From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964829AbWAMPTg (ORCPT ); Fri, 13 Jan 2006 10:19:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964965AbWAMPTg (ORCPT ); Fri, 13 Jan 2006 10:19:36 -0500 Received: from mailout.stusta.mhn.de ([141.84.69.5]:18956 "HELO mailout.stusta.mhn.de") by vger.kernel.org with SMTP id S964829AbWAMPTf (ORCPT ); Fri, 13 Jan 2006 10:19:35 -0500 Date: Fri, 13 Jan 2006 16:19:34 +0100 From: Adrian Bunk To: Andrew Morton Cc: "Bryan O'Sullivan" , hch@infradead.org, rdreier@cisco.com, sam@ravnborg.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1 of 3] Introduce __raw_memcpy_toio32 Message-ID: <20060113151934.GO29663@stusta.de> References: <20060110011844.7a4a1f90.akpm@osdl.org> <1136909276.32183.28.camel@serpentine.pathscale.com> <20060110170722.GA3187@infradead.org> <1136915386.6294.8.camel@serpentine.pathscale.com> <20060110175131.GA5235@infradead.org> <1136915714.6294.10.camel@serpentine.pathscale.com> <20060110140557.41e85f7d.akpm@osdl.org> <1136932162.6294.31.camel@serpentine.pathscale.com> <20060110153257.1aac5370.akpm@osdl.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060110153257.1aac5370.akpm@osdl.org> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 10, 2006 at 03:32:57PM -0800, Andrew Morton wrote: > "Bryan O'Sullivan" wrote: > > > > On Tue, 2006-01-10 at 14:05 -0800, Andrew Morton wrote: > > > > > It's kinda fun playing Brian along like this ;) > > > > A regular barrel of monkeys, indeed... > > > > > One option is to just stick the thing in an existing lib/ or kernel/ file > > > and mark it __attribute__((weak)). That way architectures can override it > > > for free with no ifdefs, no Makefile trickery, no Kconfig trickery, etc. > > > > I'm easy. Would you prefer to take that, or the Kconfig-trickery-based > > patch series I already posted earlier? > > > > Unless someone can think of a problem with attribute(weak), I think you'll > find that it's the simplest-by-far solution. __attribute__((weak)) can turn compile error into runtime errors - you won't notice at compile time if it was forgotten to compile the non-weak version into the kernel (e.g. due to a typo in the Makefile). Patch 05/17 from the 2.6.15.1 patchset contains a fix for such a bug present in 2.6.15. A variation of this problem can occur in cases like __raw_memcpy_toio32 if it was forgotten to compile the non-weak version into the kernel and the kernel therefore uses the non-optimized version. That's not fatal, but it might take years until someone notices that there might be a few percent of performance missing. 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