Commit 30c94347 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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KVM: Reconcile discrepancies in halt-polling stats 



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: default avatarDavid Matlack <dmatlack@google.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-8-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 29e72893

virt/kvm/kvm_main.c

+16 −19
Original line number Diff line number Diff line
@@ -3275,12 +3275,23 @@ 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);

	}

}



/*
@@ -3301,30 +3312,16 @@ 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));

	}