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([2001:b07:6468:f312:ac04:eef9:b257:b844]) by smtp.gmail.com with ESMTPSA id z21sm4111391wmf.25.2019.05.20.04.14.29 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 May 2019 04:14:29 -0700 (PDT) Subject: Re: [PATCH v4 4/5] KVM: LAPIC: Delay trace advance expire delta To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Sean Christopherson , Liran Alon References: <1558340289-6857-1-git-send-email-wanpengli@tencent.com> <1558340289-6857-5-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Message-ID: Date: Mon, 20 May 2019 13:14:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <1558340289-6857-5-git-send-email-wanpengli@tencent.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/05/19 10:18, 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/ This is a bit confusing, since the delta is printed after the corresponding vmexit but the wait is done before the vmentry. I think we can drop the tracepoint: ------------- 8< ---------------- >From ae148d98d49b96b5222e2c78ac1b1e13cc526d71 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 20 May 2019 13:10:01 +0200 Subject: [PATCH] KVM: lapic: replace wait_lapic_expire tracepoint with restart_apic_timer 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]. We would like to move wait_lapic_expire() just before vmentry, which would place wait_lapic_expire() again inside the extended quiescent state. Drop the tracepoint, but add instead another one that can be useful and where we can check the status of the adaptive tuning procedure. [1] Commit 8b89fe1f6c43 ("kvm: x86: move tracepoints outside extended quiescent state") [2] https://patchwork.kernel.org/patch/7821111/ Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 4 +++- arch/x86/kvm/trace.h | 15 +++++++-------- 2 files changed, 10 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index c12b090f4fad..8f05c1d0b486 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1545,7 +1545,6 @@ 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); if (guest_tsc < tsc_deadline) __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); @@ -1763,6 +1762,9 @@ static void start_sw_timer(struct kvm_lapic *apic) static void restart_apic_timer(struct kvm_lapic *apic) { + trace_kvm_restart_apic_timer(apic->vcpu->vcpu_id, + apic->lapic_timer.timer_advance_ns); + preempt_disable(); if (!apic_lvtt_period(apic) && atomic_read(&apic->lapic_timer.pending)) diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h index 4d47a2631d1f..f6e000038f3f 100644 --- a/arch/x86/kvm/trace.h +++ b/arch/x86/kvm/trace.h @@ -953,24 +953,23 @@ __entry->flags) ); -TRACE_EVENT(kvm_wait_lapic_expire, - TP_PROTO(unsigned int vcpu_id, s64 delta), - TP_ARGS(vcpu_id, delta), +TRACE_EVENT(kvm_restart_apic_timer, + TP_PROTO(unsigned int vcpu_id, u32 advance), + TP_ARGS(vcpu_id, advance), TP_STRUCT__entry( __field( unsigned int, vcpu_id ) - __field( s64, delta ) + __field( u32, advance ) ), TP_fast_assign( __entry->vcpu_id = vcpu_id; - __entry->delta = delta; + __entry->advance = advance; ), - TP_printk("vcpu %u: delta %lld (%s)", + TP_printk("vcpu %u: advance %u", __entry->vcpu_id, - __entry->delta, - __entry->delta < 0 ? "early" : "late") + __entry->advance) ); TRACE_EVENT(kvm_enter_smm,