Re: [PATCH] kvm: x86: lapic: remove one redundant judging condition
On 2014/11/5 18:22, Paolo Bonzini wrote: On 05/11/2014 10:03, Tiejun Chen wrote: Finally we always return highest_irr so its unnecessary to return -1 after check if highest_irr == -1. Signed-off-by: Tiejun Chen --- arch/x86/kvm/lapic.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 5f574b4..e6a7eb6 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1638,8 +1638,7 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu) apic_update_ppr(apic); highest_irr = apic_find_highest_irr(apic); - if ((highest_irr == -1) || - ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI))) + if ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI)) return -1; return highest_irr; } I think the code is clearer without this change. The two returns mean: - return -1: no interrupt to inject - return highest_irr: inject this interrupt With IRR equal to all zeroes (highest_irr = -1), your patch would make the "if" always false ("current PPR is low, can inject the interrupt"), but computing highest_irr & 0xF0 would make no sense if highest_irr == -1. Yeah, you're right so here is just a little confusion to read. Actually what this code is doing looks like, @@ -1638,7 +1638,7 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu) apic_update_ppr(apic); highest_irr = apic_find_highest_irr(apic); - if ((highest_irr == -1) || + if ((highest_irr != -1) && ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI))) return -1; return highest_irr; But it's really no big deal so we can keep the original alive. Thanks Tiejun To put it another way, imagine the code looked like this: static inline int int_prio(int vector) { WARN_ON(vector == -1); return vector & 0xF0; } ... apic_update_ppr(apic); highest_irr = apic_find_highest_irr(apic); if (highest_irr == -1 || int_prio(highest_irr) <= kvm_apic_get_reg(apic, APIC_PROCPRI)) return -1; return highest_irr; Then removing the check on highest_irr == -1 would trigger a warning. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] kvm: x86: lapic: remove one redundant judging condition
On 05/11/2014 10:03, Tiejun Chen wrote: > Finally we always return highest_irr so its unnecessary to return -1 > after check if highest_irr == -1. > > Signed-off-by: Tiejun Chen > --- > arch/x86/kvm/lapic.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 5f574b4..e6a7eb6 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1638,8 +1638,7 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu) > > apic_update_ppr(apic); > highest_irr = apic_find_highest_irr(apic); > - if ((highest_irr == -1) || > - ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI))) > + if ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI)) > return -1; > return highest_irr; > } I think the code is clearer without this change. The two returns mean: - return -1: no interrupt to inject - return highest_irr: inject this interrupt With IRR equal to all zeroes (highest_irr = -1), your patch would make the "if" always false ("current PPR is low, can inject the interrupt"), but computing highest_irr & 0xF0 would make no sense if highest_irr == -1. To put it another way, imagine the code looked like this: static inline int int_prio(int vector) { WARN_ON(vector == -1); return vector & 0xF0; } ... apic_update_ppr(apic); highest_irr = apic_find_highest_irr(apic); if (highest_irr == -1 || int_prio(highest_irr) <= kvm_apic_get_reg(apic, APIC_PROCPRI)) return -1; return highest_irr; Then removing the check on highest_irr == -1 would trigger a warning. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH] kvm: x86: lapic: remove one redundant judging condition
Finally we always return highest_irr so its unnecessary to return -1 after check if highest_irr == -1. Signed-off-by: Tiejun Chen --- arch/x86/kvm/lapic.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 5f574b4..e6a7eb6 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1638,8 +1638,7 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu) apic_update_ppr(apic); highest_irr = apic_find_highest_irr(apic); - if ((highest_irr == -1) || - ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI))) + if ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI)) return -1; return highest_irr; } -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html