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 0FD01C433DB 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 C9F7022262 for ; Mon, 28 Dec 2020 23:29:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728537AbgL1X3U (ORCPT ); Mon, 28 Dec 2020 18:29:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32942 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727731AbgL1X3T (ORCPT ); Mon, 28 Dec 2020 18:29:19 -0500 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 764D8C0613D6 for ; Mon, 28 Dec 2020 15:28:39 -0800 (PST) Received: by mail-pg1-x529.google.com with SMTP id e2so8195180pgi.5 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=uYjAMX7DWavcZzgUO9mMA2BFr9Y0KAI7X2cShJjpAq/XalM+NCjg+ag/7DzmZf0p+d +wPrrjQZSoiAUzhoxAfCdnZBqcQN1FTXPFKfgIYV8hlICzcmJjYLRsJmfzdPhap+kCTc nQREJ9Arq9BM8glupIi9VNYV2GIZs6vYmvdL7kl+fpmakGwO8UiNzhOlPNy6XYLxHDQn pSdKGAaDYTtXUP1oAMghJ7yD1P/+Brhh7H/jjWp7r0H8GGHI7WdPqoq/dCN0820NT4RR dlSKNFCP9HmiLXZ1qUgzRzoxO3FiBHV8j91U5RNRLCPR7SakwpDuKiM2+p7xnPOPDRoC esAQ== X-Gm-Message-State: AOAM530+pos5FWcgtCHhHvU+fLdjSwNWXRfWTIvtQmjRXKPl/WlQ7MAZ hJVPub7hN9jiYNOMeE4xPfA7jg== 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: linux-kernel@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.