clipka <nomail@nomail> wrote:
> A multicore system is basically just a multiprocessor system, with the
> processors placed on a single die to (a) reduce costs, (b) share more
> components among the CPUs (e.g. cache) to reduce synchronization overhead, and
> (c) speed up synchronization of the remaining components by reducing signal
> path lengths.

  Actually shared/non-shared caches can have a big effect and make a
notable difference between multiprocessor and multicore systems.

  Sometimes a shared cache can be beneficial, especially if one single
program runs several threads, all of them sharing the same data. However,
sometimes a shared cache can be detrimental, especially for unrelated
processes which do not share data but must share cache space because
the cores don't have separate caches.

  With POV-Ray I must assume that it benefits from a shared cache, or
at worst it is not hindered by it. (Given that most data POV-Ray 3.7
uses is read-only, it wouldn't make too much of a difference if each
core had its own independent cache.)

> Look again at the figures above:

> 1 core  -> 293 seconds
> 4 cores ->  54 seconds

> Either my math is rusty, or this is a speed gain by more than the number of
> cores...

  How many times was the test run? Was there lot of variation?

  It would be interesting it the test was made with something which takes
significantly longer to render (eg. 15 minutes with 1 core or so.).

-- 
                                                          - Warp

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