Re: [PATCH v2 13/35] KVM: x86: hyper-v: optimize and cleanup kvm_hv_process_stimers()

Vitaly Kuznetsov
2023-12-04T09:53:19Z

Yury Norov <yury.norov@gmail.com> writes:

> The function traverses stimer_pending_bitmap in a for-loop bit by bit.
> We can do it faster by using atomic find_and_set_bit().
>
> While here, refactor the logic by decreasing indentation level.
>
> CC: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> ---
> arch/x86/kvm/hyperv.c | 39 +++++++++++++++++++--------------------
> 1 file changed, 19 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 238afd7335e4..a0e45d20d451 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -870,27 +870,26 @@ void kvm_hv_process_stimers(struct kvm_vcpu *vcpu)
> if (!hv_vcpu)
> return;
>
> - for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
> - if (test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap)) {
> - stimer = &hv_vcpu->stimer[i];
> - if (stimer->config.enable) {
> - exp_time = stimer->exp_time;
> -
> - if (exp_time) {
> - time_now =
> - get_time_ref_counter(vcpu->kvm);
> - if (time_now >= exp_time)
> - stimer_expiration(stimer);
> - }
> -
> - if ((stimer->config.enable) &&
> - stimer->count) {
> - if (!stimer->msg_pending)
> - stimer_start(stimer);
> - } else
> - stimer_cleanup(stimer);
> - }
> + for_each_test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap,
> + ARRAY_SIZE(hv_vcpu->stimer)) {
> + stimer = &hv_vcpu->stimer[i];
> + if (!stimer->config.enable)
> + continue;
> +
> + exp_time = stimer->exp_time;
> +
> + if (exp_time) {
> + time_now = get_time_ref_counter(vcpu->kvm);
> + if (time_now >= exp_time)
> + stimer_expiration(stimer);
> }
> +
> + if (stimer->config.enable && stimer->count) {
> + if (!stimer->msg_pending)
> + stimer_start(stimer);
> + } else
> + stimer_cleanup(stimer);

Minor nitpick: it's better (and afair required by coding style) to use
'{}' for both branches here:

if (stimer->config.enable && stimer->count) {
if (!stimer->msg_pending)
stimer_start(stimer);
} else {
stimer_cleanup(stimer);
}

> + }
> }
>
> void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu)

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly