Hi Sean, On Thu, 18 Apr 2019 at 01:18, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > KVM's recently introduced adaptive tuning of lapic_timer_advance_ns has > several critical flaws: [.../...] > > - TSC scaling is done on a per-vCPU basis, while the advancement value > is global. This issue is also present without adaptive tuning, but > is now more pronounced. Did you test this against overcommit scenario? Your per-vCPU variable can be a large number(yeah, below your 5000ns) when neighbour VMs on the same host consume cpu heavily, however, kvm will wast a lot of time to wait when the neighbour VMs are idle. My original patch evaluate the conservative hypervisor overhead when the first VM is deployed on the host. It doesn't matter whether or not the VMs on this host alter their workload behaviors later. Unless you tune the per-vCPU variable always, however, I think it will introduce more overhead. So Liran's patch "Consider LAPIC TSC-Deadline Timer expired if deadline too short" also can't depend on this. Regards, Wanpeng Li
