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Subject[PATCH 15/47] KVM: Optimize searching for highest IRR
Date
From: Gleb Natapov <gleb@redhat.com>

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>
---
arch/x86/kvm/lapic.c | 24 +++++++++++++++++++++---
arch/x86/kvm/lapic.h | 1 +
2 files changed, 22 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index b1694dc..3bde43c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -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)
{
+ apic->irr_pending = true;
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)
{
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);

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)
{
struct kvm_lapic *apic = vcpu->arch.apic;
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)
return 0;
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_TMR + 0x10 * i, 0);
}
+ apic->irr_pending = false;
update_divide_count(apic);
atomic_set(&apic->lapic_timer.pending, 0);
if (kvm_vcpu_is_bsp(vcpu))
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index a587f83..3f3ecc6 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -12,6 +12,7 @@ struct kvm_lapic {
struct kvm_timer lapic_timer;
u32 divide_count;
struct kvm_vcpu *vcpu;
+ bool irr_pending;
struct page *regs_page;
void *regs;
gpa_t vapic_addr;
--
1.6.3.3


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