Re: [patch 1/2] KVM: hlt emulation should take in-kernel APIC/PIT timers into account

Marcelo Tosatti
2008-05-09T14:53:00Z

On Fri, May 09, 2008 at 03:49:20PM +0800, Yang, Sheng wrote:
> On Sunday 13 April 2008 17:28:22 Avi Kivity wrote:
> > Marcelo Tosatti wrote:
> > > On Fri, Apr 11, 2008 at 03:12:41PM +0300, Avi Kivity wrote:
> > >> This breaks ia64 (and shouldn't s390 use this too?)
> > >>
> > >>> * We will block until either an interrupt or a signal wakes us up
> > >>> */
> > >>> while (!kvm_cpu_has_interrupt(vcpu)
> > >>> + && !kvm_cpu_has_pending_timer(vcpu)
> > >>
> > >> I guess the fix is to stub this out for the other archs.
> > >
> > > Agreed. How's this.
> >
> > Better :); applied.
>
> Hi, Marcelo
>
> This patch got into trouble when OS don't use PIT/LAPIC timer and don't
> disable them. Then the pending counters would keep increasing, but the HLT
> emulation can't be executed. And this would resulted in mass a lot (above
> 220,000 per second) halt_exit for the Windows XP that using RTC as the
> clocksource (and keep PIT enabled after bios did, just mask the pin) idle,
> and the cpu utilize would be about 100% of QEmu process.
>
> The following patch used another way to fix the issue, though not very formal.

Hi Sheng,

Did you have kvm.git commit 8ae6dc90ac84d9734e343210c8ec709f50cd9d89
when testing this?

I believe it should fix that issue, because "ps->inject_pending" won't
be set by kvm_pit_timer_intr_post() if the IRQ is masked. Please correct
me if I'm wrong.