On Tue, 13 Jan 2004, Ralf Baechle wrote:
> > You cannot modify the size of the primary caches -- the values are
> > hardwired to the amount of cache available in the processor (8kB+8kB for
> > the original R4000). However, if you take appropriate precautions, you
> > can alter the line sizes of the caches by modifying appropriate bits of
> > cp0.config.
>
> On some systems that's a dangerous and won't work due to some issue with
> the memory controller. That's why Linux supports all possible combinations
> instead of reconfiguring caches. Of course there's also the hope that
> developers of a system did configure the cache for the optimal performance.
Plus there are processor errata related to certain values of line sizes.
> If reconfiguring is possible 32-byte D-cache and I-Cache lines are probably
> the optimum for non-tiny systems. For the L2 cache I'd guess 64 or 128
> byte lines.
Well, reconfiguring the line size of the L2 cache is system-specific and
the size is most likely hardwired.
BTW, the DECstation uses 16-byte lines for the D-cache and the I-Cache
and 32-byte lines for the S-cache. With the S-cache size at 1MB and up to
480MB of RAM does it qualify as a tiny system? ;-)
Maciej
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +
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