *call* it from pit_timer_init() though. Means we can bikeshed the > > > > shutdown sequence in *one* place and it isn't duplicated. > > > > > > Right. Though we don't have to make this conditional on hypervisor I > > > think. > > > > Right, we don't *have* to. I vacillated about that and almost ripped it > > out before sending the patch, but came down on the side of "hardware is > > a steaming pile of crap and if I don't *have* to change its behaviour, > > let's not touch it". > > > > I justify my cowardice on the basis that it doesn't *matter* if a > > hardware implementation is still toggling the IRQ pin; in that case > > it's only a few irrelevant transistors which are busy, and it doesn't > > translate to steal time. > > On real hardware it translates to power... Perhaps, although I'd guess it's a negligible amount. Still, happy to be brave and make it unconditional. Want a new version of the patch?
Attachment:
smime.p7s
Description: S/MIME cryptographic signature
