| Message ID | 1415178185-11109-1-git-send-email-tiejun.chen@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <tiejun.chen@intel.com> > --- > 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 <tiejun.chen@intel.com> >> --- >> 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; }
Finally we always return highest_irr so its unnecessary to return -1 after check if highest_irr == -1. Signed-off-by: Tiejun Chen <tiejun.chen@intel.com> --- arch/x86/kvm/lapic.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)