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Re: Second level cache?

To: riscy@pyramid.com
Subject: Re: Second level cache?
From: Alan Krantz <atk@agua.Colorado.EDU>
Date: Mon, 9 Aug 93 09:13:39 MDT
Reply-to: riscy@pyramid.com
Sender: owner-riscy@pyramid.com
  > From owner-riscy@pyramid.com Mon Aug  9 08:53:13 1993
  > Status: R

  > Somebody mentioned that some research needs to be done on how a second 
  > cache will effect performance.  Any suggestions on how to do this?

  > Based on observation it seems that a cache is worth it, SGI mips 4000 SC is
  > around 35/34 and the mips 4000 PC is around 60/58 specint/specfp.

  > Adding the decreased locality of Unix+X11 over dos, the higher (100 Mhz
  > internal) clock rate, and mips binaries being bigger then 486 it would
  > seem that a large secondary cache would be necessary.  Based on a 486's
  > secondary cache being useful.

The subject isn't that simple. For example the usefulness of the cache 
greately depends on how the memory is interleaved (the R4xxx has an external
64 bit path way). Also there is an issue of the internal cache size. An
internal cache on a 486 is 16k (I think 8k each for I&D) (but writethrough not
write back). The R4xxxx has a larger internal cache.

  > Any suggestions on how to get some numbers experimentally?

Yea build an R4000 system with the desired level of interleaving; one with
and one without secondary cache. Then run both systems :)


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