On Fri, 2010-02-26 at 13:51 +0200, Avi Kivity wrote: > It would be the other way round - the host would steal the pmu from the > guest. Later we can try to time-slice and extrapolate, though that's > not going to be easy. Right, so perf already does the time slicing and interpolating thing, so a soft-pmu gets that for free. Anyway, this discussion seems somewhat in a stale-mate position. The KVM folks basically demand a full PMU MSR shadow with PMI passthrough so that their $legacy shit works without modification. My question with that is how $legacy muck can ever know how the current PMU works, you can't even properly emulate a core2 pmu on a nehalem because intel keeps messing with the event codes for every new model. So basically for this to work means the guest can't run legacy stuff anyway, but needs to run very up-to-date software, so we might as well create a soft-pmu/paravirt interface now and have all up-to-date software support that for the next generation. Furthermore, when KVM doesn't virtualize the physical system topology, some PMU features cannot even be sanely used from a vcpu. So while currently a root user can already tie up all of the pmu using perf, simply using that to hand the full pmu off to the guest still leaves lots of issues. -- 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
