From owner-sc22wg5@open-std.org Thu Oct 22 14:25:17 2009 Return-Path: X-Original-To: sc22wg5-dom8 Delivered-To: sc22wg5-dom8@www2.open-std.org Received: by www2.open-std.org (Postfix, from userid 521) id 56227C76BC4; Thu, 22 Oct 2009 14:25:17 +0200 (CET DST) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from mail1.cray.com (mail1.cray.com [136.162.62.100]) by www2.open-std.org (Postfix) with ESMTP id 924BBC76BB7 for ; Thu, 22 Oct 2009 14:25:16 +0200 (CET DST) Received: from beaver.us.cray.com (beaver.us.cray.com [172.30.74.51]) by mail1.cray.com (8.13.6/8.13.3/gw-5323) with ESMTP id n9MCPEqH028038 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=FAIL); Thu, 22 Oct 2009 07:25:14 -0500 (CDT) Received: from cfexcas02.americas.cray.com (cfexcas02-2.us.cray.com [172.30.74.228]) by beaver.us.cray.com (8.13.8/8.13.3/hub-5273) with ESMTP id n9MCPDDS003617; Thu, 22 Oct 2009 07:25:13 -0500 Received: from bill-longs-macbook-pro.local (192.168.239.32) by cfexcas02.americas.cray.com (172.30.74.226) with Microsoft SMTP Server (TLS) id 8.1.393.1; Thu, 22 Oct 2009 07:25:13 -0500 Message-ID: <4AE04F43.9050401@cray.com> Date: Thu, 22 Oct 2009 07:25:39 -0500 From: Bill Long Reply-To: Organization: Cray Inc. User-Agent: Thunderbird 2.0.0.23 (Macintosh/20090812) MIME-Version: 1.0 To: fortran standards email list for J3 Cc: SC22WG5 Subject: Re: (j3.2006) (SC22WG5.4109) [ukfortran] Standard intrinsics and coarrays References: <20091020111544.C0F5CC178E3@www2.open-std.org> <20091020154252.946EAC178E3@www2.open-std.org> <20091021161933.1B2FCC178E3@www2.open-std.org> <20091021171501.21FA4C178E3@www2.open-std.org> <20091021175702.E4D26C178E3@www2.open-std.org> <20091022043326.83DB9C178E4@www2.open-std.org> <20091022051613.0AEF5C178E4@www2.open-std.org> <20091022062554.CF066C178E4@www2.open-std.org> <20091022115243.E875EC178E4@www2.open-std.org> In-Reply-To: <20091022115243.E875EC178E4@www2.open-std.org> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Cray-VirusStatus: clean Sender: owner-sc22wg5@open-std.org Precedence: bulk N.M. Maclaren wrote: > > Systems with suitable compare-and-swap hardware can implement > parallel use of a shared RANDOM_NUMBER safely without locking. Adding > RANDOM_SEED to the mix makes that much trickier, and it's not something > that any sane programmer would do, anyway. > As a (my) performance rule of thumb, if you can generate 1.e9 64-bit values per second you are OK. In some cases, 1.e8 might be considered. Even with hardware compare-and-swap, a shared generator on an even modest sized system will have trouble with this. The scheme has no chance of scaling to large numbers of images. And it still fails the reproducibility requirement. Cheers, Bill -- Bill Long longb@cray.com Fortran Technical Support & voice: 651-605-9024 Bioinformatics Software Development fax: 651-605-9142 Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120