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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