From owner-sc22wg5@open-std.org Thu Jan 22 19:56:41 2009 Return-Path: X-Original-To: sc22wg5-dom7 Delivered-To: sc22wg5-dom7@www2.open-std.org Received: by www2.open-std.org (Postfix, from userid 521) id E81A0CA5FE6; Thu, 22 Jan 2009 19:56:41 +0100 (CET) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from mail1.cray.com (mail1.cray.com [136.162.0.111]) by www2.open-std.org (Postfix) with ESMTP id D8CA4CA3439 for ; Thu, 22 Jan 2009 19:56:39 +0100 (CET) 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 n0MIuXEi009008 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 22 Jan 2009 12:56:33 -0600 (CST) Received: from CFEXFE01.us.cray.com (cfexfe01.us.cray.com [172.30.74.93]) by beaver.us.cray.com (8.13.8/8.13.3/hub-5273) with ESMTP id n0MIuWmO023897; Thu, 22 Jan 2009 12:56:32 -0600 Received: from mh-dhcp-172-31-16-180.us.cray.com ([172.31.16.180]) by CFEXFE01.us.cray.com over TLS secured channel with Microsoft SMTPSVC(6.0.3790.3959); Thu, 22 Jan 2009 12:56:32 -0600 Message-ID: <4978C20F.2070207@cray.com> Date: Thu, 22 Jan 2009 12:59:27 -0600 From: Bill Long Reply-To: longb@cray.com Organization: Cray Inc. User-Agent: Thunderbird 2.0.0.9 (Macintosh/20071031) MIME-Version: 1.0 To: fortran standards email list for J3 Cc: mpi3-fortran@lists.mpi-forum.org, WG5 Subject: Re: (j3.2006) (SC22WG5.3891) [MPI3 Fortran] [ukfortran] [MPI3 Fortran] MPI non-blocking transfers References: <20090122100652.C31E9CA3434@www2.open-std.org> <4978A8A0.8090407@cray.com> <20090122175730.8BA1BCA3439@www2.open-std.org> In-Reply-To: <20090122175730.8BA1BCA3439@www2.open-std.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 22 Jan 2009 18:56:32.0387 (UTC) FILETIME=[24287D30:01C97CC3] X-Cray-VirusStatus: clean Sender: owner-sc22wg5@open-std.org Precedence: bulk Aleksandar Donev wrote: > On Thursday 22 January 2009 09:10, Bill Long wrote: > > >> If we use a different name, like >> ASYNC_EXTERNAL, is there any difference between that and VOLATILE? I >> suspect not. >> > Yes, I explained this a long time ago, many times, but we go in circles > again. > For one thing, VOLATILE has some ill-defined semantics. > Vendors seem to know what to do. The VOLATILE concept is utterly trivial to implement. > For two, VOLATILE disables all optimization. Only for statements that might involve references or definitions of a volatile variable. The rest of the code can be optimized normally. Which is exactly what we need here. > ASYNCHRONOUS only disables > code motion accross waits and certain argument associations (such as > more care with copy in/out). The rest of the code can be optimized as > usual. If that's the case, then there is a serious problem with ASYNCHRONOUS, as illustrated by Nick's examples. In most places in a code, VOLATILE and ASYNCHRONOUS have exactly the same effect on optimization. In fact, the simplest implementation of ASYNCHRONOUS that is semantically safe is to make is synonym for VOLATILE. > Surely this is important for a high-performance library like > MPI. > The high performance part of MPI occurs inside the library routines. That's unaffected by the declaration of the buffer outside. > >> The other is that it incorrectly suggests that MPI calls >> have something to do with I/O which is not the case (except for the >> actual MPI I/O calls >> > And I already explained this a long time ago, and even quoted you the > Wikipedia definition of I/O. But if you care not to listen, that is > fine, let's continue going in circles. > I forgot that I was addressing more than the Fortran list. I meant that MPI has nothing to do with the Fortran concept of I/O (not Wikipedia's). When we're talking about a Fortran's asynchronous attribute, it seems reasonable to relate it to Fortran's concept of I/O. Cheers, Bill > Best, > Aleks > > _______________________________________________ > J3 mailing list > J3@j3-fortran.org > http://j3-fortran.org/mailman/listinfo/j3 > -- 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