From: a080700@hp9000.csc.cuhk.hk (Stephen Wong S M) Subject: Re: Performance Enhanced or Worsened by Cache Addition? On Zeos 486DX2-66 system? Date: Thu, 7 Jan 1993 11:30:57 GMT
In article <FRIEDMAN.93Jan7000112@khan.trincoll.edu> mark.friedman@mail.trincoll.edu writes:
>On some PC-Clone systems, when running some versions of Unix, users
>have found that performance actually increases after disabling the
>hardware cache perhaps because the cacheing algorithm in the kernel
>was better tuned to Unix access than the hardware cacheing algorithms.
>
>Can anyone argue through an understanding of Linux's kernel and
>hardware cacheing, or through experience, or best yet actual
>measurements whether the performance of Linux with X, and say GNU
>programs such as emacs and gcc increases or decreases with the
>addition of a hardware cache?
>
>In particular, I'd be interested in knowing if any Zeos 486DX2-66
>system users have measured/experienced their systems running Linux
>with and without the 128K and 256K hardware caches and experie nced a
>significant difference in performance in either direction.
>
>I am trying to decide whether to purchase a 128K cache upgrade to go
>with a system with 16M RAM.
>
>Thanks,
>
>-- Mark
>--
>
>
>Mark A. Friedman mark.friedman@mail.trincoll.edu
>Engineering and Computer Science or friedman@starbase.trincoll.edu
>Trinity College Phone: (203) 297-2519
>Hartford, Connecticut 06106 Fax: (203) 297-2569
You must be mixed up disk cache with CPU cache. In general, no flame, no
flame please, disk cache can be implemented quite good by kernel code, as
in linux, and therefore, you may be better to use software disk cache,
rather than cached harddisk controller. However, CPU cache is totally
different story. The kernel cannot speed up main memory (RAM) access by
software method! Unless the CPU cache design is really bad.
You will be quite sure to gain some speed in increasing CPU cache size.
However, there is deminishing return in adding CPU cache. Let say, if
you add extra 32kB secondary cache on top of the 8kB internal cache in
486DX, you will really feel the difference in speed. On the other hand,
if you add extra 256kB CPU cache on top of a system which already has
256kB, you may not tell the difference!
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