Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 21 Jun 2002 02:26:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 21 Jun 2002 02:26:03 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:15470 "EHLO frodo.biederman.org") by vger.kernel.org with ESMTP id ; Fri, 21 Jun 2002 02:26:02 -0400 To: Linus Torvalds Cc: Cort Dougan , Benjamin LaHaise , Rusty Russell , Robert Love , Linux Kernel Mailing List Subject: Re: latest linus-2.5 BK broken References: From: ebiederm@xmission.com (Eric W. Biederman) Date: 21 Jun 2002 00:15:54 -0600 In-Reply-To: Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1 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: 3632 Lines: 78 Linus Torvalds writes: > On Thu, 20 Jun 2002, Cort Dougan wrote: > > > > "Beating the SMP horse to death" does make sense for 2 processor SMP > > machines. > > It makes fine sense for any tightly coupled system, where the tight > coupling is cost-efficient. > > Today that means 2 CPU's, and maybe 4. > > Things like SMT (Intel calls it "HT") increase that to 4/8. It's just > _cheaper_ to do that kind of built-in SMP support than it is to not use > it. > > The important part of what Cort says is "commodity". Not the "small number > of CPU's". Linux is focusing on SMP, because it is the ONLY INTERESTING > HARDWARE BASE in the commodity space. Commodity is the wrong word. Volume is the right word. Volumes of machines, volumes of money, and volumes of developers. > ccNuma and clusters just aren't even on the _radar_ from a commodity > standpoint. While commodity 4- and 8-way SMP is just a few years away. I bet it is easy to find a easy to find a 2-4 way heterogenous pile of computers in many a developers personal possession that could be turned into a cluster if the software wasn't so inconvenient to use, or if there was a good reason to run computer systems that way. Clusters and ccNuma are entirely different animals. ccNuma is about specialized hardware. Clusters are about using commodity hardware in a different way. > So because SMP hardware is cheap and efficient, all reasonable scalability > work is done on SMP. And the fringe is just that - fringe. The > numa/cluster fringe tends to try to use SMP approaches because they know > they are a minority, and they want to try to leverage off the commodity. The cluster fringe is a minority. But the high performance computer and batch scheduling minority has done a lot of work of the theoretical, and developmental computer science in the past. And I would be surprised if they weren't influential in the future. But like most research a lot of it is trying suboptimal solutions that eventually get ditched. The only SMP like stuff I have seen in clustering are the attempts to make clusters simpler to use. And the question I hear is how simple can we make it without sacrificing scaleabilty. > And it will continue to be this way for the forseeable future. People > should just accept the fact. I apparently see things differently. That the clusters will be a minority certainly. That the people working on them are hopelessly in fringes not a bit. Clusters of Linux machines scale acceptably . And for a certain set of people get the job done. The problem is making it more convenient to get the job done. And just like in hardware as integration can make extra hardware features essentially free, the next step is to begin integrating cluster features into Linux both kernel and user space. Basically the technique is. Implement something that works. Then find the clean efficient way to do it. If that takes kernel support write a kernel patch, and get it in. > And I guarantee Linux will scale up fine to 16 CPU's, once that is > commodity. And the rest is just not all that important. It works just fine on my little 20 node 20 kernel test machine too. I think Larry's perspective is interesting and if the common cluster software gets working well enough I might even try it. But until a big SMP becomes commodity I don't see the point. Eric - 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/