[theora-dev] [OT] Just saying hi!

[Christoph Lampert]

On Thu, 27 Feb 2003, Mike Melanson wrote:
> > with large gaps, prefetch seems absolutely necessary. The problem is just
> > that good prefetch depends very much on the underlying CPU, memory and
> > it's speed... 
> 
> 	I have suddenly become very conscious of cache and pre-fetching
> issues. I found out the SH-4 has a whopping 16 kilobytes of data
> cache...:) It does have a prefetch instruction capable of fetching 32 byte
> blocks into the data cache. And the CPU manual listed no caveats about the
> reliability of the instruction (I understand that Intel CPU prefetch
> instructions are not guaranteed to do anything).

I rather meant that prefetch instructions have to be executed at the right
time in order to have the memory avaible at the right time. If executed
too late, memory latency isn't lowered enough. If the cache is small and
prefetch executed too early, data is already overwritten before it can be
used. Thus the right position depends very much on memory and CPU
architecture. But a console with fixed architecture is of course a
great benefit for these questions. :) 

Christoph 

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