Messages in this thread | | | From | Vitaly Kuznetsov <> | Subject | Re: [PATCH 06/54] x86/kvm: replace bitmap_weight with bitmap_empty where appropriate | Date | Mon, 24 Jan 2022 10:11:12 +0100 |
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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
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