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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,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 B1BBCC5DF9E for ; Thu, 29 Oct 2020 17:20:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D49820759 for ; Thu, 29 Oct 2020 17:20:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="kCwHtNb0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727123AbgJ2RUw (ORCPT ); Thu, 29 Oct 2020 13:20:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbgJ2RUv (ORCPT ); Thu, 29 Oct 2020 13:20:51 -0400 Received: from mail-qk1-x72e.google.com (mail-qk1-x72e.google.com [IPv6:2607:f8b0:4864:20::72e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B93A9C0613CF; Thu, 29 Oct 2020 10:20:51 -0700 (PDT) Received: by mail-qk1-x72e.google.com with SMTP id z6so2603644qkz.4; Thu, 29 Oct 2020 10:20:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=bgET2vKXyCysvHtuVXHC8x2bsoHr9I9pVPGZuJ2I2ok=; b=kCwHtNb0aDqVERdhKoxZMhicLRZ2QR3PolGpflI38e1AZzBFPmngVCvkULn12HaIpd xNZsE0KTf8SFsTeciNeDfLB2b8eo7aWwi+oWAp/jGZANfyHEmSTDAiXW3x245FjthbK+ cNyymvnYwa4RgDaOm832TsIoNGN5VteNRutW9xIM3LOXzwfrz3rFIbB2qhaahGSK3KWZ rcjSGv+Lrv3xXtp7IhxItj2ThU4R1TxkB1brB4zm0qayhFjR52RmdpupiWUa8/437Az6 Z5hmy1fEbRMjrq5fMw2J1qv+hvc2qIZX/q2dYGHrv1hoTM8Kgy/UG1ajYtjFlzWenf9F /BdA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:date:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=bgET2vKXyCysvHtuVXHC8x2bsoHr9I9pVPGZuJ2I2ok=; b=PuClkGl0pB78zr0m2LspFo1DPMrsifWAoPRU58VwsHOmXNCdg6ZXIrGwVyBsIK2Sbf jNJvc3xbrUnvHTd3HLJARpWjlK0N9deC/a8H6oipyMPtlLzetTMk3BIsPckJSh3GY/Wo 49+oY0x4amY489fIhsM5RAPnDPF2UjwJagF0igwBbh+qZCb4Ez8k3+843+6fX5SkDjXt AMeRsiNR/qxTlLaj3eDrprQmfZySfSF+Z8SoacFWq6BhzcrQFNi1l8uR3KRN01uPQP8i jYYMm4jcV/LWLTy5oTd78YETXZbkvQV4uoWYHObwdqVGUDGuvVCnrgWAYlr9GayJ2N7M wuew== X-Gm-Message-State: AOAM533Kz/RR9Ng5oN4cJKqraFrzB+p9Gnem/CmMUaIf/ksolQhD+LMj pQNUxed42kiccxNpM9KAF64= X-Google-Smtp-Source: ABdhPJxpj2lHqddfkMCdJsg7kjoxJdmwW/wIVKjCyqCU3W25AK0ciYoXUlV7HQMe/OgzwbBLEfxGlQ== X-Received: by 2002:a05:620a:130a:: with SMTP id o10mr4612780qkj.63.1603992050890; Thu, 29 Oct 2020 10:20:50 -0700 (PDT) Received: from rani.riverdale.lan ([2001:470:1f07:5f3::b55f]) by smtp.gmail.com with ESMTPSA id m33sm1432097qtb.65.2020.10.29.10.20.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Oct 2020 10:20:50 -0700 (PDT) Sender: Arvind Sankar From: Arvind Sankar X-Google-Original-From: Arvind Sankar Date: Thu, 29 Oct 2020 13:20:48 -0400 To: Paolo Bonzini Cc: Arvind Sankar , David Laight , 'Arnd Bergmann' , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "x86@kernel.org" , Arnd Bergmann , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , "H. Peter Anvin" , "Rafael J. Wysocki" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "platform-driver-x86@vger.kernel.org" , "xen-devel@lists.xenproject.org" , "iommu@lists.linux-foundation.org" Subject: Re: [PATCH] [v2] x86: apic: avoid -Wshadow warning in header Message-ID: <20201029172048.GA2571425@rani.riverdale.lan> References: <20201028212417.3715575-1-arnd@kernel.org> <38b11ed3fec64ebd82d6a92834a4bebe@AcuMS.aculab.com> <20201029165611.GA2557691@rani.riverdale.lan> <93180c2d-268c-3c33-7c54-4221dfe0d7ad@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <93180c2d-268c-3c33-7c54-4221dfe0d7ad@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 29, 2020 at 05:59:54PM +0100, Paolo Bonzini wrote: > On 29/10/20 17:56, Arvind Sankar wrote: > >> For those two just add: > >> struct apic *apic = x86_system_apic; > >> before all the assignments. > >> Less churn and much better code. > >> > > Why would it be better code? > > > > I think he means the compiler produces better code, because it won't > read the global variable repeatedly. Not sure if that's true,(*) but I > think I do prefer that version if Arnd wants to do that tweak. > > Paolo > > (*) if it is, it might also be due to Linux using -fno-strict-aliasing > Nope, it doesn't read it multiple times. I guess it still assumes that apic isn't in the middle of what it points to: it would reload the address if the first element of *apic was modified, but doesn't for other elements. Interesting.