Path: utzoo!attcan!uunet!mcvax!kth!draken!ttds!jonasn
From: jonasn@ttds.UUCP (Jonas Nygren)
Newsgroups: comp.arch
Subject: Re: DMA on RISC-based systems
Message-ID: <1219@ttds.UUCP>
Date: 10 Jun 89 01:20:35 GMT
References: <46500067@uxe.cso.uiuc.edu> <181@dg.dg.com> <185@dg.dg.com> <1213@ttds.UUCP> <8499@june.cs.washington.edu>
Reply-To: jonasn@ttds.UUCP (Jonas Nygren)
Organization: The Royal Inst. of Techn., Stockholm
Lines: 36

In article <8499@june.cs.washington.edu> rik@june.cs.washington.edu (Rik Littlefield) writes:
>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

My figures was intended to show the upper limit of througput on a comercial
available workstation. I have been informed by people inside Digital that 
it would be possible to achieve figures at least twice what I stated if
you care to look for disk-drive sources outside Digital.

/jonas