From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261240AbTICG4J (ORCPT ); Wed, 3 Sep 2003 02:56:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261332AbTICG4J (ORCPT ); Wed, 3 Sep 2003 02:56:09 -0400 Received: from anumail4.anu.edu.au ([150.203.2.44]:65227 "EHLO anu.edu.au") by vger.kernel.org with ESMTP id S261240AbTICG4F (ORCPT ); Wed, 3 Sep 2003 02:56:05 -0400 Message-ID: <3F55907B.1030700@cyberone.com.au> Date: Wed, 03 Sep 2003 16:55:55 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2.1) Gecko/20021130 MIME-Version: 1.0 To: Anton Blanchard CC: Larry McVoy , Larry McVoy , linux-kernel@vger.kernel.org Subject: Re: Scaling noise References: <20030903040327.GA10257@work.bitmover.com> <20030903041850.GA2978@krispykreme> <20030903042953.GC10257@work.bitmover.com> <20030903062817.GA19894@krispykreme> In-Reply-To: <20030903062817.GA19894@krispykreme> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Sender-Domain: cyberone.com.au X-Spam-Score: (-3) X-Spam-Tests: EMAIL_ATTRIBUTION,IN_REP_TO,QUOTED_EMAIL_TEXT,REFERENCES,REPLY_WITH_QUOTES,USER_AGENT_MOZILLA_UA Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Anton Blanchard wrote: >>>>I've frequently tried to make the point that all the scaling for >>>>lots of processors is nonsense. Mr Dell says it better: >>>> >>>> "Eight-way (servers) are less than 1 percent of the market and >>>> shrinking pretty dramatically," Dell said. "If our competitors >>>> want to claim they're No. 1 in eight-ways, that's fine. We >>>> want to lead the market with two-way and four-way (processor >>>> machines)." >>>> >>>>Tell me again that it is a good idea to screw up uniprocessor >>>>performance for 64 way machines. Great idea, that. Go Dinosaurs! >>>> >>>And does your 4 way have hyperthreading? >>> >>What part of "shrinking pretty dramatically" did you not understand? >>Maybe you know more than Mike Dell. Could you share that insight? >> > >Ok. But only because you asked nicely. > >Mike Dell wants to sell 2 and 4 processor boxes and Intel wants to sell >processors with hyperthreading on them. Scaling to 4 or 8 threads is just >like scaling to 4 or 8 processors, only worse. > >However, lets not end up in a yet another 64 way scalability argument here. > >The thing we should be worrying about is the UP -> 2 way SMP scalability >issue. If every chip in the future has hyperthreading then all of sudden >everyone is running an SMP kernel. And what hurts us? > >atomic ops >memory barriers > >Ive always worried about those atomic ops that only appear in an SMP >kernel, but Rusty recently reminded me its the same story for most of the >memory barriers. > >Things like RCU can do a lot for this UP -> 2 way SMP issue. The fact it >also helps the big end of town is just a bonus. > I think LM advocates aiming single image scalability at or before the knee of the CPU vs performance curve. Say thats 4 way, it means you should get good performance on 8 ways while keeping top performance on 1 and 2 and 4 ways. (Sorry if I mis-represent your position). I don't think anyone advocates sacrificing UP performance for 32 ways, but as he says it can happen .1% at a time. But it looks like 2.6 will scale well to 16 way and higher. I wonder if there are many regressions from 2.4 or 2.2 on small systems.