On Thu, Mar 14, 2024, Paolo Bonzini wrote: > On Fri, Mar 8, 2024 at 11:37 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > > - Zap TDP MMU roots at 4KiB granularity to minimize the delay in yielding if > > a reschedule is needed, e.g. if a high priority task needs to run. Because > > KVM doesn't support yielding in the middle of processing a zapped non-leaf > > SPTE, zapping at 1GiB granularity can result in multi-millisecond lag when > > attempting to schedule in a high priority. > > > > Would 2 MiB provide a nice middle ground? Not really? Zapping at 2MiB definitely fixes the worst of the tail latencies, but there is still a measurable difference between 2MiB and 4KiB. And on the other side of the coing, I was unable to observe a meaningful difference in total runtime by zapping at 2MiB, or even 1GiB, versus 4KiB. In other words, AFAICT, there's no need to shoot for a middle ground because trying to zap at larger granularities doesn't buy us anything.
