On Thu, Jul 11, 2013 at 11:10:25AM +0300, Gleb Natapov wrote: > On Wed, Jul 10, 2013 at 10:21:57PM -0300, Marcelo Tosatti wrote: > > > > Linux as a guest on KVM hypervisor, the only user of the pvclock > > vsyscall interface, does not require notification on task migration > > because: > > > > 1. cpu ID number maps 1:1 to per-CPU pvclock time info. > > 2. per-CPU pvclock time info is updated if the > > underlying CPU changes. > > 3. that version is increased whenever underlying CPU > > changes. > > > Is this the case with KVM though? IIRC KVM does not updates kvmclock > on vcpu migration if host has synchronized TSC.
KVM does not update kvmclock on vcpu->pcpu migration if the master clock scheme is used, which depends on synchronized TSC. In that case, it is safe to migrate a thread/vcpu to another cpu without updating kvmclock area (because all vcpus contain the same value as system timestamp and different tsc_timestamps, but all (tsc_timestamps) usable as deltas on any given pcpu. So the 3 items are necessary in the general case of hypervisor maintaining distinct kvmclock vcpu areas (copy&pasted the comment from the code comment). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
