Dieter wrote:
Video decoding is hard to parallelize on general purpose
CPUs. Thus even if it has two ALUs, you will not be able
to use both to their full potential. Specialized video
decoding hardware is much better in that case.
Also keep in mind, that having two processors does not
mean you have doubled your processing power. How much
you get depends a lot on:
1) How well you can parellize the work tasks.
One way to parallelize a process is splitting it up into pieces
that can run independently in serial, then running it on a SMP
machine. AMD's x2 chips are coming down in price, and x4 chips
should be available soon. So this is starting to become practical.
The trick will be figuring out how and where to divide a monolithic
program into pieces. Ideally you'd want each piece to take about
tha same amount of CPU, since SMP machines usually have identical
CPUs. And pieces that the GPU can do would ideally go at the end
to avoid having to ship data back and forth.
I don't know if this is possible with MPEG decoding. I think that it
lends itself more to hardware acceleration.
IIRC, this was one of the goals of JPEG 2k -- to design it so that it
could be done by multiple processors running multiple threads.
If the MPEG decoding requires a lot of X pixel IDCTs then special
purpose hardware that can rapidly do an X pixel IDCT would be a great
help. This would work best if it could be pipelined since the pipe is
going to be rather long. Also, IIUC, the code contains a lot of MACs
and requires multiple accumulator registers and s system that is SIMD.
In both cases, these are hardware accelerators that accelerate a single
thread. OTOH, there is the fractional pixel block move which could
operate in parallel, but still in a single thread.
--
JRT
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