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: David Matlack <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a7f9c31..44158a4 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3275,12 +3275,23 @@ out:
 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));
        }