Newsgroups: comp.parallel
From: Joel Williamson <joelw@convex.convex.com>
Subject: Re: Help - explain superlinear speedup?
Organization: Engineering, Convex Computer Corporation, Richardson, Tx USA
Date: Fri, 13 Jan 1995 17:16:34 GMT
Message-ID: <3f61t5$etd@mozart.convex.com>

In article <3f23ht$ec9@agate.berkeley.edu>,
Steve Slater <slater@nuc.berkeley.edu> wrote:
>
>I have a program which has superlinear speedup and I
>can't explain it. Does anyone have any ideas. Here is
>the summary.
>

	...(summary partially deleted)...

>You would expect less than linear speedup since with
>only one machine, no messages are sent over the ethernet,
>they are just communicated via sockets. But I get very
>superlinear speedup like:
>
>1 proc:  556 sec               4 unique processes on 1 machine
>2 proc:  204 sec               2 processes on each of 2 machines
>4 proc:   38 sec               1 process on each machine
>
>There was NO memory swapping occurring during the entire
>execution time. I would periodically check with ps.
>
>Does anyone have any thoughts?
>
>Thanks,
>
>Steve Slater
>slater@nuc.berkeley.edu
>

Superlinear speedups always result from additional resources (almost
always memory) relieving bottlenecks in the computation.  So either the
additional physical memory eliminated some paging and/or the problem fit
in cache once you got to four processors.

Best regards,

Joel Williamson
-- 



