linux-kernel - [PATCH v4 5/7] KVM: VMX: Optimize posted-interrupt delivery for timer fastpath

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Date:   Tue, 28 Apr 2020 14:23:27 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: [PATCH v4 5/7] KVM: VMX: Optimize posted-interrupt delivery for timer fastpath

From: Wanpeng Li <wanpengli@...cent.com>

Optimizing posted-interrupt delivery especially for the timer fastpath
scenario, I observe kvm_x86_ops.deliver_posted_interrupt() has more latency
then vmx_sync_pir_to_irr() in the case of timer fastpath scenario, since
it needs to wait vmentry, after that it can handle external interrupt, ack
the notification vector, read posted-interrupt descriptor etc, it is slower
than evaluate and delivery during vmentry immediately approach. Let's skip
sending interrupt to notify target pCPU and replace by vmx_sync_pir_to_irr()
before each reenter guest.

Tested-by: Haiwei Li <lihaiwei@...cent.com>
Cc: Haiwei Li <lihaiwei@...cent.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/vmx/vmx.c | 12 ++++++++----
 virt/kvm/kvm_main.c    |  1 +
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 24cadf4..ce19b0e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3909,7 +3909,8 @@ 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;
@@ -6777,9 +6778,12 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	vmx_complete_interrupts(vmx);
 
 	exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
-	if (exit_fastpath == EXIT_FASTPATH_REENTER_GUEST &&
-	    kvm_vcpu_exit_request(vcpu))
-		exit_fastpath = EXIT_FASTPATH_NOP;
+	if (exit_fastpath == EXIT_FASTPATH_REENTER_GUEST) {
+		if (!kvm_vcpu_exit_request(vcpu))
+			vmx_sync_pir_to_irr(vcpu);
+		else
+			exit_fastpath = EXIT_FASTPATH_NOP;
+	}
 
 	return exit_fastpath;
 }
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 33e1eee..2482f3c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4644,6 +4644,7 @@ 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.
-- 
2.7.4