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 <[email protected]> Cc: Haiwei Li <[email protected]> Suggested-by: Paolo Bonzini <[email protected]> Signed-off-by: Wanpeng Li <[email protected]> Message-Id: <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
ambv · May 15, 2020 · 379a3c8 · 379a3c8
1 parent 404d5d7
commit 379a3c8
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Showing 2 changed files with 5 additions and 1 deletion.
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
@@ -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;

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -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.
-Original file line number
+Diff line change
@@ Expand Up / @@ -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.
@@ Expand Down @@