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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id a13sm6288184wrp.93.2020.02.18.06.54.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Feb 2020 06:54:16 -0800 (PST) From: Vitaly Kuznetsov To: Wanpeng Li Cc: Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v4 1/2] KVM: X86: Less kvmclock sync induced vmexits after VM boots In-Reply-To: <1581988630-19182-1-git-send-email-wanpengli@tencent.com> References: <1581988630-19182-1-git-send-email-wanpengli@tencent.com> Date: Tue, 18 Feb 2020 15:54:15 +0100 Message-ID: <87r1ys7xpk.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Wanpeng Li writes: > From: Wanpeng Li > > 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 > --- > 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) Forgive me my ignorance, I was under the impression schedule_delayed_work() doesn't do anything if the work is already queued (see queue_delayed_work_on()) and we seem to be scheduling the same work (&kvm->arch.kvmclock_sync_work) which is per-kvm (not per-vcpu). Do we actually happen to finish executing it before next vCPU is created or why does the storm you describe happens? -- Vitaly