Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!uflorida!bernhold
From: bernhold@red (David E. Bernholdt)
Newsgroups: comp.lang.fortran
Subject: Cray memory stride (was Re: vectorization question reposed)
Message-ID: <27758@uflorida.cis.ufl.EDU>
Date: 30 Mar 91 22:24:19 GMT
References: <1991Mar30.142903.5225@ariel.unm.edu>
Sender: news@uflorida.cis.ufl.EDU
Organization: Quantum Theory Project, Univ. of Florida
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In article <1991Mar30.142903.5225@ariel.unm.edu> prentice@triton.unm.edu (John Prentice) writes:
>One other question.  What is the size of the memory banks on the 
>YMP and hence what strides should you avoid?

I asked this question a while ago.  I _think_ that the (two) YMPs to
which I have access have 256 banks.  In general, there are a wide
range of possible bank configurations for a given type of Cray.
Unicos has a command and a system call called "target" which report
type of Cray, memory size, number of banks, clock period, etc. for the
host in question. The system call has to be made via a C routine, but
in Unicos it is fairly easy to call C from Fortran.

Once you've got the number of banks, the most general thing to do is
to work with vectors who's length is prime relative to the number of
banks.

One caveat on the "target" command/call:  the reponse returned can be
configured by the system manager, though I'm not sure I see the value
in "lying" about the machine's configuration.
-- 
David Bernholdt			bernhold@qtp.ufl.edu
Quantum Theory Project		bernhold@ufpine.bitnet
University of Florida
Gainesville, FL  32611		904/392 6365