[rescue] Re: Re: OH YEA??? [was: Re: Ultra?]

[Gavin Hubbard]

Dave said:

<<
 It depends *entirely* on the kind of code running on the processor.
A cache will rarely negatively impact performance in any real way, but
if the code in question is "cache friendly" a larger cache can be a
big win.  It's certainly reasonable that, for a given OS and
application software mix, that you might not see any benefit from a
larger cache.  There are other attributes of cache design that come
into play...cache type (write through, write back, etc), line size,
etc...that can also have a dramatic effect on performance given
certain memory access patterns.
>>

IIRC there are some major performance problems associated with processor
caches in multiprocessor systems. The memory subsystem works hard to keep
the cache data coherent between different processors. If a read-only memory
region, used by all of the processors, shares a cache line with another
memory region that is being updated frequently by another processos, the
caches will spend a lot of time updating their copy of the cache line i.e.
"cache sloshing". This can kill the performance of the system if you're not
careful.

(I know you know this)

Regards,

Gavin