From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752476AbdGBBfh (ORCPT ); Sat, 1 Jul 2017 21:35:37 -0400 Received: from mail-oi0-f68.google.com ([209.85.218.68]:36730 "EHLO mail-oi0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752384AbdGBBfa (ORCPT ); Sat, 1 Jul 2017 21:35:30 -0400 MIME-Version: 1.0 In-Reply-To: <1498755501-39602-4-git-send-email-pbonzini@redhat.com> References: <1498755501-39602-1-git-send-email-pbonzini@redhat.com> <1498755501-39602-4-git-send-email-pbonzini@redhat.com> From: Wanpeng Li Date: Sun, 2 Jul 2017 09:35:29 +0800 Message-ID: Subject: Re: [PATCH 3/3] KVM: LAPIC: Fix lapic timer injection delay To: Paolo Bonzini Cc: "linux-kernel@vger.kernel.org" , kvm , Radim Krcmar , Wanpeng Li Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v621ZwKd028127 2017-06-30 0:58 GMT+08:00 Paolo Bonzini : > 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. > The next vmentry results in an immediate vmx preemption timer vmexit > and 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 ~1200 cycles on > the tscdeadline_immed test of vmexit.flat. > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Signed-off-by: Wanpeng Li > [Rebased on top of previous patch. - Paolo] > Signed-off-by: Paolo Bonzini > --- > arch/x86/kvm/lapic.c | 5 ++++- > arch/x86/kvm/vmx.c | 3 ++- > 2 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index a80e5a5d6f2f..2819d4c123eb 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1525,8 +1525,11 @@ static bool start_hv_timer(struct kvm_lapic *apic) > * the window. For periodic timer, leave the hv timer running for > * simplicity, and the deadline will be recomputed on the next vmexit. > */ > - if (!apic_lvtt_period(apic) && atomic_read(&ktimer->pending)) > + if (!apic_lvtt_period(apic) && (r || atomic_read(&ktimer->pending))) { > + if (r) > + apic_timer_expired(apic); > return false; > + } This logic is not the same as in my v4 http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1434040.html . You return false for the expired timer and actually it will switch to sw timer. > > trace_kvm_hv_timer_state(apic->vcpu->vcpu_id, true); > return true; > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index e8b61ad84a8e..92ddea08f999 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -11147,7 +11147,8 @@ 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; > + > + return delta_tsc == 0; > } > > static void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu) > -- > 1.8.3.1 >