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From: mark@parc.xerox.com (Mark Weiser)
Newsgroups: comp.arch
Subject: Re: Paging page tables & SUN4s
Message-ID: <473@roo.UUCP>
Date: 7 Jul 90 03:13:12 GMT
References: <3300142@m.cs.uiuc.edu> <1990Jun29.154940.22762@tera.com> <2936@skye.ed.ac.uk> <1990Jul06.003628.2633@esegue.segue.boston.ma.us> <1122@sirius.ucs.adelaide.edu.au>
Sender: news@parc.xerox.com
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In article <1122@sirius.ucs.adelaide.edu.au> francis@chook.ua.oz.au (Francis Vaughan) writes:

>...
>The hit for SS-1s (and this includes SS-1+s) is that you don't get the sort
>of improvement you would expect in performance when adding much more than
>about 16MB of memory, especially if there is little image sharing.

Good message.  But you say that the problem is especially bad if there
is little image sharing.  Turns out this is irrelevant, or negative.
SunOS does not recognize the sharing in its pmeg algorithms, so it
does not help.  And it can make things worse by causing many more
different little pmegs to be allocated because the sharing forces
many different address to be in use all over the place.  We have a program
which shows pmeg use by process, and shared libraries makes the pmeg problem
much worse: 3-4 pmegs for the shared libraries, replicated for every
copy of the shared library in use (sharing not recognized, remember)?

>" This product features: IMPROVED MEMORY MANAGEMENT; ..."
>" This easy to install unbundled software dramaticly increases Sun 
>SPARCserver performance with database applications ..."
>"...increased system throughput and improved response times particularly 
>under  heavy system loads. Maximum throughput increases up to 50% while 
>supporting up to five times as many concurrent users."

I certainly hope Sun does something about this, and not as an extra
product, but a bug fix available to all.  Selling a 15 MIP machine that
slows down to 4 MIPS when using more than about 16MB of memory is
certainly a bug!

-mark
--
Spoken: Mark Weiser 	ARPA:	weiser@xerox.com	Phone: +1-415-494-4406