From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31337C04AB4 for ; Fri, 17 May 2019 19:44:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EA1D2204EC for ; Fri, 17 May 2019 19:44:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729340AbfEQTow (ORCPT ); Fri, 17 May 2019 15:44:52 -0400 Received: from mga02.intel.com ([134.134.136.20]:49478 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726851AbfEQTov (ORCPT ); Fri, 17 May 2019 15:44:51 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 May 2019 12:44:51 -0700 X-ExtLoop1: 1 Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.36]) by orsmga007.jf.intel.com with ESMTP; 17 May 2019 12:44:50 -0700 Date: Fri, 17 May 2019 12:44:50 -0700 From: Sean Christopherson To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Liran Alon Subject: Re: [PATCH v3 4/5] KVM: LAPIC: Delay trace advance expire delta Message-ID: <20190517194450.GH15006@linux.intel.com> References: <1557975980-9875-1-git-send-email-wanpengli@tencent.com> <1557975980-9875-5-git-send-email-wanpengli@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1557975980-9875-5-git-send-email-wanpengli@tencent.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 16, 2019 at 11:06:19AM +0800, Wanpeng Li wrote: > From: Wanpeng Li > > wait_lapic_expire() call was moved above guest_enter_irqoff() because of > its tracepoint, which violated the RCU extended quiescent state invoked > by guest_enter_irqoff()[1][2]. This patch simply moves the tracepoint > below guest_exit_irqoff() in vcpu_enter_guest(). Snapshot the delta before > VM-Enter, but trace it after VM-Exit. This can help us to move > wait_lapic_expire() just before vmentry in the later patch. > > [1] Commit 8b89fe1f6c43 ("kvm: x86: move tracepoints outside extended quiescent state") > [2] https://patchwork.kernel.org/patch/7821111/ > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Sean Christopherson > Cc: Liran Alon > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/lapic.c | 16 ++++++++-------- > arch/x86/kvm/lapic.h | 1 + > arch/x86/kvm/x86.c | 2 ++ > 3 files changed, 11 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 2f364fe..af38ece 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1502,27 +1502,27 @@ static inline void __wait_lapic_expire(struct kvm_vcpu *vcpu, u64 guest_cycles) > } > > static inline void adaptive_tune_timer_advancement(struct kvm_vcpu *vcpu, > - u64 guest_tsc, u64 tsc_deadline) > + s64 advance_expire_delta) > { > struct kvm_lapic *apic = vcpu->arch.apic; > u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns; > u64 ns; > > /* too early */ > - if (guest_tsc < tsc_deadline) { > - ns = (tsc_deadline - guest_tsc) * 1000000ULL; > + if (advance_expire_delta < 0) { > + ns = -advance_expire_delta * 1000000ULL; > do_div(ns, vcpu->arch.virtual_tsc_khz); > timer_advance_ns -= min((u32)ns, > timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); > } else { > /* too late */ > - ns = (guest_tsc - tsc_deadline) * 1000000ULL; > + ns = advance_expire_delta * 1000000ULL; > do_div(ns, vcpu->arch.virtual_tsc_khz); > timer_advance_ns += min((u32)ns, > timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); > } > > - if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) > + if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) > apic->lapic_timer.timer_advance_adjust_done = true; > if (unlikely(timer_advance_ns > 5000)) { > timer_advance_ns = 0; > @@ -1545,13 +1545,13 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu) > tsc_deadline = apic->lapic_timer.expired_tscdeadline; > apic->lapic_timer.expired_tscdeadline = 0; > guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc()); > - trace_kvm_wait_lapic_expire(vcpu->vcpu_id, guest_tsc - tsc_deadline); > + apic->lapic_timer.advance_expire_delta = guest_tsc - tsc_deadline; > > - if (guest_tsc < tsc_deadline) > + if (apic->lapic_timer.advance_expire_delta < 0) I'd prefer to keep "guest_tsc < tsc_deadline" here, just so that it's obvious that the call to __wait_lapic_expire() is safe. My eyes did a few double takes reading this code :-) > __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); > > if (unlikely(!apic->lapic_timer.timer_advance_adjust_done)) > - adaptive_tune_timer_advancement(vcpu, guest_tsc, tsc_deadline); > + adaptive_tune_timer_advancement(vcpu, apic->lapic_timer.advance_expire_delta); > } > > static void start_sw_tscdeadline(struct kvm_lapic *apic) > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h > index d6d049b..3e72a25 100644 > --- a/arch/x86/kvm/lapic.h > +++ b/arch/x86/kvm/lapic.h > @@ -32,6 +32,7 @@ struct kvm_timer { > u64 tscdeadline; > u64 expired_tscdeadline; > u32 timer_advance_ns; > + s64 advance_expire_delta; > atomic_t pending; /* accumulated triggered timers */ > bool hv_timer_in_use; > bool timer_advance_adjust_done; > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index f2e3847..4a7b00c 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7961,6 +7961,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > ++vcpu->stat.exits; > > guest_exit_irqoff(); > + trace_kvm_wait_lapic_expire(vcpu->vcpu_id, > + vcpu->arch.apic->lapic_timer.advance_expire_delta); This needs to be guarded with lapic_in_kernel(vcpu). But, since this is all in the same flow, a better approach would be to return the delta from wait_lapic_expire(). That saves 8 bytes in struct kvm_timer and avoids additional checks for tracing the delta. E.g.: s64 lapic_expire_delta; ... if (lapic_in_kernel(vcpu) && vcpu->arch.apic->lapic_timer.timer_advance_ns) lapic_expire_delta = wait_lapic_expire(vcpu); else lapic_expire_delta = 0; ... trace_kvm_wait_lapic_expire(vcpu->vcpu_id, lapic_expire_delta); > > local_irq_enable(); > preempt_enable(); > -- > 2.7.4 >