Commit d5361678 authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
Browse files

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: default avatarWanpeng Li <wanpengli@tencent.com>
Message-Id: <1585189202-1708-4-git-send-email-wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 8a1038de

arch/x86/kvm/lapic.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

arch/x86/kvm/lapic.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/x86.c

+5 −1
Original line number Diff line number Diff line
@@ -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;

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