Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!dcl-cs!aber-cs!aem
From: aem@aber-cs.UUCP (Alec D.E. Muffett)
Newsgroups: comp.unix.ultrix
Subject: Re: 58n0
Summary: SMP is half-baked for the 58n0 family...
Message-ID: <2045@aber-cs.UUCP>
Date: 1 Oct 90 13:50:00 GMT
References: <1990Sep26.095834.3744@ircam.ircam.fr> <2906@canisius.UUCP> <1990Sep30.123350.14441@ircam.ircam.fr>
Reply-To: aem@odin.UUCP (Alec D.E. Muffett)
Organization: Computer Unit UCW Aberystwyth
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In article <1990Sep30.123350.14441@ircam.ircam.fr> mf@ircam.ircam.fr (Michel Fingerhut) writes:

>1.  What are the problems as known to DEC today (so that we're less
>    pissed off when we encounter them).

Here in Aberystwyth we are running 2x DEC 5830's with Rev 179 Ultrix 4.0.
We have observed that the Symmetric Multi-Processing behaves badly under
a low machine load and are therefore permamently running 2 low-priority
cpu-burning jobs which sleep for bursts of 15 seconds if the load
average goes >4.0.

When these jobs are running, the performance is greatly improved, we
believe this is because the presence of the two jobs (1 per spare CPU)
solves some sort of ordering problem in the scheduler.  DEC definitely
DO know about this, it has appeared on a list of SPR's sent to us.  No
solution is yet forthcoming, but we live in hope...

It's not the perfect solution, because the two jobs tend to eat away at
the cpu, and if some user puts a heavily i/o bound job up as well, the
machine starts to groan.  Then we just kill them fast and put them back
later... 

So, DEC have given us the ultimate reciprocal machine...  the more load
you put on it, the faster it goes...  8)

alec (and robert :-) )