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KVM: Optimize searching for highest IRR

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Most of the time IRR is empty, so instead of scanning the whole IRR on
each VM entry keep a variable that tells us if IRR is not empty. IRR
will have to be scanned twice on each IRQ delivery, but this is much
more rare than VM entry.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Gleb Natapov
2009-06-11 11:06:51 +03:00
committed by Avi Kivity
parent 6edf14d8d0
commit 33e4c68656
2 changed files with 22 additions and 3 deletions
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24
arch/x86/kvm/lapic.c
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@@ -165,29 +165,46 @@ static int find_highest_vector(void *bitmap)
static inline int apic_test_and_set_irr(int vec, struct kvm_lapic *apic) static inline int apic_test_and_set_irr(int vec, struct kvm_lapic *apic)
{ {
apic->irr_pending = true;
return apic_test_and_set_vector(vec, apic->regs + APIC_IRR); return apic_test_and_set_vector(vec, apic->regs + APIC_IRR);
} }
static inline void apic_clear_irr(int vec, struct kvm_lapic *apic) static inline int apic_search_irr(struct kvm_lapic *apic)
{ {
apic_clear_vector(vec, apic->regs + APIC_IRR); return find_highest_vector(apic->regs + APIC_IRR);
} }
static inline int apic_find_highest_irr(struct kvm_lapic *apic) static inline int apic_find_highest_irr(struct kvm_lapic *apic)
{ {
int result; int result;
result = find_highest_vector(apic->regs + APIC_IRR); if (!apic->irr_pending)
return -1;
result = apic_search_irr(apic);
ASSERT(result == -1 || result >= 16); ASSERT(result == -1 || result >= 16);
return result; return result;
} }
static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)
{
apic->irr_pending = false;
apic_clear_vector(vec, apic->regs + APIC_IRR);
if (apic_search_irr(apic) != -1)
apic->irr_pending = true;
}
int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu) int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu)
{ {
struct kvm_lapic *apic = vcpu->arch.apic; struct kvm_lapic *apic = vcpu->arch.apic;
int highest_irr; int highest_irr;
/* This may race with setting of irr in __apic_accept_irq() and
* value returned may be wrong, but kvm_vcpu_kick() in __apic_accept_irq
* will cause vmexit immediately and the value will be recalculated
* on the next vmentry.
*/
if (!apic) if (!apic)
return 0; return 0;
highest_irr = apic_find_highest_irr(apic); highest_irr = apic_find_highest_irr(apic);
@@ -843,6 +860,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu)
apic_set_reg(apic, APIC_ISR + 0x10 * i, 0); apic_set_reg(apic, APIC_ISR + 0x10 * i, 0);
apic_set_reg(apic, APIC_TMR + 0x10 * i, 0); apic_set_reg(apic, APIC_TMR + 0x10 * i, 0);
} }
apic->irr_pending = false;
update_divide_count(apic); update_divide_count(apic);
atomic_set(&apic->lapic_timer.pending, 0); atomic_set(&apic->lapic_timer.pending, 0);
if (kvm_vcpu_is_bsp(vcpu)) if (kvm_vcpu_is_bsp(vcpu))

1
arch/x86/kvm/lapic.h
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@@ -12,6 +12,7 @@ struct kvm_lapic {
struct kvm_timer lapic_timer; struct kvm_timer lapic_timer;
u32 divide_count; u32 divide_count;
struct kvm_vcpu *vcpu; struct kvm_vcpu *vcpu;
bool irr_pending;
struct page *regs_page; struct page *regs_page;
void *regs; void *regs;
gpa_t vapic_addr; gpa_t vapic_addr;