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 7F698C636CA for ; Fri, 16 Jul 2021 09:25:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66E61613D4 for ; Fri, 16 Jul 2021 09:25:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233375AbhGPJ2T (ORCPT ); Fri, 16 Jul 2021 05:28:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231354AbhGPJ2Q (ORCPT ); Fri, 16 Jul 2021 05:28:16 -0400 Received: from mail-oi1-x233.google.com (mail-oi1-x233.google.com [IPv6:2607:f8b0:4864:20::233]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F119BC06175F; Fri, 16 Jul 2021 02:25:19 -0700 (PDT) Received: by mail-oi1-x233.google.com with SMTP id u15so10186692oiw.3; Fri, 16 Jul 2021 02:25:19 -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=M3L6N/isUtLMNrxa1XCwVdqbDJYk3wmwipYc7UHIg30=; b=r4+zxL8Ly1S8l0ZTRBbHhjuykg+E/jFwukwFh3ZLskQKJmd22UtiHt9e8Vrc4B/r1E StnSypkfyxFZx/dILMKWn0jGTvuzX5X/Vf8Np9xiQsE0TiMRPZFjQisx7QQXlZL9Duk/ KXwqG2D4cf5WMWD+8ks9BTvFkTqg0X34U5ZTbw8Pmmky5S+tRtvNJJKJN9+yatdb5s0i 4nnTnwrvJKghJ4z3ARRSdRv2gp5YKVngkA5lzcrK65yF6Zn1sl+8nT+i+0RdxoKKRRKQ JCIK93oHSE7ncCgx6BlwZp09fjFbXlB8kcmD0zPR8fQOKuxkxHIZg0VXPvJKTCVY8TV+ 9MDQ== 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=M3L6N/isUtLMNrxa1XCwVdqbDJYk3wmwipYc7UHIg30=; b=XoscfH+ptbr5QKOb/JwR4JDr/VM7Yu4Pp0qiEAk+TIfaYVjtKnQbwsF01JIw9cB7dU YrKIeaotCRZiJPK+FQcswO2CF1nCN9sU0CFoo5UiKCQeyBEzIX7sTaPJmZfZb5SSudyq a4BK4VtRu7x/sAGG7zGgKCsw4VeUASJ6QxRrqTQ0SV/9IrfAHD+p+hvN4jXSMhgou/47 z3s9Etw0GrdvVteds50YeOb3Z9rjYs/CpkIZC3vcIkRPligckX3c1Zo5S8V9jGz9g35j GHSTcP23gFlDBPlN9WKPREGsnVwxkhwtLzEPpRYH9JBO522OQvr2WRJj8uPZc3QWYimA Y/uA== X-Gm-Message-State: AOAM531v5+y2yLT5F4Q5coudE1Njy9YmtFU9TOT7jN5b6vR8RS+CrVHR gighozRKBDIo+inkHl2oyFK7WpLNBPQeTSZ6ee4= X-Google-Smtp-Source: ABdhPJxHyb8ANuJhmrB3GrlnpY3IjWqx4f3k/5MpMwr2A8uB+jRVB/RRadAnxqsI07492YshjiCdsR22hzW+eMENJfA= X-Received: by 2002:aca:1017:: with SMTP id 23mr1121001oiq.141.1626427519435; Fri, 16 Jul 2021 02:25:19 -0700 (PDT) MIME-Version: 1.0 References: <20210716064808.14757-1-guang.zeng@intel.com> In-Reply-To: <20210716064808.14757-1-guang.zeng@intel.com> From: Wanpeng Li Date: Fri, 16 Jul 2021 17:25:08 +0800 Message-ID: Subject: Re: [PATCH 0/5] 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, 16 Jul 2021 at 15:14, 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 1-3 add tertiary processor-based VM-execution support > framework. > > Patch 4 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 5 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 comsuming in xAPIC mode and x2APIC mode > respectly. > > KMV unittest:vmexit/ipi, 2 vCPU, AP runs without 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% Commit a9ab13ff6e (KVM: X86: Improve latency for single target IPI fastpath) mentioned that the whole ipi fastpath feature reduces the latency from 4238 to 3293 around 22.3% on SKX server, why your IPIv hardware acceleration is worse than software emulation? In addition, please post the IPI microbenchmark score w/ and w/o the patchset.(https://lore.kernel.org/kvm/20171219085010.4081-1-ynorov@caviumnetworks.com), I found that the hardware acceleration is not always outstanding. https://lore.kernel.org/kvm/CANRm+Cx597FNRUCyVz1D=B6Vs2GX3Sw57X7Muk+yMpi_hb+v1w@mail.gmail.com Wanpeng