linux-kernel - [PATCH v4 1/2] KVM: X86: Less kvmclock sync induced vmexits after VM boots

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Date:   Tue, 18 Feb 2020 09:17:09 +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>
Subject: [PATCH v4 1/2] KVM: X86: Less kvmclock sync induced vmexits after VM boots

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

In the progress of vCPUs creation, it queues a kvmclock sync worker to the global 
workqueue before each vCPU creation completes. Each worker will be scheduled 
after 300 * HZ delay and request a kvmclock update for all vCPUs and kick them 
out. This is especially worse when scaling to large VMs due to a lot of vmexits. 
Just one worker as a leader to trigger the kvmclock sync request for all vCPUs is 
enough.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
v3 -> v4:
 * check vcpu->vcpu_idx

 arch/x86/kvm/x86.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fb5d64e..d0ba2d4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9390,8 +9390,9 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 	if (!kvmclock_periodic_sync)
 		return;
 
-	schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
-					KVMCLOCK_SYNC_PERIOD);
+	if (vcpu->vcpu_idx == 0)
+		schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
+						KVMCLOCK_SYNC_PERIOD);
 }
 
 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
-- 
2.7.4