Commit 379a3c8e authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
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KVM: VMX: Optimize posted-interrupt delivery for timer fastpath 



While optimizing posted-interrupt delivery especially for the timer
fastpath scenario, I measured kvm_x86_ops.deliver_posted_interrupt()
to introduce substantial latency because the processor has to perform
all vmentry tasks, ack the posted interrupt notification vector,
read the posted-interrupt descriptor etc.

This is not only slow, it is also unnecessary when delivering an
interrupt to the current CPU (as is the case for the LAPIC timer) because
PIR->IRR and IRR->RVI synchronization is already performed on vmentry
Therefore skip kvm_vcpu_trigger_posted_interrupt in this case, and
instead do vmx_sync_pir_to_irr() on the EXIT_FASTPATH_REENTER_GUEST
fastpath as well.

Tested-by: default avatarHaiwei Li <lihaiwei@tencent.com>
Cc: Haiwei Li <lihaiwei@tencent.com>
Suggested-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarWanpeng Li <wanpengli@tencent.com>
Message-Id: <1588055009-12677-6-git-send-email-wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 404d5d7b

arch/x86/kvm/vmx/vmx.c

+4 −1
Original line number Diff line number Diff line
@@ -3936,7 +3936,8 @@ static int vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector) 
	if (pi_test_and_set_on(&vmx->pi_desc))

		return 0;



	if (!kvm_vcpu_trigger_posted_interrupt(vcpu, false))

	if (vcpu != kvm_get_running_vcpu() &&

	    !kvm_vcpu_trigger_posted_interrupt(vcpu, false))

		kvm_vcpu_kick(vcpu);



	return 0;
@@ -6812,6 +6813,8 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu) 
			 * but it would incur the cost of a retpoline for now.

			 * Revisit once static calls are available.

			 */

			if (vcpu->arch.apicv_active)

				vmx_sync_pir_to_irr(vcpu);

			goto reenter_guest;

		}

		exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;

virt/kvm/kvm_main.c

+1 −0
Original line number Diff line number Diff line
@@ -4646,6 +4646,7 @@ struct kvm_vcpu *kvm_get_running_vcpu(void) 


	return vcpu;

}

EXPORT_SYMBOL_GPL(kvm_get_running_vcpu);



/**

 * kvm_get_running_vcpus - get the per-CPU array of currently running vcpus.