Subject: Re: [PATCH 02/14] KVM: Update halt-polling stats if and only if halt-polling was attempted

From: David Matlack <[email-masked]>
Date: Tue, 28 Sep 2021 18:57:46 +0000

On Fri, Sep 24, 2021 at 05:55:16PM -0700, Sean Christopherson wrote:
> Don't update halt-polling stats if halt-polling wasn't attempted.  This
> is a nop as @poll_ns is guaranteed to be '0' (poll_end == start), but it
> will allow a future patch to move the histogram stats into the helper to
> resolve a discrepancy in what is considered a "successful" halt-poll.
> 
> No functional change intended.
> 
> Cc: David Matlack <[email-masked]>
> Signed-off-by: Sean Christopherson <[email-masked]>

Reviewed-by: David Matlack <[email-masked]>

> ---
>  virt/kvm/kvm_main.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 768a4cbb26a6..8b33f5045b4d 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3214,6 +3214,7 @@ update_halt_poll_stats(struct kvm_vcpu *vcpu, u64 poll_ns, bool waited)
>  void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>  {
>  	bool halt_poll_allowed = !kvm_arch_no_poll(vcpu);
> +	bool do_halt_poll = halt_poll_allowed && vcpu->halt_poll_ns;
>  	ktime_t start, cur, poll_end;
>  	bool waited = false;
>  	u64 block_ns;
> @@ -3221,7 +3222,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>  	kvm_arch_vcpu_blocking(vcpu);
>  
>  	start = cur = poll_end = ktime_get();
> -	if (vcpu->halt_poll_ns && halt_poll_allowed) {
> +	if (do_halt_poll) {
>  		ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
>  
>  		++vcpu->stat.generic.halt_attempted_poll;
> @@ -3273,8 +3274,9 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>  	kvm_arch_vcpu_unblocking(vcpu);
>  	block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
>  
> -	update_halt_poll_stats(
> -		vcpu, ktime_to_ns(ktime_sub(poll_end, start)), waited);
> +	if (do_halt_poll)
> +		update_halt_poll_stats(
> +			vcpu, ktime_to_ns(ktime_sub(poll_end, start)), waited);
>  
>  	if (halt_poll_allowed) {
>  		if (!vcpu_valid_wakeup(vcpu)) {
> -- 
> 2.33.0.685.g46640cef36-goog
> 

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