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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2DCAC433EF for ; Fri, 8 Oct 2021 10:52:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D3CA760560 for ; Fri, 8 Oct 2021 10:52:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239954AbhJHKyq (ORCPT ); Fri, 8 Oct 2021 06:54:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:27056 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230042AbhJHKyp (ORCPT ); Fri, 8 Oct 2021 06:54:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633690370; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bXeqaJQRHIjGRFMe5JQ357RA8p6YK7boOm1VSZD5rnM=; b=KH7WQFZ4TR5wPOQJQZYVEKLIpSOiz3Ha9KwW0hiFA25EYouO7br+2dVu5EiYS5KpHBusza gSGzgqp2hIFDLvaSBpIkR3eeRBzsenqC/7cnW+4iTQT/cupAs9KnuOv2OwxDKP9mlQYL2g OSf4CNgB6fbPKCHjrKjbKmOrqGbO7vo= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-468-PUiAiDHFOO2tioza04746Q-1; Fri, 08 Oct 2021 06:52:49 -0400 X-MC-Unique: PUiAiDHFOO2tioza04746Q-1 Received: by mail-wr1-f71.google.com with SMTP id c4-20020a5d6cc4000000b00160edc8bb28so1203939wrc.9 for ; Fri, 08 Oct 2021 03:52:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=bXeqaJQRHIjGRFMe5JQ357RA8p6YK7boOm1VSZD5rnM=; b=NIwLLKYDaILfK34uI+i79I4lR8smB4FJkPM+yKfS6t3h3aPcuQxoXRus9Knj8THdLJ GabRq0wddu6AaCSLLoFeMPkhHYjVrKRzQB8NuL4Lo73M5hKba4T9nrK6Js97P/2rMAfL nnyoyQChDTyii2ycZwie/akAYXO9kLXUy+MUGZGOAJOCAN6VAtOMZ3fxA+Y+ZXBM1flz SB5wlnjVWQpTQD/A5SN95sRV01sS2I9q28jzeY9HmIdeZgnshMA9XxuFH9tNX8CuBkuI DLkhWiZ6beJP3hBHH8yp3orBM58GYQhmkqYVEU2fGeWwf7X5Z/5dyRHk3+KgzVtz4+hK g0lg== X-Gm-Message-State: AOAM531pStDAaUmOw7E4qY+0b/rhOTQRsLub5O+MMzpT6WtMgXYziAgw TehjLegjO0yp/7crXXrVgoN3VE2E9vtzdTLvfKWH3TwxUm4+LSKGnyupGKOI4fkJ2dFy5v0mLkV 2RGYylPY/OlZl X-Received: by 2002:a5d:47cd:: with SMTP id o13mr3165139wrc.85.1633690368296; Fri, 08 Oct 2021 03:52:48 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx95/KS3DNJ5vz5xhS/EN/yS2kB8/wbXBtifrJL81st7o9TE+bwlPVJ+PXLSKHW5fXBOiyYkw== X-Received: by 2002:a5d:47cd:: with SMTP id o13mr3165124wrc.85.1633690368144; Fri, 08 Oct 2021 03:52:48 -0700 (PDT) Received: from vitty.brq.redhat.com (g-server-2.ign.cz. [91.219.240.2]) by smtp.gmail.com with ESMTPSA id e1sm2228739wru.26.2021.10.08.03.52.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 Oct 2021 03:52:47 -0700 (PDT) From: Vitaly Kuznetsov To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [PATCH 3/3] KVM: LAPIC: Optimize PMI delivering overhead In-Reply-To: <1633687054-18865-3-git-send-email-wanpengli@tencent.com> References: <1633687054-18865-1-git-send-email-wanpengli@tencent.com> <1633687054-18865-3-git-send-email-wanpengli@tencent.com> Date: Fri, 08 Oct 2021 12:52:46 +0200 Message-ID: <87ily73i0x.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Wanpeng Li writes: > From: Wanpeng Li > > The overhead of kvm_vcpu_kick() is huge since expensive rcu/memory > barrier etc operations in rcuwait_wake_up(). It is worse when local > delivery since the vCPU is scheduled and we still suffer from this. > We can observe 12us+ for kvm_vcpu_kick() in kvm_pmu_deliver_pmi() > path by ftrace before the patch and 6us+ after the optimization. > > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/lapic.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 76fb00921203..ec6997187c6d 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1120,7 +1120,8 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode, > case APIC_DM_NMI: > result = 1; > kvm_inject_nmi(vcpu); > - kvm_vcpu_kick(vcpu); > + if (vcpu != kvm_get_running_vcpu()) > + kvm_vcpu_kick(vcpu); Out of curiosity, can this be converted into a generic optimization for kvm_vcpu_kick() instead? I.e. if kvm_vcpu_kick() is called for the currently running vCPU, there's almost nothing to do, especially when we already have a request pending, right? (I didn't put too much though to it) > break; > > case APIC_DM_INIT: -- Vitaly