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([2001:b07:6468:f312:102b:3795:6714:7df6]) by smtp.gmail.com with ESMTPSA id o11sm2591258wmc.7.2019.09.11.08.45.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Sep 2019 08:45:20 -0700 (PDT) Subject: Re: [PATCH v3 1/2] KVM: LAPIC: Tune lapic_timer_advance_ns smoothly To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= References: <1566980342-22045-1-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: Date: Wed, 11 Sep 2019 17:45:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1566980342-22045-1-git-send-email-wanpengli@tencent.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/08/19 10:19, Wanpeng Li wrote: > From: Wanpeng Li > > Using a moving average based on per-vCPU lapic_timer_advance_ns to tune > smoothly, filter out drastic fluctuation which prevents this before, > let's assume it is 10000 cycles. > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/lapic.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index e904ff0..181537a 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -69,6 +69,7 @@ > #define LAPIC_TIMER_ADVANCE_ADJUST_INIT 1000 > /* step-by-step approximation to mitigate fluctuation */ > #define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8 > +#define LAPIC_TIMER_ADVANCE_FILTER 10000 > > static inline int apic_test_vector(int vec, void *bitmap) > { > @@ -1484,23 +1485,28 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu, > s64 advance_expire_delta) > { > struct kvm_lapic *apic = vcpu->arch.apic; > - u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns; > - u64 ns; > + u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns, ns; > + > + if (abs(advance_expire_delta) > LAPIC_TIMER_ADVANCE_FILTER) > + /* filter out drastic fluctuations */ > + return; > > /* too early */ > 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); > + timer_advance_ns -= ns; > } else { > /* too late */ > 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); > + timer_advance_ns += ns; > } > > + timer_advance_ns = (apic->lapic_timer.timer_advance_ns * > + (LAPIC_TIMER_ADVANCE_ADJUST_STEP - 1) + advance_expire_delta) / > + LAPIC_TIMER_ADVANCE_ADJUST_STEP; > + > if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) > apic->lapic_timer.timer_advance_adjust_done = true; > if (unlikely(timer_advance_ns > 5000)) { > This looks great. But instead of patch 2, why not remove timer_advance_adjust_done altogether? Paolo