diff mbox series

[v2,07/43] KVM: Reconcile discrepancies in halt-polling stats

Message ID 20211009021236.4122790-8-seanjc@google.com
State New
Headers show
Series KVM: Halt-polling and x86 APICv overhaul | expand

Commit Message

Sean Christopherson Oct. 9, 2021, 2:12 a.m. UTC 
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>
---
 virt/kvm/kvm_main.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

Comments

Maxim Levitsky Oct. 27, 2021, 11:29 a.m. UTC | #1 
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@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  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@redhat.com>

Best regards,
	Maxim Levitsky
diff mbox series

Patch

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));
 	}