Re: [PATCH 1/1] KVM: shrink halt polling even more for invalid wakeups

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 05/17/2016 10:49 AM, Christian Borntraeger wrote:
> commit 3491caf2755e ("KVM: halt_polling: provide a way to qualify
>  wakeups during poll") added more aggressive shrinking of the
> polling interval if the wakeup did not match some criteria. This
> still allows to keep polling enabled if the polling time was
> smaller that the current max poll time (block_ns <= vcpu->halt_poll_ns).
> Performance measurement shows that even more aggressive shrinking
> (shrink polling on any invalid wakeup) reduces absolute and relative
> (to the workload) CPU usage even further.
> 
> Cc: David Matlack <dmatlack@google.com>
> Cc: Wanpeng Li <kernellwp@gmail.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Cornelia Huck <cornelia.huck@de.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
>  virt/kvm/kvm_main.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index fbd7698..dec1ed2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2055,12 +2055,13 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>  out:
>  	block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
> 
> -	if (halt_poll_ns) {
> +	if (!vcpu_valid_wakeup(vcpu))
> +		 shrink_halt_poll_ns(vcpu);
		^ hmpf. Small whitespace error. I can resend if wanted.

> +	else if (halt_poll_ns) {
>  		if (block_ns <= vcpu->halt_poll_ns)
>  			;
>  		/* we had a long block, shrink polling */
> -		else if (!vcpu_valid_wakeup(vcpu) ||
> -			(vcpu->halt_poll_ns && block_ns > halt_poll_ns))
> +		else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns)
>  			shrink_halt_poll_ns(vcpu);
>  		/* we had a short halt and our poll time is too small */
>  		else if (vcpu->halt_poll_ns < halt_poll_ns &&
>