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([2001:b07:6468:f312:59c7:c3ee:2dec:d2b4]) by smtp.gmail.com with ESMTPSA id c15sm6405828wrt.1.2020.02.18.07.33.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Feb 2020 07:33:46 -0800 (PST) Subject: Re: [PATCH v4 1/2] KVM: X86: Less kvmclock sync induced vmexits after VM boots To: Vitaly Kuznetsov , Wanpeng Li Cc: Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1581988630-19182-1-git-send-email-wanpengli@tencent.com> <87r1ys7xpk.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Message-ID: Date: Tue, 18 Feb 2020 16:33:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <87r1ys7xpk.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 18/02/20 15:54, Vitaly Kuznetsov wrote: >> - 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). No, it executes after 5 minutes. I agree that the patch shouldn't be really necessary, though you do save on cacheline bouncing due to test_and_set_bit. Paolo > Do we actually happen to finish executing it before next vCPU > is created or why does the storm you describe happens?