From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755168AbXL2Bzz (ORCPT ); Fri, 28 Dec 2007 20:55:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753399AbXL2Bzs (ORCPT ); Fri, 28 Dec 2007 20:55:48 -0500 Received: from mail.suse.de ([195.135.220.2]:47921 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753007AbXL2Bzr (ORCPT ); Fri, 28 Dec 2007 20:55:47 -0500 From: Andi Kleen Organization: SUSE Linux Products GmbH, Nuernberg, GF: Markus Rex, HRB 16746 (AG Nuernberg) To: Mike Travis Subject: Re: [PATCH 05/10] x86_64: Use generic percpu Date: Sat, 29 Dec 2007 02:55:39 +0100 User-Agent: KMail/1.9.6 Cc: Andrew Morton , Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rusty Russell , tglx@linutronix.de, mingo@redhat.com References: <20071228001046.854702000@sgi.com> <200712281354.52453.ak@suse.de> <47757311.5050503@sgi.com> In-Reply-To: <47757311.5050503@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200712290255.40233.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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