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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 37BFDC433E6 for ; Mon, 28 Dec 2020 23:29:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04551223E8 for ; Mon, 28 Dec 2020 23:29:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728416AbgL1X3U (ORCPT ); Mon, 28 Dec 2020 18:29:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728299AbgL1X3T (ORCPT ); Mon, 28 Dec 2020 18:29:19 -0500 Received: from mail-pg1-x52d.google.com (mail-pg1-x52d.google.com [IPv6:2607:f8b0:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8085DC061793 for ; Mon, 28 Dec 2020 15:28:39 -0800 (PST) Received: by mail-pg1-x52d.google.com with SMTP id p18so8167484pgm.11 for ; Mon, 28 Dec 2020 15:28:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=YHXv2Jc7uDRYfCGmkxwRFDrFxzJk/xjA57oTL7WqPAk=; b=IG4n+U0iEnyjsOCZ36oBibFHyoOloR7t5DabLazjPAe2lmK9D0UpcdC1dKKsDHKU92 +cNGcUFXNXP9hkO3LbUWCr4BRQi8Whnn0wu2z0IWJBCvbK2HBZGFiD4+Zxu0/hukuw4o lk5/1GiSFtPGVEp627njimpcVjMqmpIG/+hZ/x7/ZGthyf687XFMXEzCjJ1BNbefxYu1 Ckfm4sTb/14a3XTyZzu4k0DcHLu3bTxHYOdScTu399djk0ZSL++S4f0s0e8oFurmTvbQ 2KnzVqjqU5gz8irc4zLW+QTUznTF3rr51hGWnCeJsWt/b+EdNpgkby/LqoXldqBS97Se 5wpQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=YHXv2Jc7uDRYfCGmkxwRFDrFxzJk/xjA57oTL7WqPAk=; b=AVD7ceUmIiH5how0Wsm2JWmjMtg69zlR1ROP2P0Dc1mUUnVczHmF2ePnXdY8WWiMCm dYUmSrPz4Pzs6luoYKaTjOcVHNKjwYLKTbd0cB6qXIdgQPNfKIlQS0HnanErApT9w6t6 KYfek3f0nS8hPoVknYYWcOyMaHTCCUFu4wRLA/Kg0nlvDO3A4iv5QevseKTToXB8DxJz 7pVIwQXdXdtD70kJecyQDAkJrexNNfcFlPh+V82iMhj6TOj/O2JKo+spG/7jQDzlGsDL jRC+Xl4znidvQNT9F3miHSt3Bs2Lszyq1dCbxti1lTQ1iqppr28lgyAuhoKzJv6yauT7 D23g== X-Gm-Message-State: AOAM5323ZSc3kSXTqTfoXB34tGIOwIN1fm+mGUrtkxPc6hZEpPW9Xtb8 CEsbDjy4vT5Qz5WRq5uSSQtaRg== X-Google-Smtp-Source: ABdhPJweRY8jL3It79h5jMNDyIgtwp8n/71UFFCLfDWomYceM6Sn3/Me6p1fMh1We7VQeu4ROtUHLA== X-Received: by 2002:a63:44d:: with SMTP id 74mr45370796pge.170.1609198118926; Mon, 28 Dec 2020 15:28:38 -0800 (PST) Received: from google.com ([2620:15c:f:10:1ea0:b8ff:fe73:50f5]) by smtp.gmail.com with ESMTPSA id c199sm38708633pfb.108.2020.12.28.15.28.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Dec 2020 15:28:38 -0800 (PST) Date: Mon, 28 Dec 2020 15:28:31 -0800 From: Sean Christopherson To: Zhimin Feng Cc: zhouyibo@bytedance.com, zhanghaozhong@bytedance.com, Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Frederic Weisbecker , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC: timer passthrough 0/9] Support timer passthrough for VM Message-ID: References: <20201228091559.25745-1-fengzhimin@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201228091559.25745-1-fengzhimin@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Dec 28, 2020, Zhimin Feng wrote: > The main motivation for this patch is to improve the performance of VM. Do you have numbers that show when this improves performance, and by how much? This adds hundreds of cycles of overhead (VMWRITEs, WRMSRs, RDMSRs, etc...) to _every_ VM-Exit roundtrip, and the timer IRQ still incurs a VM-Exit. It's not obvious that this is a net win, and it adds a fair amount of complexity and subtlety, e.g. there are multiple corner cases this gets wrong. I suspect you'll have a tough time getting this reviewed, let alone merged, without hard numbers to justify the complexity and review effort.