Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964869AbWIZW2F (ORCPT ); Tue, 26 Sep 2006 18:28:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964870AbWIZW2E (ORCPT ); Tue, 26 Sep 2006 18:28:04 -0400 Received: from tomts5.bellnexxia.net ([209.226.175.25]:38126 "EHLO tomts5-srv.bellnexxia.net") by vger.kernel.org with ESMTP id S964869AbWIZW2C (ORCPT ); Tue, 26 Sep 2006 18:28:02 -0400 Date: Tue, 26 Sep 2006 18:27:58 -0400 From: Mathieu Desnoyers To: Jeremy Fitzhardinge Cc: Martin Bligh , "Frank Ch. Eigler" , Masami Hiramatsu , prasanna@in.ibm.com, Andrew Morton , Ingo Molnar , Paul Mundt , linux-kernel , Jes Sorensen , Tom Zanussi , Richard J Moore , Michel Dagenais , Christoph Hellwig , Greg Kroah-Hartman , Thomas Gleixner , William Cohen , ltt-dev@shafik.org, systemtap@sources.redhat.com, Alan Cox , Karim Yaghmour , Pavel Machek , Joe Perches , "Randy.Dunlap" , "Jose R. Santos" Subject: Re: [PATCH] Linux Kernel Markers 0.14 for 2.6.17 Message-ID: <20060926222758.GA9668@Krystal> References: <20060926220604.GA30396@Krystal> <4519A58A.7070302@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <4519A58A.7070302@goop.org> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.4.32-grsec (i686) X-Uptime: 18:24:09 up 34 days, 19:32, 3 users, load average: 0.29, 0.25, 0.27 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1564 Lines: 46 * Jeremy Fitzhardinge (jeremy@goop.org) wrote: > Mathieu Desnoyers wrote: > >Hi, > > > >Constructing on Jeremy Fitzhardinge's comments about gcc optimizations, I > >rewrote (once more) the markers mechanism so that the optimized mode does > >not > >jump between two different inline asm. Instead, the optimized version uses > >a > >load immediate (in assembly) that will be used by a test to decide of a > >branch > >(in C). > > > > I should have spelled out my point a bit more. If you've got a flag > you're just testing, couldn't you just do: > > if (__mark_enabled_##name) > (*__mark_func)(...); > > and do without the asms or the section? > Because a supplementary memory read is added on the critical path with a normal flag test. The assembly can provide an immediate value without any need of memory read from the data section. To change the behavior of the program, I just have to change the immediate value in the movb instruction. However, the non-optimized generic version does exactly this : it simply tests a flag loaded from memory. It can be very useful on embedded systems where the code is in read-only memory. Regards, Mathieu OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/