From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753403AbdF2O3o (ORCPT ); Thu, 29 Jun 2017 10:29:44 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:34460 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751974AbdF2O3f (ORCPT ); Thu, 29 Jun 2017 10:29:35 -0400 Subject: Re: [PATCH v4] 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: <1498742889-10080-1-git-send-email-wanpeng.li@hotmail.com> From: Paolo Bonzini Message-ID: <2ea28e01-08e2-c2c9-144d-60e930ba14ee@redhat.com> Date: Thu, 29 Jun 2017 16:29:31 +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: <1498742889-10080-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29/06/2017 15:28, Wanpeng Li wrote: > From: Wanpeng Li > > If the TSC deadline timer is programmed really close to the deadline or > even in the past, the computation in vmx_set_hv_timer will program the > absolute target tsc value to vmcs preemption timer field w/ delta == 0, > then plays a vmentry and an upcoming vmx preemption timer fire vmexit > dance, the lapic timer injection is delayed due to this duration. Actually > the lapic timer which is emulated by hrtimer can handle this correctly. > > This patch fixes it by firing the lapic timer and injecting a timer interrupt > immediately during the next vmentry if the TSC deadline timer is programmed > really close to the deadline or even in the past. This saves ~300 cycles on > the tsc_deadline_timer test of apic.flat. > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Signed-off-by: Wanpeng Li Thanks, looks good. I'll post another refactoring of start_hv_timer for comments. And unrelated to your patch, I think we need this: @@ -1567,8 +1575,7 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu *vcpu) return; cancel_hv_timer(apic); - - if (atomic_read(&apic->lapic_timer.pending)) + if (atomic_read(&apic->lapic_timer.pending) && !apic_lvtt_period(apic)) return; if (apic_lvtt_period(apic) || apic_lvtt_oneshot(apic)) Paolo > --- > arch/x86/kvm/lapic.c | 33 ++++++++++++++++++++------------- > arch/x86/kvm/vmx.c | 6 +++++- > 2 files changed, 25 insertions(+), 14 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index d24c874..40ad729 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1504,21 +1504,28 @@ 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); > + > + /* In case the sw timer triggered in the window */ > + if (!apic_lvtt_period(apic)) { > + if (r || atomic_read(&apic->lapic_timer.pending)) { > + need_cancel = true; > + if (r) > + apic_timer_expired(apic); > + } > + } > + } > + } > > - 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); > + if (need_cancel) > + cancel_hv_timer(apic); > > - /* In case the sw timer triggered in the window */ > - if (atomic_read(&apic->lapic_timer.pending) && > - !apic_lvtt_period(apic)) > - 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; > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 4263860..f8ccf8b 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -11158,7 +11158,11 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc) > vmx->hv_deadline_tsc = tscl + delta_tsc; > vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL, > PIN_BASED_VMX_PREEMPTION_TIMER); > - return 0; > + > + if (delta_tsc == 0) > + return 1; > + else > + return 0; > } > > static void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu) >