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[94.39.191.51]) by smtp.googlemail.com with ESMTPSA id d1sm2464355wra.43.2017.06.28.05.10.06 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 28 Jun 2017 05:10:07 -0700 (PDT) Subject: Re: [PATCH v3] KVM: LAPIC: Fix lapic timer injection delay To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li References: <1498613352-4651-1-git-send-email-wanpeng.li@hotmail.com> From: Paolo Bonzini Message-ID: <68c0d7f8-683f-c7fa-b328-e90e8dd9a789@redhat.com> Date: Wed, 28 Jun 2017 14:10:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <1498613352-4651-1-git-send-email-wanpeng.li@hotmail.com> Content-Language: en-US Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 28/06/2017 03:29, Wanpeng Li wrote: > u64 tscdeadline = apic->lapic_timer.tscdeadline; > + int ret = 0; > > if ((atomic_read(&apic->lapic_timer.pending) && > !apic_lvtt_period(apic)) || > - kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) { > + (ret = kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline))) { > if (apic->lapic_timer.hv_timer_in_use) > cancel_hv_timer(apic); > + if (ret == 1) { > + apic_timer_expired(apic); > + return true; > + } The preemption timer can also be used for modes other than TSC deadline. In periodic mode, your patch would miss a call to advance_periodic_target_expiration, which is only called by kvm_lapic_expired_hv_timer. You could use something like this: but I'm afraid of introducing a mutual recursion between start_hv_timer and kvm_lapic_expired_hv_timer. Paolo diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index d24c8742d9b0..15b751aa7625 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1504,21 +1504,26 @@ static void cancel_hv_timer(struct kvm_lapic *apic) static bool start_hv_timer(struct kvm_lapic *apic) { u64 tscdeadline = apic->lapic_timer.tscdeadline; + bool need_cancel = apic->lapic_timer.hv_timer_in_use; + if (!atomic_read(&apic->lapic_timer.pending) || apic_lvtt_period(apic)) { + int r = kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline); + if (r >= 0) { + need_cancel = false; + apic->lapic_timer.hv_timer_in_use = true; + hrtimer_cancel(&apic->lapic_timer.timer); - if ((atomic_read(&apic->lapic_timer.pending) && - !apic_lvtt_period(apic)) || - kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) { - if (apic->lapic_timer.hv_timer_in_use) - cancel_hv_timer(apic); - } else { - apic->lapic_timer.hv_timer_in_use = true; - hrtimer_cancel(&apic->lapic_timer.timer); - - /* In case the sw timer triggered in the window */ - if (atomic_read(&apic->lapic_timer.pending) && - !apic_lvtt_period(apic)) - cancel_hv_timer(apic); + /* In case the sw timer triggered in the window */ + if (atomic_read(&apic->lapic_timer.pending) && + !apic_lvtt_period(apic)) + need_cancel = true; + else if (r) + kvm_lapic_expired_hv_timer(vcpu); + } } + + if (need_cancel) + cancel_hv_timer(apic); + trace_kvm_hv_timer_state(apic->vcpu->vcpu_id, apic->lapic_timer.hv_timer_in_use); return apic->lapic_timer.hv_timer_in_use;