Path: utzoo!attcan!uunet!cs.utexas.edu!rutgers!mit-eddie!uw-beaver!uw-june!rik
From: rik@june.cs.washington.edu (Rik Littlefield)
Newsgroups: comp.arch
Subject: Re: DMA on RISC-based systems
Message-ID: <8499@june.cs.washington.edu>
Date: 8 Jun 89 18:24:40 GMT
References: <46500067@uxe.cso.uiuc.edu> <181@dg.dg.com> <185@dg.dg.com> <1213@ttds.UUCP>
Organization: U of Washington, Computer Science, Seattle
Lines: 28

In article <1213@ttds.UUCP>, jonasn@ttds.UUCP (Jonas Nygren) writes:
< In article <8479@june.cs.washington.edu> rik@june.cs.washington.edu (Rik Littlefield -- that's me) writes:
< < In article <185@dg.dg.com>, rec@dg.dg.com (Robert Cousins) writes:
< < < Given that a disk channel will be averaging 200K bytes/second ...
< <
< < I suspect that workstation class systems have an *average* disk
< < throughput that is at least 10X lower than this number, even when
< < they are working full out.
< <
< < Would someone with real utilization numbers care to fill us in?
< 
< I have performed a small test on a DECstation3100 with a RZ55-230 Mb disk.
< The test used 15 processes reading/writing 2Mb files each, with the following
< results:
<  <stuff deleted> 
< Mean value: 234 kb/s

Sure, but how much of the time does your workstation run 15 processes reading
and writing the disk as fast as it can?  Program loads and file copies run at
200 Kb/sec, program builds do maybe 10X less I/O, SPICE just crunches.
Whether DMA (or any other feature) is worthwhile depends on what the machine
spends its time doing.

Apparently my question was not clear, so I will restate it.  Does anybody have
numbers that reflect actual usage over an extended period?  If so, please tell
us what sort of work was being done, and how much I/O was required to do it.

--Rik