On Fri, 04 Nov 2022 06:20:59 +0000, Usama Arif <usama.arif@xxxxxxxxxxxxx> wrote: > > This patchset adds support for vcpu_is_preempted in arm64, which > allows the guest to check if a vcpu was scheduled out, which is > useful to know incase it was holding a lock. vcpu_is_preempted can > be used to improve performance in locking (see owner_on_cpu usage in > mutex_spin_on_owner, mutex_can_spin_on_owner, rtmutex_spin_on_owner > and osq_lock) and scheduling (see available_idle_cpu which is used > in several places in kernel/sched/fair.c for e.g. in wake_affine to > determine which CPU can run soonest): [...] > pvcy shows a smaller overall improvement (50%) compared to > vcpu_is_preempted (277%). Host side flamegraph analysis shows that > ~60% of the host time when using pvcy is spent in kvm_handle_wfx, > compared with ~1.5% when using vcpu_is_preempted, hence > vcpu_is_preempted shows a larger improvement. And have you worked out *why* we spend so much time handling WFE? M. -- Without deviation from the norm, progress is not possible.
