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KVM: X86: Micro-optimize IPI fastpath delay 

This patch optimizes the virtual IPI fastpath emulation sequence:

write ICR2                          send virtual IPI
read ICR2                           write ICR2
send virtual IPI         ==>        write ICR
write ICR

We can observe ~0.67% performance improvement for IPI microbenchmark
(https://lore.kernel.org/kvm/20171219085010.4081-1-ynorov@caviumnetworks.com/)
on Skylake server.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1585189202-1708-4-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Wanpeng Li 2020-03-26 10:20:02 +08:00 committed by Paolo Bonzini
parent 8a1038de11
commit d5361678e6
3 changed files with 8 additions and 3 deletions
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4
arch/x86/kvm/lapic.c
View File

@ -1241,7 +1241,7 @@ void kvm_apic_set_eoi_accelerated(struct kvm_vcpu *vcpu, int vector)
}
EXPORT_SYMBOL_GPL(kvm_apic_set_eoi_accelerated);
static void apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high)
void kvm_apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high)
{
struct kvm_lapic_irq irq;
@ -1955,7 +1955,7 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
case APIC_ICR:
/* No delay here, so we always clear the pending bit */
val &= ~(1 << 12);
apic_send_ipi(apic, val, kvm_lapic_get_reg(apic, APIC_ICR2));
kvm_apic_send_ipi(apic, val, kvm_lapic_get_reg(apic, APIC_ICR2));
kvm_lapic_set_reg(apic, APIC_ICR, val);
break;

1
arch/x86/kvm/lapic.h
View File

@ -96,6 +96,7 @@ void kvm_apic_update_apicv(struct kvm_vcpu *vcpu);
bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
struct kvm_lapic_irq *irq, int *r, struct dest_map *dest_map);
void kvm_apic_send_ipi(struct kvm_lapic *apic, u32 icr_low, u32 icr_high);
u64 kvm_get_apic_base(struct kvm_vcpu *vcpu);
int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info);

6
arch/x86/kvm/x86.c
View File

@ -1585,8 +1585,12 @@ static int handle_fastpath_set_x2apic_icr_irqoff(struct kvm_vcpu *vcpu, u64 data
((data & APIC_DEST_MASK) == APIC_DEST_PHYSICAL) &&
((data & APIC_MODE_MASK) == APIC_DM_FIXED)) {
data &= ~(1 << 12);
kvm_apic_send_ipi(vcpu->arch.apic, (u32)data, (u32)(data >> 32));
kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR2, (u32)(data >> 32));
return kvm_lapic_reg_write(vcpu->arch.apic, APIC_ICR, (u32)data);
kvm_lapic_set_reg(vcpu->arch.apic, APIC_ICR, (u32)data);
trace_kvm_apic_write(APIC_ICR, (u32)data);
return 0;
}
return 1;