| Date | Mon, 25 Oct 2021 16:26:08 +0200 | Subject | Re: [PATCH v2 16/43] KVM: Don't redo ktime_get() when calculating halt-polling stop/deadline | From | Paolo Bonzini <> |
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On 09/10/21 04:12, 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.
Using "start" makes the change even more obvious, so:
Calculate the halt-polling "stop" time using "start" instead of redoing ktime_get(). In practice, the numbers involved are in the noise (e.g., in the happy case where hardware correctly predicts do_halt_poll and there are no interrupts, "start" is probably only a few cycles old) and either approach is perfectly ok. But it's more precise to count any extra latency toward the halt-polling time.
Paolo
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