Re: [PATCH 1/1] KVM: halt_polling: provide a way to qualify wakeups during poll

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Wed, 4 May 2016 09:50:57 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> The feedback about the logic triggered some more experiments on my side.
> So I was experimenting with some different workloads/heuristics and it
> seems that even more aggressive shrinking (basically resetting to 0 as soon
> as an invalid poll comes along) does improve the cpu usage even more.

Do we still keep the shrink instead of resetting to 0 explicitly? (In
case the default shrink factor was set to != 0.) We'd lose a tuneable,
but it seems the aggressiveness is warranted.

> (So the new diff looks like)
> @@ -2034,7 +2036,9 @@ 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);
> +       else if (halt_poll_ns) {
>                 if (block_ns <= vcpu->halt_poll_ns)
>                         ;

...making this

if (halt_poll_ns && vcpu_valid_wakeup(vcpu)) {