Re: Memory upgrade causes slowdown; why?

Mark Levitt (melevitt@syr.edu)
Wed, 23 Oct 1996 00:14:37 -0400 (EDT)

On Tue, 22 Oct 1996, Shawn Rutledge wrote:
> I just upgraded my system from 16 megs to 32 megs, and now Linux crawls
> (so bad that I took the new SIMM back out, temporarily I hope!) X takes
> 2 or 3 times as long to start up, kernel builds take longer, that sort of
> thing. I remember somebody else asking that question and getting an
> answer sometime in the last few months...

What size is your L2 cache? What's happening is that the top 16megs
(from >16 to 32) is not being cached. Since Linux uses memory from the
top down (so to speak), most of you memory access is not being held in
the cache and the cpu has to go out to main memory. That's why you are
seeing the significant speed decrease.

Now, if you have 256k of cache or more, the L2 cache *should* be able
to handle 32 megs (at least mine does), however it may be that your
motherboard can only cache the first 16. If you can add more L2 cache,
or figure out how to get your entire memory space cached, it will solve
the problem.

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Mark E. Levitt
Department of Speech Communication, Syracuse University
E-mail: melevitt@syr.edu
Home Page: http://web.syr.edu/~melevitt

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