Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932545Ab1CINyx (ORCPT ); Wed, 9 Mar 2011 08:54:53 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:56159 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932208Ab1CINyw convert rfc822-to-8bit (ORCPT ); Wed, 9 Mar 2011 08:54:52 -0500 Subject: Re: [BUG] rebuild_sched_domains considered dangerous From: Peter Zijlstra To: Martin Schwidefsky Cc: Benjamin Herrenschmidt , "linux-kernel@vger.kernel.org" , linuxppc-dev , Jesse Larrew In-Reply-To: <20110309144636.3f0899d1@mschwide.boeblingen.de.ibm.com> References: <1299639487.22236.256.camel@pasglop> <1299665998.2308.2753.camel@twins> <1299670429.2308.2834.camel@twins> <20110309141548.722e4f56@mschwide.boeblingen.de.ibm.com> <1299676769.2308.2944.camel@twins> <20110309143152.3cc6c191@mschwide.boeblingen.de.ibm.com> <1299677636.2308.2960.camel@twins> <20110309144636.3f0899d1@mschwide.boeblingen.de.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Wed, 09 Mar 2011 14:54:39 +0100 Message-ID: <1299678879.2308.2987.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1488 Lines: 29 On Wed, 2011-03-09 at 14:46 +0100, Martin Schwidefsky wrote: > On Wed, 09 Mar 2011 14:33:56 +0100 > Peter Zijlstra wrote: > > > On Wed, 2011-03-09 at 14:31 +0100, Martin Schwidefsky wrote: > > > > But if you don't also update the cpu->node memory mappings (which I > > > > think it near impossible) what good is it to change the scheduler > > > > topology? > > > > > > The memory for the different LPARs is striped over all nodes (or books as we > > > call them). We heavily rely on the large shared cache between the books to hide > > > the different memory access latencies. > > > > Right, so effectively you don't have NUMA due to that striping. So why > > then change the CPU topology? Simply create a topology without NUMA and > > keep it static, that accurately reflects the memory topology. > > Well the CPU topology can change due to different grouping of logical CPUs > dependent on which LPARs are activated. And we effectively do not have a > memory topology, only CPU. Its basically all about caches, we want to > reflect the distance between CPUs over the up to 4 cache levels. Right, so I consider caches to be part of the memory topology, anyway, if this all is very rare then yeah, that works out. -- 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/