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=-8.3 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_SANE_1 autolearn=unavailable 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 C7A13C49ED7 for ; Mon, 16 Sep 2019 18:55:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AA93320830 for ; Mon, 16 Sep 2019 18:55:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727962AbfIPSzx (ORCPT ); Mon, 16 Sep 2019 14:55:53 -0400 Received: from mga11.intel.com ([192.55.52.93]:17475 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725912AbfIPSzx (ORCPT ); Mon, 16 Sep 2019 14:55:53 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Sep 2019 11:55:51 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,513,1559545200"; d="scan'208";a="187228691" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by fmsmga007.fm.intel.com with ESMTP; 16 Sep 2019 11:55:51 -0700 Date: Mon, 16 Sep 2019 11:55:51 -0700 From: Sean Christopherson To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [PATCH v4] KVM: LAPIC: Tune lapic_timer_advance_ns smoothly Message-ID: <20190916185551.GL18871@linux.intel.com> References: <1568623199-5294-1-git-send-email-wanpengli@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1568623199-5294-1-git-send-email-wanpengli@tencent.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 16, 2019 at 04:39:59PM +0800, Wanpeng Li wrote: > From: Wanpeng Li > > Filter out drastic fluctuation and random fluctuation, remove > timer_advance_adjust_done altogether, the adjustment would be > continuous. > > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/lapic.c | 26 ++++++++++++-------------- > arch/x86/kvm/lapic.h | 1 - > arch/x86/kvm/x86.c | 2 +- > arch/x86/kvm/x86.h | 1 + > 4 files changed, 14 insertions(+), 16 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index dbbe478..2585b86 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 5000 > > static inline int apic_test_vector(int vec, void *bitmap) > { > @@ -1482,29 +1483,28 @@ 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; Is changing 'ns' to a u32 intentionaly? It's still cast to a u32 in the calculations, and set from @advance_expire_delta. > + > + if (abs(advance_expire_delta) > LAPIC_TIMER_ADVANCE_FILTER || Shouldn't LAPIC_TIMER_ADVANCE_FILTER be used in the other "if ... > 5000" check? if (unlikely(timer_advance_ns > 5000)) And maybe name it LAPIC_TIMER_ADVANCE_MAX or something? > + abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) { This should be aligned with the other 'abs', e.g.: if (abs(...) || abs(...)) return > + /* filter out random fluctuations */ If you put the comment above the if statement then you can drop the parentheses. And if you're going to bother with a comment, maybe be a bit more explicit? E.g.: /* Do not adjust for tiny fluctuations or large random spikes. */ if (abs(...) || abs(...)) return; > + 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/LAPIC_TIMER_ADVANCE_ADJUST_STEP; > } 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/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)) { > + if (unlikely(timer_advance_ns > 5000)) > timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT; > - apic->lapic_timer.timer_advance_adjust_done = false; > - } > apic->lapic_timer.timer_advance_ns = timer_advance_ns; > } > > @@ -1524,7 +1524,7 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) > if (guest_tsc < tsc_deadline) > __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); > > - if (unlikely(!apic->lapic_timer.timer_advance_adjust_done)) > + if (lapic_timer_advance_ns == -1) Rather than expose 'lapic_timer_advance_ns' from x86.c, what if we add a 'static bool dynamically_adjust_timer_advance __read_mostly;' in lapic.c, and have that be set in kvm_create_lapic() and checked here? That'd make this code a little more readable, would make this patch more obvious (it wasn't immediately clear why lapic_timer_advance_ns was being exposed), and would reduce the probability of unintentionally writing/corrupting the module param. > adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta); > } > > @@ -2302,10 +2302,8 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns) > apic->lapic_timer.timer.function = apic_timer_fn; > if (timer_advance_ns == -1) { > apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT; > - apic->lapic_timer.timer_advance_adjust_done = false; > } else { > apic->lapic_timer.timer_advance_ns = timer_advance_ns; > - apic->lapic_timer.timer_advance_adjust_done = true; > } Parentheses can be dropped (unless this is converted to a local global, as above). > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h > index 50053d2..2aad7e2 100644 > --- a/arch/x86/kvm/lapic.h > +++ b/arch/x86/kvm/lapic.h > @@ -35,7 +35,6 @@ struct kvm_timer { > s64 advance_expire_delta; > atomic_t pending; /* accumulated triggered timers */ > bool hv_timer_in_use; > - bool timer_advance_adjust_done; > }; > > struct kvm_lapic { > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 83288ba..bb4574c 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -141,7 +141,7 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR); > * advancement entirely. Any other value is used as-is and disables adaptive > * tuning, i.e. allows priveleged userspace to set an exact advancement time. > */ > -static int __read_mostly lapic_timer_advance_ns = -1; > +int __read_mostly lapic_timer_advance_ns = -1; > module_param(lapic_timer_advance_ns, int, S_IRUGO | S_IWUSR); > > static bool __read_mostly vector_hashing = true; > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h > index b5274e2..1bf2d82 100644 > --- a/arch/x86/kvm/x86.h > +++ b/arch/x86/kvm/x86.h > @@ -301,6 +301,7 @@ extern unsigned int min_timer_period_us; > > extern bool enable_vmware_backdoor; > > +extern int lapic_timer_advance_ns; > extern int pi_inject_timer; > > extern struct static_key kvm_no_apic_vcpu; > -- > 2.7.4 >