wisemaj schrieb:

> Thanks for the input.  Not sure exactly how they do this, but Intel claims a
> capacity of 8 (simultaneous?) threads for the I7 processor even though it's
> described as "Quad-Core".  Windows Task Monitor shows 8 CPU's and all of them
> peg at 100% during the benchmark. Would that change your 3 to 3.5 speedup factor
> estimate?

What you see there is "hyperthreading" - the capability of each 
individual core to have a certain number of tasks assigned at once (in 
this case two), and essentially switch back and forth between these 
whenever one of them falls idle, e.g. when waiting for data to be 
fetched from main memory into the processor cache. From the OS point of 
view, this is easiest handled by treating each core as two individual ones.

I never examined the effect of this on rendering time before, but the 
figures from a scene I'm currently working on might give an impression 
(run on an i7 machine):

- Restricted to 4 threads:
667 seconds wall-clock time, for a CPU-to-wall-clock ratio of 3.88

- With full 8 threads:
443 seconds wall-clock time, for a CPU-to-wall-clock ratio of 6.99

So yes, there's a significant effect to be seen there.

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