From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753299AbXLMWlU (ORCPT ); Thu, 13 Dec 2007 17:41:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755492AbXLMWlK (ORCPT ); Thu, 13 Dec 2007 17:41:10 -0500 Received: from mailout.stusta.mhn.de ([141.84.69.5]:45638 "EHLO mailhub.stusta.mhn.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752826AbXLMWlJ (ORCPT ); Thu, 13 Dec 2007 17:41:09 -0500 Date: Thu, 13 Dec 2007 23:41:11 +0100 From: Adrian Bunk To: Andi Kleen Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: RFC: remove __read_mostly Message-ID: <20071213224111.GI21616@stusta.de> References: <20071213222044.GH21616@stusta.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 13, 2007 at 11:29:08PM +0100, Andi Kleen wrote: > Adrian Bunk writes: > > > > -rwxrwxr-x 1 bunk bunk 46607243 2007-12-13 19:50 vmlinux.old > > -rwxrwxr-x 1 bunk bunk 46598691 2007-12-13 21:55 vmlinux > > File sizes are useless -- check size output. text data bss dec hex filename 29268488 3697961 5222400 38188849 246b731 vmlinux.old 29268435 3685565 5228784 38192784 246c690 vmlinux > > It's not a surprise that the kernel can become bigger when __read_mostly > > gets used, especially in cases where __read_mostly prevents gcc > > optimizations. > > What optimizations do you think it prevents? I don't think it > should change the gcc generated code at all; the only difference > should be to the linker. What I have seen recently was a static variable marked __read_mostly being read-only with some CONFIG_DEBUG_FOO=n. With __read_mostly gcc feeled obliged to emit a variable. Without __read_mostly, gcc optimized the variable away. > -Andi cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed