On Tue, 14 Dec 2021 06:24:38 +0000, Reiji Watanabe <reijiw@xxxxxxxxxx> wrote: > > Hi Alex, > > On Mon, Dec 13, 2021 at 3:14 AM Alexandru Elisei > <alexandru.elisei@xxxxxxx> wrote: > > > > Also, as VCPUs get migrated from one physical CPU to the other, the > > semantics of the microarchitectural events change, even if the event ID is > > the same. > > Yes, I understand. As mentioned, this can work only when the > CPU affinity is set for vCPU threads appropriately (, which could > be done even without changing userspace). Implicit bindings to random PMUs based on the scheduling seems a pretty fragile API to me, and presents no real incentive for userspace to start doing the right thing. I'd prefer not counting events at all when on the wrong CPU (for some definition of 'wrong'), rather than accumulating unrelated events. Both are admittedly wrong, but between two evils, I'd rather stick with the one I know (and that doesn't require any change)... Alex's series brings a way to solve this by allowing userspace to pick a PMU and make sure userspace is aware of the consequences. It puts userspace in charge, and doesn't leave space for ambiguous behaviours. I definitely find value in this approach. M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
