Article View: comp.arch
Article #21545Re: DMA on RISC-based systems
From: Andrew Klossner
Date: Fri, 02 Jun 1989 19:49
Date: Fri, 02 Jun 1989 19:49
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"basic requirements ... which must be met to be considered
state-of-the art ... [include] dedicated LAN controllers to
handle the low levels of the LAN protocol ..."
This can backfire on you. I've seen more than one example of a very
smart LAN interface board which actually slowed down system throughput,
because its Chevy on-board processor couldn't do nearly as fast a job
as the Formula 1 dragcar that was the main CPU, and the single active
process was blocked waiting for LAN completion.
Ranging a bit, I've also dealt with systems with a fast main CPU, a
SCSI channel, and a wimpy Z8 in the on-disk SCSI controller. Yep, the
Z8 was the overall system bottleneck -- lots of time wasted while it
slooooowly processed all the messages that SCSI bus master and slave
must exchange.
If you're going to buy into off-CPU agents to move I/O around, make
sure that those agents will improve as fast as the CPU, or your future
generation machines will be crippled.
-=- Andrew Klossner (uunet!tektronix!orca!frip!andrew) [UUCP]
(andrew%frip.wv.tek.com@relay.cs.net) [ARPA]
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!uw-beaver!tektronix!orca!frip!andrew From: andrew@frip.WV.TEK.COM (Andrew Klossner) Newsgroups: comp.arch Subject: Re: DMA on RISC-based systems Message-ID: <3480@orca.WV.TEK.COM> Date: 2 Jun 89 19:49:44 GMT References: <46500067@uxe.cso.uiuc.edu> <181@dg.dg.com> <1989May31.163057.543@utzoo.uucp> Sender: nobody@orca.WV.TEK.COM Organization: Tektronix, Wilsonville, Oregon Lines: 24