On Jul 5, 2016 1:36 PM, "Paolo Bonzini" <pbonzini@xxxxxxxxxx> wrote: > > Bad things happen if a guest using the TSC deadline timer is migrated. > The guest doesn't re-calibrate the TSC after migration, and the > TSC frequency can and will change unless your processor supports TSC > scaling (on Intel this is only Skylake) or your data center is perfectly > homogeneous. > > The solution in this patch is to skip tsc_khz, and instead derive the > frequency from kvmclock's (mult, shift) pair. Because kvmclock > parameters convert from tsc to nanoseconds, this needs a division > but that's the least of our problems when the TSC_DEADLINE_MSR write > costs 2000 clock cycles. Luckily tsc_khz is really used by very little > outside the tsc clocksource (which kvmclock replaces) and the TSC > deadline timer. I'm wondering if it would be more straightforward to blacklist the APIC timer entirely (on KVM guests that have the TSC deadline capability) and to instead offer a paravirt clockevent that still uses the deadline timer under the hood. After all, these systems should be mostly quirk-free, so I imagine that the whole implementation would only be a few lines of code. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
