On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote:
> Move the halt-polling "success" and histogram stats update into the
> dedicated helper to fix a discrepancy where the success/fail "time" stats
> consider polling successful so long as the wait is avoided, but the main
> "success" and histogram stats consider polling successful if and only if
> a wake event was detected by the halt-polling loop.
>
> Move halt_attempted_poll to the helper as well so that all the stats are
> updated in a single location. While it's a bit odd to update the stat
> well after the fact, practically speaking there's no meaningful advantage
> to updating before polling.
>
> Note, there is a functional change in addition to the success vs. fail
> change. The histogram updates previously called ktime_get() instead of
> using "cur". But that change is desirable as it means all the stats are
> now updated with the same polling time, and avoids the extra ktime_get(),
> which isn't expensive but isn't free either.
>
> Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> virt/kvm/kvm_main.c | 35 ++++++++++++++++-------------------
> 1 file changed, 16 insertions(+), 19 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 4dfcd736b274..1292c7876d3f 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3204,12 +3204,23 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
> static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
> ktime_t end, bool success)
> {
> + struct kvm_vcpu_stat_generic *stats = &vcpu->stat.generic;
> u64 poll_ns = ktime_to_ns(ktime_sub(end, start));
>
> - if (success)
> - vcpu->stat.generic.halt_poll_success_ns += poll_ns;
> - else
> - vcpu->stat.generic.halt_poll_fail_ns += poll_ns;
> + ++vcpu->stat.generic.halt_attempted_poll;
> +
> + if (success) {
> + ++vcpu->stat.generic.halt_successful_poll;
> +
> + if (!vcpu_valid_wakeup(vcpu))
> + ++vcpu->stat.generic.halt_poll_invalid;
> +
> + stats->halt_poll_success_ns += poll_ns;
> + KVM_STATS_LOG_HIST_UPDATE(stats->halt_poll_success_hist, poll_ns);
> + } else {
> + stats->halt_poll_fail_ns += poll_ns;
> + KVM_STATS_LOG_HIST_UPDATE(stats->halt_poll_fail_hist, poll_ns);
> + }
> }
>
> /*
> @@ -3230,30 +3241,16 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> if (do_halt_poll) {
> ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
>
> - ++vcpu->stat.generic.halt_attempted_poll;
> do {
> /*
> * This sets KVM_REQ_UNHALT if an interrupt
> * arrives.
> */
> - if (kvm_vcpu_check_block(vcpu) < 0) {
> - ++vcpu->stat.generic.halt_successful_poll;
> - if (!vcpu_valid_wakeup(vcpu))
> - ++vcpu->stat.generic.halt_poll_invalid;
> -
> - KVM_STATS_LOG_HIST_UPDATE(
> - vcpu->stat.generic.halt_poll_success_hist,
> - ktime_to_ns(ktime_get()) -
> - ktime_to_ns(start));
> + if (kvm_vcpu_check_block(vcpu) < 0)
> goto out;
> - }
> cpu_relax();
> poll_end = cur = ktime_get();
> } while (kvm_vcpu_can_poll(cur, stop));
> -
> - KVM_STATS_LOG_HIST_UPDATE(
> - vcpu->stat.generic.halt_poll_fail_hist,
> - ktime_to_ns(ktime_get()) - ktime_to_ns(start));
> }
>
>
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Best regards,
Maxim Levitsky
