From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754565AbXKSO2S (ORCPT ); Mon, 19 Nov 2007 09:28:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753070AbXKSO2I (ORCPT ); Mon, 19 Nov 2007 09:28:08 -0500 Received: from tomts43-srv.bellnexxia.net ([209.226.175.110]:58444 "EHLO tomts43-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753057AbXKSO2H (ORCPT ); Mon, 19 Nov 2007 09:28:07 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ah4FAHssQUdMROHU/2dsb2JhbACBWA Date: Mon, 19 Nov 2007 09:28:03 -0500 From: Mathieu Desnoyers To: Rusty Russell Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Andi Kleen , "H. Peter Anvin" , Chuck Ebbert , Christoph Hellwig , Jeremy Fitzhardinge , Ingo Molnar , Thomas Gleixner Subject: Re: [patch 5/8] Immediate Values - x86 Optimization (simplified) Message-ID: <20071119142803.GA19301@Krystal> References: <20071113185800.436425570@polymtl.ca> <200711152206.07519.rusty@rustcorp.com.au> <20071116140334.GA14930@Krystal> <200711191011.18634.rusty@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <200711191011.18634.rusty@rustcorp.com.au> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 08:12:04 up 15 days, 18:17, 3 users, load average: 0.74, 0.78, 1.01 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Rusty Russell (rusty@rustcorp.com.au) wrote: > On Saturday 17 November 2007 01:03:35 Mathieu Desnoyers wrote: > > x86 optimization of the immediate values which uses a movl with code > > patching to set/unset the value used to populate the register used as > > variable source. > > Since immediate values are by definition an optimization, I think it makes > sense to insist they be 1, 2, 4 or 8 bytes. A BUILD_BUG_ON() in the right > place should ensure this (probably in generic code rather than x86). > sure, > > =================================================================== > > --- linux-2.6-lttng.orig/arch/x86/kernel/traps_32.c > > I don't think you need any modification to this file now. > yep, > > + * Create the instruction in a discarded section to calculate its size. This is > > + * how we can align the beginning of the instruction on an address that will > > + * permit atomic modificatino of the immediate value without knowing the size of > > + * the opcode used by the compiler. The operand size is known in advance. > > + */ > > This alignment is also now unnecessary. > right, > > +++ linux-2.6-lttng/arch/x86/kernel/immediate.c 2007-11-16 > > 08:56:22.000000000 -0500 @@ -0,0 +1,143 @@ > > +/* > > + * Immediate Value - x86 architecture specific code. > > This is now almost entirely generic code, but I suppose we can let the next > architecture hoist it out. > I'll move it to kernel/immediate.c. We can therefore remove the powerpc immediate.c as well. > > +/** > > + * arch_immediate_update_early - update one immediate value at boot time > > + * @immediate: pointer of type const struct __immediate to update > > + * > > + * Update one immediate value at boot time. > > + */ > > +void arch_immediate_update_early(const struct __immediate *immediate) > > I think it would be easier to just fast-path the num_online_cpus == 1 case, > even if you want to keep this "update_early" interface. > Nope, that could lead to problems. I call core_immediate_update() _very_ early, before boot_cpu_init() is called. Therefore, cpu_online_map is not set yet. I am not sure the benefit of using num_online_cpus outweights the added fragility wrt other boot process initializations. > But I like your IPI algorithm: very tight. > Thanks. Many thanks for the review, I'll repost the patchset for comments. Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68