linux-kernel - [PATCH v3 1/2] KVM: X86: Less kvmclock sync induced vmexits after VM boots

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Date:   Mon, 17 Feb 2020 18:36:41 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH v3 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>
---
 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 (kvm->created_vcpus == 1)
+        schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
+                        KVMCLOCK_SYNC_PERIOD);
 }

 void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
--
2.7.4