Re: kvm & dyntick

[Ingo Molnar <mingo@elte.hu>]

* Avi Kivity <avi@qumranet.com> wrote:

> >( for this to work on my system i have added a 'hyper' clocksource
> >  hypercall API for KVM guests to use - this is needed instead of the 
> >  running-to-slowly TSC. )
> >  
> 
> What's the problem with the TSC?  The only issue I'm aware of is that 
> the tsc might go backwards if the vcpu is migrated to another host cpu 
> (easily fixed).

this is not a problem of KVM - this is a problem of this laptop: its TSC 
stops when going idle. So the TSC is fundamentally unusable for reliable 
timekeeping - and qemu doesnt offer pmtimer emulation to fall back to, 
so the dyntick kernel refused to go high-res under KVM. Once i added the 
hyper clocksource to fall back to, it could utilize the PIT and the 
lapic for clock-events.

	Ingo