Warp <war### [at] tagpovrayorg> wrote:

> >         I just ran the tests on another computer with a Core2 duo and the
> > results are rather interesting:
>
> >         With the same binary as above:
> > Empty loop:       2173ms
> > Kiss64 (int):     7541ms
> > Kiss64 (dbl):    15844ms
> > Alvo (floor):    24778ms
> > Alvo (cast):      8469ms
> > Alvo (tmp+cast):  8473ms
> > Isaac:            7810ms
>
>   One thing I can't understand: Why are the results *significantly* faster
> in my Pentium4 (eg. the Isaac RNG seems to be 10 times faster, which is
> a HUGE difference in speed), even though a Core2 duo should be faster
> than a Pentium4? Something does not compute here.

What's the processor clock of your P4?
What's the typical processor clock of a modern multi-core CPU?

My Windows machine is an old, darn slow 3.4 GHz P4.
My Linux machine is a new, speedy 2.3 GHz AMD Phenom X4.

The modern Multi-Core CPUs win mainly due to...

- optimizations regarding caches, pipelining etc.
- providing multiple cores to run programs on

With a PRNG test suite, however, none of these bring any advantage. There are no
difficult-to-predict branch instructions; virtually no additional data to fetch
into the caches; no parallel threads to distribute the workload; all the CPU
has to do is to braindeadly execute one single thread of pure arithmetic
instructions.

I'm not too much surprised that in this case the bottleneck is sheer GHz power -
the only thing that hasn't been improved at all since the P4 (to the contrary!).

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