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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 D811EC4320A for ; Fri, 23 Jul 2021 06:12:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE80860E90 for ; Fri, 23 Jul 2021 06:12:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233889AbhGWFbc (ORCPT ); Fri, 23 Jul 2021 01:31:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33510 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229788AbhGWFba (ORCPT ); Fri, 23 Jul 2021 01:31:30 -0400 Received: from mail-oi1-x22f.google.com (mail-oi1-x22f.google.com [IPv6:2607:f8b0:4864:20::22f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E8F3FC061575; Thu, 22 Jul 2021 23:12:03 -0700 (PDT) Received: by mail-oi1-x22f.google.com with SMTP id q6so764070oiw.7; Thu, 22 Jul 2021 23:12:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=AZKNDZPJaYefkpMUKBEqneOnIP2BNDuYsn0cDTJRRE0=; b=JED08zydxY7bsFY4lnM+AZbZVFIX3Yho6mvopHNofOsMP3cVY/W2Cre3f0GHvrgZUE PxdpxVTvd+ejeId7xwiGBX+73F/gc/+rwZcuWNk/XmYRfpI17lbI48VaUCX2wkWZa62Z lZhlDbxzTqgVuHTAuOdmqSP9cIsbDW2z9vcwYlD3n4ISAT7NgOvwkSQC4eA491vVzL5R LpYGfChkod2f0leP7uvDkv11AiJEMys4K4nSTRMkHe6XpiBkO9THtyWW47HoLqlQssAv NZo/UmbepGZ3B+eJzd/FvMMryVD9tzuqttNwT+acYLG93f1nN3TYFcF7tSDefkpxP6fM N/Ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=AZKNDZPJaYefkpMUKBEqneOnIP2BNDuYsn0cDTJRRE0=; b=jW+QB/7mB05WMVvPH1QD2JS5FYwGDgFcrtff6VuJDIdn5UiCoHIQ5oZNqqhRloAcd/ tpbk1//vga/V3j7E5yKiJ0XLoT0H3EYJioGlRWx4cyAFCP5dcmSiZPM3rbE1Zdjw5FMx Q4Ado5SrdH/i56HCjR0A15we9gD3tmV0/WuHTOyrUEPMInOs3KmuwG6lo4ty55jxSso3 5WRgCndUyxVgZJ/L5dPsCqefyRqLahsNaOFR6m9xiD+wQriZebtWYcy86OLU22Co6WIH Ygy7bs+yAiozFYRvr2xo25vvzERqXaAhjtHi42Yv2ABItGG8+WOQNpZ3W9seIpX86Aik Cpaw== X-Gm-Message-State: AOAM530CzlEqSxC0g+TqB7+as2i5q4KSyZxkxvizzAqLSqRVhul1VRpB 70wcVdxRgrfeUNNSIsg1ZCaLtXXkapdLsi+kb0Y= X-Google-Smtp-Source: ABdhPJxcgpkjyb1jD7G3yKubFEG/BUu91rZEanTZL99fRJf9XRT4HlXjbJWs/s3cGBXgeP0HlhJ6nsjncfJ2tThREPs= X-Received: by 2002:aca:d505:: with SMTP id m5mr5889860oig.5.1627020723344; Thu, 22 Jul 2021 23:12:03 -0700 (PDT) MIME-Version: 1.0 References: <20210723051626.18364-1-guang.zeng@intel.com> In-Reply-To: <20210723051626.18364-1-guang.zeng@intel.com> From: Wanpeng Li Date: Fri, 23 Jul 2021 14:11:52 +0800 Message-ID: Subject: Re: [PATCH v2 0/6] IPI virtualization support for VM To: Zeng Guang Cc: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm , Dave Hansen , Tony Luck , Kan Liang , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Kim Phillips , Jarkko Sakkinen , Jethro Beekman , Kai Huang , "the arch/x86 maintainers" , LKML , Robert Hu , Gao Chao Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 23 Jul 2021 at 13:41, Zeng Guang wrote: > > Current IPI process in guest VM will virtualize the writing to interrupt > command register(ICR) of the local APIC which will cause VM-exit anyway > on source vCPU. Frequent VM-exit could induce much overhead accumulated > if running IPI intensive task. > > IPI virtualization as a new VT-x feature targets to eliminate VM-exits > when issuing IPI on source vCPU. It introduces a new VM-execution > control - "IPI virtualization"(bit4) in the tertiary processor-based > VM-exection controls and a new data structure - "PID-pointer table > address" and "Last PID-pointer index" referenced by the VMCS. When "IPI > virtualization" is enabled, processor emulateds following kind of writes > to APIC registers that would send IPIs, moreover without causing VM-exits. > - Memory-mapped ICR writes > - MSR-mapped ICR writes > - SENDUIPI execution > > This patch series implement IPI virtualization