2023-12-03 19:34:16

by Yury Norov

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

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 <[email protected]>
Signed-off-by: Yury Norov <[email protected]>
---
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);
+ }
}

void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu)
--
2.40.1

2023-12-04 09:53:25

by Vitaly Kuznetsov

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

Yury Norov <[email protected]> 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 <[email protected]>
> Signed-off-by: Yury Norov <[email protected]>
> ---
> 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 <[email protected]>

--
Vitaly

2023-12-04 16:01:22

by Sean Christopherson

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

On Mon, Dec 04, 2023, Vitaly Kuznetsov wrote:
> > - 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)) {

Another nit, please align the indendation:

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:

Yeah, it's a hard requirement in KVM x86.

>
> 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 <[email protected]>
>
> --
> Vitaly
>