merge pv_eoi_get_pending and pv_eoi_clr_pending into a single
function pv_eoi_test_and_clear_pending, which returns and clear
the value of the pending bit.
and clear pv eoi pending bit only when it is set, to avoid calling
pv_eoi_put_user(), this can speed about 300 nsec on AMD EPYC most
of the time
Suggested-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
---
diff v2: merge as pv_eoi_test_and_clear_pending
diff v3: remove printk in a new patch
diff v4: fix comments place
arch/x86/kvm/lapic.c | 40 +++++++++++++++++++---------------------
1 files changed, 19 insertions(+), 21 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 752c48e..b1de23e 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -673,15 +673,6 @@ static inline bool pv_eoi_enabled(struct kvm_vcpu *vcpu)
return vcpu->arch.pv_eoi.msr_val & KVM_MSR_ENABLED;
}
-static bool pv_eoi_get_pending(struct kvm_vcpu *vcpu)
-{
- u8 val;
- if (pv_eoi_get_user(vcpu, &val) < 0)
- return false;
-
- return val & KVM_PV_EOI_ENABLED;
-}
-
static void pv_eoi_set_pending(struct kvm_vcpu *vcpu)
{
if (pv_eoi_put_user(vcpu, KVM_PV_EOI_ENABLED) < 0)
@@ -690,12 +681,26 @@ static void pv_eoi_set_pending(struct kvm_vcpu *vcpu)
__set_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention);
}
-static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
+static bool pv_eoi_test_and_clr_pending(struct kvm_vcpu *vcpu)
{
- if (pv_eoi_put_user(vcpu, KVM_PV_EOI_DISABLED) < 0)
- return;
+ u8 val;
+
+ if (pv_eoi_get_user(vcpu, &val) < 0)
+ return false;
+
+ val &= KVM_PV_EOI_ENABLED;
+
+ if (val && pv_eoi_put_user(vcpu, KVM_PV_EOI_DISABLED) < 0)
+ return false;
+ /*
+ * Clear pending bit in any case: it will be set again on vmentry.
+ * While this might not be ideal from performance point of view,
+ * this makes sure pv eoi is only enabled when we know it's safe.
+ */
__clear_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention);
+
+ return val;
}
static int apic_has_interrupt_for_ppr(struct kvm_lapic *apic, u32 ppr)
@@ -2671,7 +2676,6 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
static void apic_sync_pv_eoi_from_guest(struct kvm_vcpu *vcpu,
struct kvm_lapic *apic)
{
- bool pending;
int vector;
/*
* PV EOI state is derived from KVM_APIC_PV_EOI_PENDING in host
@@ -2685,14 +2689,8 @@ static void apic_sync_pv_eoi_from_guest(struct kvm_vcpu *vcpu,
* -> host enabled PV EOI, guest executed EOI.
*/
BUG_ON(!pv_eoi_enabled(vcpu));
- pending = pv_eoi_get_pending(vcpu);
- /*
- * Clear pending bit in any case: it will be set again on vmentry.
- * While this might not be ideal from performance point of view,
- * this makes sure pv eoi is only enabled when we know it's safe.
- */
- pv_eoi_clr_pending(vcpu);
- if (pending)
+
+ if (pv_eoi_test_and_clr_pending(vcpu))
return;
vector = apic_set_eoi(apic);
trace_kvm_pv_eoi(apic, vector);
--
1.7.1
