Re: [PATCH 12/14] KVM: Don't redo ktime_get() when calculating halt-polling stop/deadline
David Matlack <[email protected]>
| Newsgroups | org.kernel.vger.kvm-ppc,dev.linux.lists.kvmarm,org.infradead.lists.linux-arm-kernel,org.kernel.vger.kvm,org.kernel.vger.linux-kernel,org.kernel.vger.linux-mips |
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| Message-ID | <[email protected]> |
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 <[email protected]> Reviewed-by: David Matlack <[email protected]> > --- > 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 >