support in KVM. > > Patches 1-4 add tertiary processor-based VM-execution support > framework. > > Patch 5 implement interrupt dispatch support in x2APIC mode with > APIC-write VM exit. In previous platform, no CPU would produce > APIC-write VM exit with exit qulification 300H when the "virtual x2APIC > mode" VM-execution control was 1. > > Patch 6 implement IPI virtualization related function including > feature enabling through tertiary processor-based VM-execution in > various scenario of VMCS configuration, PID table setup in vCPU creation > and vCPU block consideration. > > Document for IPI virtualization is now available at the latest "Intel > Architecture Instruction Set Extensions Programming Reference". > > Document Link: > https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html > > We did experiment to measure average time sending IPI from source vCPU > to the target vCPU completing the IPI handling by kvm unittest w/ and > w/o IPI virtualization. When IPI virtualizatin enabled, it will reduce > 22.21% and 15.98% cycles consuming in xAPIC mode and x2APIC mode > respectly. > > KMV unittest:vmexit/ipi, 2 vCPU, AP was modified to run in idle loop > instead of halt to ensure no VM exit impact on target vCPU. > > Cycles of IPI > xAPIC mode x2APIC mode > test w/o IPIv w/ IPIv w/o IPIv w/ IPIv > 1 6106 4816 4265 3768 > 2 6244 4656 4404 3546 > 3 6165 4658 4233 3474 > 4 5992 4710 4363 3430 > 5 6083 4741 4215 3551 > 6 6238 4904 4304 3547 > 7 6164 4617 4263 3709 > 8 5984 4763 4518 3779 > 9 5931 4712 4645 3667 > 10 5955 4530 4332 3724 > 11 5897 4673 4283 3569 > 12 6140 4794 4178 3598 > 13 6183 4728 4363 3628 > 14 5991 4994 4509 3842 > 15 5866 4665 4520 3739 > 16 6032 4654 4229 3701 > 17 6050 4653 4185 3726 > 18 6004 4792 4319 3746 > 19 5961 4626 4196 3392 > 20 6194 4576 4433 3760 > > Average cycles 6059 4713.1 4337.85 3644.8 > %Reduction -22.21% -15.98% > > -------------------------------------- > IPI microbenchmark: > (https://lore.kernel.org/kvm/20171219085010.4081-1-ynorov@caviumnetworks.com) > > 2 vCPUs, 1:1 pin vCPU to pCPU, guest VM runs with idle=poll, x2APIC mode Improve the performance for unicast ipi is as expected, however, I wonder whether the broadcast performance is worse than PV IPIs/Thomas's IPI shorthands(IPI shorthands are supported by upstream linux apic/x2apic driver). The hardware acceleration is not always outstanding on AMD(https://lore.kernel.org/kvm/CANRm+Cx597FNRUCyVz1D=B6Vs2GX3Sw57X7Muk+yMpi_hb+v1w@mail.gmail.com/), how about your Intel guys? Please try a big VM at least 96 vCPUs as below or more bigger. > > Result with IPIv enabled: > > Dry-run: 0, 272798 ns > Self-IPI: 5094123, 11114037 ns > Normal IPI: 131697087, 173321200 ns > Broadcast IPI: 0, 155649075 ns > Broadcast lock: 0, 161518031 ns > > Result with IPIv disabled: > > Dry-run: 0, 272766 ns > Self-IPI: 5091788, 11123699 ns > Normal IPI: 145215772, 174558920 ns > Broadcast IPI: 0, 175785384 ns > Broadcast lock: 0, 149076195 ns > > > As IPIv can benefit unicast IPI to other CPU, Noraml IPI test case gain > about 9.73% time saving on average out of 15 test runs when IPIv is > enabled. > > w/o IPIv w/ IPIv > Normal IPI: 145944306.6 ns 131742993.1 ns > %Reduction -9.73% > > -------------------------------------- > hackbench: > > 8 vCPUs, guest VM free run, x2APIC mode > ./hackbench -p -l 100000 > > w/o IPIv w/ IPIv > Time: 91.887 74.605 > %Reduction: -18.808% > > 96 vCPUs, guest VM free run, x2APIC mode > ./hackbench -p -l 1000000 > > w/o IPIv w/ IPIv > Time: 287.504 235.185 > %Reduction: -18.198% Good to know this. Wanpeng