From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756195AbXLaQT7 (ORCPT ); Mon, 31 Dec 2007 11:19:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751599AbXLaQTw (ORCPT ); Mon, 31 Dec 2007 11:19:52 -0500 Received: from relay2.sgi.com ([192.48.171.30]:59780 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751822AbXLaQTv (ORCPT ); Mon, 31 Dec 2007 11:19:51 -0500 Message-ID: <477916A9.6030001@sgi.com> Date: Mon, 31 Dec 2007 08:19:53 -0800 From: Mike Travis User-Agent: Thunderbird 2.0.0.6 (X11/20070801) MIME-Version: 1.0 To: Andi Kleen CC: Andrew Morton , Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rusty Russell , tglx@linutronix.de, mingo@redhat.com Subject: Re: [PATCH 05/10] x86_64: Use generic percpu References: <20071228001046.854702000@sgi.com> <200712281354.52453.ak@suse.de> <47757311.5050503@sgi.com> <200712290255.40233.ak@suse.de> In-Reply-To: <200712290255.40233.ak@suse.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andi Kleen wrote: > On Friday 28 December 2007 23:05:05 Mike Travis wrote: >> Andi Kleen wrote: >>> On Friday 28 December 2007 01:10:51 travis@sgi.com wrote: >>>> x86_64 provides an optimized way to determine the local per cpu area >>>> offset through the pda and determines the base by accessing a remote >>>> pda. >>> And? The rationale for this patch seems to be incomplete. >>> >>> As far as I can figure out you're replacing an optimized percpu >>> implementation which a dumber generic one. Which needs >>> at least some description why. >> The specific intent for the next wave of changes coming are to reduce > [...] That should be in the changelog of the patch. > > Anyways the difference between the x86 percpu.h and the generic one is > that x86-64 uses a short cut through the PDA to get the current cpu > offset for the current CPU case. The generic one goes through > smp_processor_id()->array reference instead. > > I would request that this optimization is not being removed > without suitable replacement in the same patchkit. > > -Andi I'll take a closer look at this, but it may have to wait until Christoph is back this Wednesday. Thanks, Mike