It is a very interesting point of view.

From a practical point of view, the Dual REAL physical processor will be
faster than an HyperThreading single physical Processor system in many case,
I agree. And I will be very happy if you buy two processors, instead of one
;-)

On the other side, we saw a lot of funky thinks when you have multithreaded
applications, like video decoding, or 3D pipelines using multiple threads,
because some time, the CPU2 ask a write combine from the CPU1 and that is
colliding with the regular memory traffic. (the L2 caches from CPU1 and CPU2
dispute the ownership of the data) In the case of Hyperthreading, we do not
see this. The return on investment, from a processing power point of view is
much better with Hyperthreading.

Hyperthreading was design to increase the decoding capability of your
processors, right now, the decoder is the bottle neck in your processor.
Your execution units are not fully used, due to the fact that your rendering
place a lot of memory request and wait for the answers (300 to 400 Cycles)
in a regular CPU, you will be waiting for the cache line to arrive via the
front side bus and do NOTHING, with hyperthreading, the second logical CPU
will have 300 cycles to do what ever it wants, from reading from L1 or L2
cache, to crunching data with int or float. It is a huge room for
improvement, specially for programs like PovRay that use a lot of memory.

By the way, I speak a little german, so I tried to understand how you did
implement the multithreading, and I was not able the figure out, can you
explain?
Can you share the source code?

Remember, Hyperthreading just improve the return on investment of each
transistor in the Processor, and that is a big deal if you are looking for
Processing power.

Francois




"Theo Gottwald *" <The### [at] t-onlinede> wrote in message
news:3d5677bd@news.povray.org...
> Sounds really good.
>
> However the speed increase in Hyperthreading is diffrent to true
> "smp-multiprocessing-systems".
>
> while in multiprocessing systems you have a REAL SECOND FPU, you have
> in a "Hyperthreading system" no physical second CPU" but just two
> register-sets and caches.
>
> So the speed win comes if one process is halted or used, I doubt we can
have
> real
> 45% increase like with a true SMP-System. After what I have read till now,
> Floating-point calculations may be one of the things that get least speed
> improvements from "jackson technology hyperthreading". 25% ?
>
>
> However the Intel approach to help enable multiprocessing in standard
> applications is a good idea and
> I welcome it at any time cause its the way to the PC's of the future..
>
> Also Intel has always had very good SMP-System.
>
> BTW ...
> Some more thinkings ...
> - what do we think about a commandline-switch "-use_SSE" (Intel Streaming
> Extensions) ?
>  :-) is it usable and could it speed up this sort of calculations ?
>
> NVIDIA has just running a study to make Raytracing in Hardware.
> - could we use direct X 9 under windows to get speed improvements in
future
> versions ?
>
> --Theo Gottwald
>
> PS: So long you all work on "the real thing" I've been doing a "so long
> solution".
>      I've put a BETA-Test Version up which supports as many processors as
> anyone may have.
>      In one or in ten PC's.
>      It currently does not support animations and its in Gemran. But maybe
> in a few days ...
>      The link is http://www.it-berater.org/smpov.htm
>
>
>
>
>
>
> "Chris Cason" <new### [at] deletethispovrayorg> schrieb im Newsbeitrag
> news:3d562831@news.povray.org...
> >
> > "Francois Piednoel" <fra### [at] intelcom> wrote in message
> news:3d55aa5d$1@news.povray.org...
> > > we are already working closely with Chris Cason, and we hope to
improve
> > > again the Pentium(R) 4 user experience, via some more improvement.
> >
> > And I would like to take this opportunity to publicly thank Francois for
> his
> > hard work on the P4 optimizations already in 3.5. I am quite looking
> forward
> > to seeing his hyperthreading implementation.
> >
> > -- Chris
> >
> >
>
>

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