On Fri, Sep 24, 2021 at 05:55:26PM -0700, Sean Christopherson wrote:
> Calculate the halt-polling "stop" time using "cur" instead of redoing
> ktime_get(). In the happy case where hardware correctly predicts
> do_halt_poll, "cur" is only a few cycles old. And if the branch is
> mispredicted, arguably that extra latency should count toward the
> halt-polling time.
>
> In all likelihood, the numbers involved are in the noise and either
> approach is perfectly ok.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>
> ---
> virt/kvm/kvm_main.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2980d2b88559..80f78daa6b8d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3267,7 +3267,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu)
>
> start = cur = poll_end = ktime_get();
> if (do_halt_poll) {
> - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
> + ktime_t stop = ktime_add_ns(cur, vcpu->halt_poll_ns);
>
> do {
> /*
> --
> 2.33.0.685.g46640cef36-goog
>
