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From: tve@sprite.berkeley.edu (Thorsten von Eicken)
Newsgroups: comp.parallel
Subject: Re: iPSC/860 Communication Performance
Message-ID: <1991Apr23.165213.10093@agate.berkeley.edu>
Date: 23 Apr 91 16:52:13 GMT
References: <1991Apr23.123808.10313@hubcap.clemson.edu>
Sender: root@agate.berkeley.edu (Charlie Root)
Organization: University of California, Berkeley
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Approved: parallel@hubcap.clemson.edu

In article <1991Apr23.123808.10313@hubcap.clemson.edu> wangjw@cs.purdue.edu () writes:
>  The ipsc/860 hypercube is noted by its very fast processor and circuit
>switching communications. The processor speed is around 9-10 times faster
>than the Ncube/2 as we recently measured. However, the communication
>speed is by far not raised by a comparable rate. This makes people
>dissapointed as they moved their ipsc/2 or Ncube code to this machine
>because the speedup would drop dramatically.

That's what I've been suspecting for a while. I would actually claim
that the ipsc/860 communication is worse than that of the Ncube/2. If you
do it right, it takes 23 instructions to send and 26 to receive a
message on the ncube. This includes both the user and kernel code.
This turns into 10us for a send and about 15us for a receive. As you
probably know, the standard OS takes 8x longer... What's the
peak bandwidth for the ipsc/860? The ncube has 2.2Mb/s/link and
unless you send large (>512bytes) messages, you can keep between
1 and 2 channels busy (large messages can keep more busy).
	Thorsten von Eicken

-- 
=========================== MODERATOR ==============================
Steve Stevenson                            {steve,fpst}@hubcap.clemson.edu
Department of Computer Science,            comp.parallel
Clemson University, Clemson, SC 29634-1906 (803)656-5880.mabell