Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759749AbXH0UWU (ORCPT ); Mon, 27 Aug 2007 16:22:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758565AbXH0UWH (ORCPT ); Mon, 27 Aug 2007 16:22:07 -0400 Received: from bc.sympatico.ca ([209.226.175.184]:59397 "EHLO tomts22-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756340AbXH0UWG (ORCPT ); Mon, 27 Aug 2007 16:22:06 -0400 Date: Mon, 27 Aug 2007 16:22:03 -0400 From: Mathieu Desnoyers To: Christoph Lameter Cc: Peter Zijlstra , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, mingo@redhat.com Subject: Re: [PATCH] SLUB use cmpxchg_local Message-ID: <20070827202203.GB5653@Krystal> References: <20070820204126.GA22507@Krystal> <20070820212922.GA27011@Krystal> <20070820215413.GA28452@Krystal> <20070821173849.GA8360@Krystal> <1188197539.6114.426.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 16:20:14 up 28 days, 20:39, 4 users, load average: 0.13, 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: 1223 Lines: 26 * Christoph Lameter (clameter@sgi.com) wrote: > On Mon, 27 Aug 2007, Peter Zijlstra wrote: > > > So, if the fast path can be done with a preempt off, it might be doable > > to suffer the slow path with a per cpu lock like that. > > Sadly the cmpxchg_local requires local per cpu data access. Isnt there > some way to make this less expensive on RT? Acessing cpu local memory is > really good for performance on NUMA since the data is optimally placed and > one can avoid/reduce locking if the process stays tied to the processor. > On the slow path, in slab_new, we already have to reenable interrupts because we can sleep. If we make sure that whenever we return to an irq disable code path we take the current per-cpu data structure again, can we make the preempt-disable/irq-disabled code paths O(1) ? -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP 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/