Why lower active CPU cores?

[ngo]

Hello,
ok I researched a lot here in the forum. And so far I know building the dense cloud is the only part which uses the GPU, all the other parts are based on the CPU.

Next thing I read activating all OpenCL devices in the preferences tab for the dense cloud part and
(here comes the part I do not understand) lowering the active CPUs.

So why do I have to reduce the active CPUs for faster results. Is there no priority system that can decide how many GPU power is there and uses this first ?

Is there a general rule for the settings ? Or do I have to try it individually with different settings ?

-All Cores, No GPU
-GPU and all cores
-GPU and half the cores
GPU no cores

etc. and then compare the building dense cloud times.

Thanks in advanced
/i

[ngo]

Just read,

"lower for each GPU device in the list one CPU core"

So one GPU card active means lower an 8 core to 7 of 8.
And two GPU cards checked active. CPU slider will be set to 6/8.
Guess that?s the general rule of thumb.

Would be still interested in more insides behind that, why we have to lower the cores for GPU devices.

Thanks.

[Alexey Pasumansky]

http://www.agisoft.ru/forum/index.php?topic=394
http://www.agisoft.ru/forum/index.php?topic=2322
http://www.agisoft.ru/forum/index.php?topic=1868.msg14368#msg14368

[ngo]

thank you, helps a lot.