From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on yquem.inria.fr X-Spam-Level: X-Spam-Status: No, score=0.0 required=5.0 tests=none autolearn=disabled version=3.1.3 X-Original-To: caml-list@yquem.inria.fr Delivered-To: caml-list@yquem.inria.fr Received: from mail4-relais-sop.national.inria.fr (mail4-relais-sop.national.inria.fr [192.134.164.105]) by yquem.inria.fr (Postfix) with ESMTP id 2BCD4BBAF for ; Thu, 10 Jul 2008 16:01:34 +0200 (CEST) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AvwAAHOzdUjUnw7VfGdsb2JhbACCOJAjAQELBQgHEQOeOw X-IronPort-AV: E=Sophos;i="4.30,338,1212357600"; d="scan'208";a="27203531" Received: from ptb-relay02.plus.net ([212.159.14.213]) by mail4-smtp-sop.national.inria.fr with ESMTP/TLS/AES256-SHA; 10 Jul 2008 16:01:33 +0200 Received: from [90.192.139.4] (helo=beast.local) by ptb-relay02.plus.net with esmtpa (Exim) id 1KGwiB-0006dg-Ti; Thu, 10 Jul 2008 15:01:32 +0100 From: Jon Harrop Organization: Flying Frog Consultancy Ltd. To: peng.zang@gmail.com, caml-list@yquem.inria.fr Subject: Re: [Caml-list] thousands of CPU cores Date: Thu, 10 Jul 2008 15:00:02 +0100 User-Agent: KMail/1.9.9 References: <200807100944.29221.peng.zang@gmail.com> In-Reply-To: <200807100944.29221.peng.zang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200807101500.03079.jon@ffconsultancy.com> X-Plusnet-Relay: 6dbba60fd5de2fa6f0c60d0d60191cef X-Spam: no; 0.00; coherence:01 ocaml:01 run-time:01 parallelism:01 parallelism:01 ocaml:01 ocaml's:01 peng:98 cnet:98 cnet:98 researched:98 frog:98 wrote:01 exception:01 caml-list:01 On Thursday 10 July 2008 14:44:25 Peng Zang wrote: > On Thursday 10 July 2008 01:57:44 am J C wrote: > > I know that Caml team wanted to see if many-core shared-memory systems > > were going to stick around before bothering with Caml development that > > takes advantage of them. > > > > Well, it looks like they are here to stay, after all: > > > > http://news.cnet.com/8301-13924_3-9981760-64.html > > This article doesn't say anything about whether the many-core system will > be shared-memory. Remember, a shared memory architecture has to deal with > cache and memory coherence. The prevailing view is that the overhead for > such an approach does not scale. For massively parallel computation we > must turn to message passing or barrier/sync paradigms. > > I am doubtful that a thousand core machine will be shared-memory based. Today's biggest shared-memory supercomputers already have thousands of cores. > Also, this is a CNET article.. not exactly known for being in depth or well > researched and this article is no exception. It is an article based > entirely on a few speculative comments of some Intel guys. I wouldn't take > it too seriously. > > Personally, I can see why the Caml development team opted not to put effort > into dealing with shared-memory systems. The OCaml development team put huge effort into their concurrent run-time. > It is a stop-gap solution... That is not true. Many-core machines will always be decomposed into shared-memory clusters of as many cores as possible because shared memory parallelism will always be orders of magnitude more efficient than distributed parallelism. OCaml is already ~8x slower than F# on today's eight core desktops. If OCaml's shortcomings are not remedied then it will become exponentially slower than parallelized languages like F# over the next few years until we reach the limit of shared memory parallelism in ~10 years time. Consequently, the parallel GC scheduled for this summer will be the single most important development in OCaml world ever. -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. http://www.ffconsultancy.com/products/?e