2023-11-18 15:53:20

by Yury Norov

Subject: [PATCH 13/34] KVM: x86: hyper-v: optimize and cleanup kvm_hv_process_stimers()

The function traverses stimer_pending_bitmap n 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
and dropping 2nd check for stimer->config.enable.

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..460e300b558b 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->count) {
+ if (!stimer->msg_pending)
+ stimer_start(stimer);
+ } else
+ stimer_cleanup(stimer);
+ }
}

void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu)
--
2.39.2

2023-11-20 14:27:40

by Vitaly Kuznetsov

Subject: Re: [PATCH 13/34] KVM: x86: hyper-v: optimize and cleanup kvm_hv_process_stimers()

Yury Norov <[email protected]> writes:

> The function traverses stimer_pending_bitmap n 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
> and dropping 2nd check for stimer->config.enable.
>
> 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..460e300b558b 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->count) {

You can't drop 'stimer->config.enable' check here as stimer_expiration()
call above actually changes it. This is done on purpose: oneshot timers
fire only once so 'config.enable' is reset to 0.

> + if (!stimer->msg_pending)
> + stimer_start(stimer);
> + } else
> + stimer_cleanup(stimer);
> + }
> }
>
> void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu)

--
Vitaly

2023-11-21 13:36:35

by Yury Norov

Subject: Re: [PATCH 13/34] KVM: x86: hyper-v: optimize and cleanup kvm_hv_process_stimers()

On Mon, Nov 20, 2023 at 03:26:08PM +0100, Vitaly Kuznetsov wrote:
> Yury Norov <[email protected]> writes:
>
> > The function traverses stimer_pending_bitmap n 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
> > and dropping 2nd check for stimer->config.enable.
> >
> > 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..460e300b558b 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->count) {
>
> You can't drop 'stimer->config.enable' check here as stimer_expiration()
> call above actually changes it. This is done on purpose: oneshot timers
> fire only once so 'config.enable' is reset to 0.

Ok, I see. Will fix in v2