Messages in this thread Patch in this message |  | | Date | Fri, 11 Feb 2022 09:47:03 -0800 | From | Yury Norov <> | Subject | Re: [PATCH 07/49] KVM: x86: replace bitmap_weight with bitmap_empty where appropriate |
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On Fri, Feb 11, 2022 at 05:19:36PM +0000, Sean Christopherson wrote: > On Fri, Feb 11, 2022, Christophe JAILLET wrote: > > Le 10/02/2022 à 23:48, Yury Norov a écrit : > > > 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> > > > Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.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..06c2a5603123 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 think that you can also remove the "!" here, ... > > > > > 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); > > > > ... and there... > > > > > - if (!!auto_eoi_old == !!auto_eoi_new) > > > + if (auto_eoi_old == auto_eoi_new) > > > > ... because this test would still give the same result.
This is how it was in v3. Vitaly asked to add '!' to keep variables names correct. https://lore.kernel.org/lkml/CAAH8bW_u6oNOkMsA_jRyWFHkzjMi0CB7gXmvLYAdjNMSqrrY7w@mail.gmail.com/t/#m51d28c03eafed5754a69f95f24c7d0a0510cc5c0 > > It would give the same result, but the variable names would be inverted as they > track if "auto EOI" is being used. So yes, it's technically unnecessary, but > also very deliberate.
auto_eoi_old_not_used = bitmap_empty() is worse to me than auto_eoi_old = !bitmap_empty().
Thanks, Yury
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