r - Xgboost, max number of cores -

i running xgboost in r on windows server 2008 r2.

i have 4 xeon e7 10 cores each. (80 threads total)

i run xgboost nthread = 80 r uses 40. xgboost somehow reduces number of threads, depending on input data?

does had similar problems?

i think doesn't work hyperthreading x2 thread

from xgboost site https://github.com/dmlc/xgboost/blob/master/doc/how_to/external_memory.md

performance note

the parameter nthread should set number of real cores modern cpu offer hyperthreading, means can have 4 core cpu 8 threads set nthread 4 maximum performance in such case