From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gw1.cosmosbay.com ([86.65.150.130]:53634 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751617AbXKLUPV (ORCPT ); Mon, 12 Nov 2007 15:15:21 -0500 Message-ID: <4738B437.1000204@cosmosbay.com> Date: Mon, 12 Nov 2007 21:14:47 +0100 From: Eric Dumazet MIME-Version: 1.0 Subject: Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu access overhead References: <4738AE04.1030506@cosmosbay.com> <617E1C2C70743745A92448908E030B2A02EDFBB5@scsmsx411.amr.corp.intel.com> In-Reply-To: <617E1C2C70743745A92448908E030B2A02EDFBB5@scsmsx411.amr.corp.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org To: "Luck, Tony" Cc: Christoph Lameter , Herbert Xu , David Miller , akpm@linux-foundation.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, mathieu.desnoyers@polymtl.ca, penberg@cs.helsinki.fi List-ID: Luck, Tony a écrit : >>> Ahh so the need to be able to expand per cpu memory storage on demand >>> is not as critical as we thought. >>> >> Yes, but still desirable for future optimizations. >> >> For example, I do think using a per cpu memory storage on net_device refcnt & >> last_rx could give us some speedups. > > We do want to keep a very tight handle on bloat in per-cpu > allocations. By definition the total allocation is multiplied > by the number of cpus. Only ia64 has outrageous numbers of > cpus in a single system image today ... but the trend in > multi-core chips looks to have a Moore's law arc to it, so > everyone is going to be looking at lots of cpus before long. > I dont think this is a problem. Cpus numbers and ram size are related, even if Moore didnt predicted it; Nobody wants to ship/build a 4096 cpus machine with 256 MB of ram inside. Or call it a GPU and dont expect it to run linux :) 99,9% of linux machines running on earth have less than 8 cpus and less than 1000 ethernet/network devices. In case we increase the number of cpus on a machine, the limiting factor is the fact that cpus have to continually exchange on memory bus those highly touched cache lines that contain refcounters or stats.