Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933115AbXH0Ubl (ORCPT ); Mon, 27 Aug 2007 16:31:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762955AbXH0U0N (ORCPT ); Mon, 27 Aug 2007 16:26:13 -0400 Received: from netops-testserver-3-out.sgi.com ([192.48.171.28]:38450 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1763102AbXH0U0L (ORCPT ); Mon, 27 Aug 2007 16:26:11 -0400 Date: Mon, 27 Aug 2007 13:26:11 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Mathieu Desnoyers cc: Peter Zijlstra , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, mingo@redhat.com Subject: Re: [PATCH] SLUB use cmpxchg_local In-Reply-To: <20070827202203.GB5653@Krystal> Message-ID: References: <20070820204126.GA22507@Krystal> <20070820212922.GA27011@Krystal> <20070820215413.GA28452@Krystal> <20070821173849.GA8360@Krystal> <1188197539.6114.426.camel@twins> <20070827202203.GB5653@Krystal> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1274 Lines: 29 On Mon, 27 Aug 2007, Mathieu Desnoyers wrote: > * 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) ? Not sure exactly what you are getting at? This would mean running __alloc_pages tied to one processor even though waiting is possible? - 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/