From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750893AbVLIBw1 (ORCPT ); Thu, 8 Dec 2005 20:52:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750901AbVLIBw0 (ORCPT ); Thu, 8 Dec 2005 20:52:26 -0500 Received: from waste.org ([64.81.244.121]:21385 "EHLO waste.org") by vger.kernel.org with ESMTP id S1750885AbVLIBw0 (ORCPT ); Thu, 8 Dec 2005 20:52:26 -0500 Date: Thu, 8 Dec 2005 17:46:59 -0800 From: Matt Mackall To: Ingo Molnar Cc: Jesper Juhl , Linux Kernel Mailing List , Andrew Morton Subject: Re: [RFC][PATCH] Reduce number of pointer derefs in various files (kernel/exit.c used as example) Message-ID: <20051209014658.GA11856@waste.org> References: <200512062302.06933.jesper.juhl@gmail.com> <20051206221528.GA12358@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20051206221528.GA12358@elte.hu> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 06, 2005 at 11:15:28PM +0100, Ingo Molnar wrote: > > * Jesper Juhl wrote: > > > Ohh, and before I forget, besides the fact that this should speed > > things up a little bit it also has the added benefit of reducing the > > size of the generated code. The original kernel/exit.o file was 19604 > > bytes in size, the patched one is 19508 bytes in size. > > nice. Just to underline your point, on x86, with gcc 4.0.2, i'm getting > this with your patch: > > text data bss dec hex filename > 11077 0 0 11077 2b45 exit.o.orig > 10997 0 0 10997 2af5 exit.o > > so 80 bytes shaved off. I think such patches also increase readability. Readability improved: good. 37 lines of patch for 80-100 bytes saved: not so good. So while this is a good style direction, I don't think it's worth the churn. And unlike kzalloc and the like, this particular optimization is perfectly doable by a compiler. So I'd rather wait for the compiler to get smarter than change code for such modest improvements. FYI, much other low-hanging size-reduction fruit remains in the kernel. Lots of it in the form of duplicate code. -- Mathematics is the supreme nostalgia of our time.