Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!uwvax!tank!uxc!uxc.cso.uiuc.edu!ux1.cso.uiuc.edu!uxe.cso.uiuc.edu!sandrock
From: sandrock@uxe.cso.uiuc.edu
Newsgroups: comp.arch
Subject: DMA on RISC-based systems
Message-ID: <46500067@uxe.cso.uiuc.edu>
Date: 24 May 89 20:31:00 GMT
Lines: 25
Nf-ID: #N:uxe.cso.uiuc.edu:46500067:000:1596
Nf-From: uxe.cso.uiuc.edu!sandrock    May 24 15:31:00 1989


I am interested in the pros and cons of DMA transfers in RISC systems.
In particular I am interested in the notion that the DECsystem 3100 has
no DMA to its main memory, but instead relies upon the CPU to copy i/o
buffers to/from an auxilliary memory. First, is this statement accurate?
And second, if true, is this a reasonable tradeoff to make on a RISC system?
We are interested in the DECsystem 3100 (allegedly same h/w as DECstation)
versus the MIPS M/120 as far as multiuser (32 simultaneous, say) performance.
The load would likely be a mix of compute-bound and i/o-bound applications,
including possibly Ingres and NFS-serving, along with various chemistry codes.
Also, wrt RISC systems, would we be better off segregating the interactive
usage, i.e., editing, email, etc. from the compute-bound batch-mode jobs, by
running them on two separate systems?  My thinking is that a high rate of
context switching caused by interactive processes would tend to counteract
the advantage of having large instruction and data caches on the machine.
Any pertinant advice is welcome, and I will summarize if need be.

Mark Sandrock

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BITNET:   sandrock@uiucscs	    University of Illinois at Urbana-Champaign
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