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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 4D030C3F2D1 for ; Fri, 6 Mar 2020 02:27:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20F5D206D7 for ; Fri, 6 Mar 2020 02:27:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="fNnR7DkU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726650AbgCFC1j (ORCPT ); Thu, 5 Mar 2020 21:27:39 -0500 Received: from mail-oi1-f194.google.com ([209.85.167.194]:37632 "EHLO mail-oi1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726191AbgCFC1j (ORCPT ); Thu, 5 Mar 2020 21:27:39 -0500 Received: by mail-oi1-f194.google.com with SMTP id q65so1074607oif.4; Thu, 05 Mar 2020 18:27:37 -0800 (PST) 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=PVjfSA1+DzW6af2AGGfVssQK6CSOVfSVNfBqjqDJ0FU=; b=fNnR7DkUUzgPGdh4S3Yl0ximE4vfPB6PiH1oembl/1Cnm11boeicDm+STbdDS4POcw JQS6xkC5lTv90kwtU6+1WC008Ztgywud4EwVDEbkhL/tWlBvIlh+5jA143TztwYG3f/u lUVk34XCWMms/yY+gm1HNCpqg4DFSf/In6BrbV+eozr0aB8VYvcsK2QdhMal40kyF5H9 FyzOfxQXKz2JQWvE7E6nNPDMLKulFTVLbFm5Xdpbawij97Ms+5f1DY5Omkk8UyZVa6Jv gyOpjDBOsBQT9+IRCLtVu4Y8QMNalL9BMo2JY1Kdi89TK75ymZSxxORyrNvgpzbuxtjn Nzow== 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=PVjfSA1+DzW6af2AGGfVssQK6CSOVfSVNfBqjqDJ0FU=; b=JE/ES2gf9ogQv3IB6zvGGt76UhfEJGVwskM/pflIbTRD1RIjeGUX1gEuYRjRnKtb76 SJQwC1fOllPnHyYHIIB5+gTdGaakSL670iY76Io/txb6McwI5HlSHBqrmsfb83U8Tv3Q pSDlndBkfyPARDDkIWqQcNdsauujRl0rtt9V7Q5Y5fWUBGrEcAPZ6LiGLZnRat4b+G0I HwOWcVAcEt82BFGMUUc0Z9uvHEioyXtTYhv5XIgGe0EBWt4C0sUI8vYq9bMlvG8Nj/3S tYT4KB75Eop8fxNbN4FeZkjZHFzgR14S/yMikTvKQoLPRksaWG1IdayujeFybGCMety3 8JIg== X-Gm-Message-State: ANhLgQ1YWjRWOb7xMEigPxHj+cahb9x2/kS4jerxSrx2bl4hDv6MUhOM q+lHkR0BX8bGb0F8+f2K9I6ooXYWGb2nPuOlUIY= X-Google-Smtp-Source: ADFU+vuciy87JcOO9oRPhhmjgf127Yf5g7ICoTrpeUd2Qyrvb52OLwc7q2zNmTJo6h826ewwvjuJh/dsyo0pvQSC9tY= X-Received: by 2002:aca:5f09:: with SMTP id t9mr1108587oib.5.1583461657164; Thu, 05 Mar 2020 18:27:37 -0800 (PST) MIME-Version: 1.0 References: <4e9d847ea5d54e4fa83f3bb910242e16@huawei.com> In-Reply-To: <4e9d847ea5d54e4fa83f3bb910242e16@huawei.com> From: Wanpeng Li Date: Fri, 6 Mar 2020 10:27:26 +0800 Message-ID: Subject: Re: [PATCH] KVM: x86: small optimization for is_mtrr_mask calculation To: linmiaohe Cc: "hpa@zytor.com" , Paolo Bonzini , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "rkrcmar@redhat.com" , "sean.j.christopherson@intel.com" , "vkuznets@redhat.com" , "jmattson@google.com" , "joro@8bytes.org" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 6 Mar 2020 at 10:23, linmiaohe wrote: > > hpa@zytor.com wrote: > >>On March 5, 2020 6:05:40 PM PST, linmiaohe wrote: > >>Hi, > >>Paolo Bonzini wrote: > >>Many thanks for suggestion. What do you mean is like this ? > >> > >> index = (msr - 0x200) >> 1; > >> is_mtrr_mask = msr & 1; > >> > >>Thanks again. > > > >You realize that the compiler will probably produce exactly the same code, right? As such, it is about making the code easy for the human reader. > > > >Even if it didn't, this code is as far from performance critical as one can possibly get. > > Yep, it looks gain little. Thanks. Please post the performance number when you mention optimize XXX later. Wanpeng