Commit 379a3c8e authored Apr 28, 2020 by Wanpeng Li Committed by Paolo Bonzini May 15, 2020

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: Haiwei Li <lihaiwei@tencent.com>
Cc: Haiwei Li <lihaiwei@tencent.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1588055009-12677-6-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo 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 @@ reenter_guest:
		* 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.

Admin message