[PATCH 06/54] x86/kvm: replace bitmap_weight with bitmap_empty where appropriate

[PATCH 06/54] x86/kvm: replace bitmap_weight with bitmap_empty where appropriate

[Yury Norov]

In some places kvm/hyperv.c code calls bitmap_weight() to check if any bit
of a given bitmap is set. It's better to use bitmap_empty() in that case
because bitmap_empty() stops traversing the bitmap as soon as it finds
first set bit, while bitmap_weight() counts all bits unconditionally.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
 arch/x86/kvm/hyperv.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 6e38a7d22e97..2c3400dea4b3 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -90,7 +90,7 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,
 {
 	struct kvm_vcpu *vcpu = hv_synic_to_vcpu(synic);
 	struct kvm_hv *hv = to_kvm_hv(vcpu->kvm);
-	int auto_eoi_old, auto_eoi_new;
+	bool auto_eoi_old, auto_eoi_new;
 
 	if (vector < HV_SYNIC_FIRST_VALID_VECTOR)
 		return;
@@ -100,16 +100,16 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,
 	else
 		__clear_bit(vector, synic->vec_bitmap);
 
-	auto_eoi_old = bitmap_weight(synic->auto_eoi_bitmap, 256);
+	auto_eoi_old = bitmap_empty(synic->auto_eoi_bitmap, 256);
 
 	if (synic_has_vector_auto_eoi(synic, vector))
 		__set_bit(vector, synic->auto_eoi_bitmap);
 	else
 		__clear_bit(vector, synic->auto_eoi_bitmap);
 
-	auto_eoi_new = bitmap_weight(synic->auto_eoi_bitmap, 256);
+	auto_eoi_new = bitmap_empty(synic->auto_eoi_bitmap, 256);
 
-	if (!!auto_eoi_old == !!auto_eoi_new)
+	if (auto_eoi_old == auto_eoi_new)
 		return;
 
 	down_write(&vcpu->kvm->arch.apicv_update_lock);
-- 
2.30.2

Re: [PATCH 06/54] x86/kvm: replace bitmap_weight with bitmap_empty where appropriate

[Vitaly Kuznetsov]

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

> In some places kvm/hyperv.c code calls bitmap_weight() to check if any bit
> of a given bitmap is set. It's better to use bitmap_empty() in that case
> because bitmap_empty() stops traversing the bitmap as soon as it finds
> first set bit, while bitmap_weight() counts all bits unconditionally.
>
> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> ---
>  arch/x86/kvm/hyperv.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 6e38a7d22e97..2c3400dea4b3 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -90,7 +90,7 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,
>  {
>  	struct kvm_vcpu *vcpu = hv_synic_to_vcpu(synic);
>  	struct kvm_hv *hv = to_kvm_hv(vcpu->kvm);
> -	int auto_eoi_old, auto_eoi_new;
> +	bool auto_eoi_old, auto_eoi_new;
>  
>  	if (vector < HV_SYNIC_FIRST_VALID_VECTOR)
>  		return;
> @@ -100,16 +100,16 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,
>  	else
>  		__clear_bit(vector, synic->vec_bitmap);
>  
> -	auto_eoi_old = bitmap_weight(synic->auto_eoi_bitmap, 256);
> +	auto_eoi_old = bitmap_empty(synic->auto_eoi_bitmap, 256);

I would've preferred this written as 

	auto_eoi_old = !bitmap_empty(synic->auto_eoi_bitmap, 256);

so the variable would indicate wether AutoEOI was previosly enabled, not
disabled.

>  
>  	if (synic_has_vector_auto_eoi(synic, vector))
>  		__set_bit(vector, synic->auto_eoi_bitmap);
>  	else
>  		__clear_bit(vector, synic->auto_eoi_bitmap);
>  
> -	auto_eoi_new = bitmap_weight(synic->auto_eoi_bitmap, 256);
> +	auto_eoi_new = bitmap_empty(synic->auto_eoi_bitmap, 256);

Same here, of course. "auto_eoi_new = true" sounds like "AutoEOI is now
enabled".

>  
> -	if (!!auto_eoi_old == !!auto_eoi_new)
> +	if (auto_eoi_old == auto_eoi_new)
>  		return;
>  
>  	down_write(&vcpu->kvm->arch.apicv_update_lock);

The change look good to me otherwise, feel free to add

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

-- 
Vitaly