Xgboost, max number of cores

Question

I am running XGboost in R on Windows Server 2008 R2.

I have 4 Xeon E7 with 10 cores each. (80 threads total)

I run Xgboost with nthread = 80 but R uses only 40. Does xgboost somehow reduces the number of threads, depending on the Input Data?

Does anyone had similar problems?

Answer 1

i think it doesn't work with the hyperthreading x2 thread

from xgboost site https://github.com/dmlc/xgboost/blob/cb4de521c13f3d2269c20252a393cfd33f4a1ae3/doc/tutorials/external_memory.rst

Performance Note

the parameter nthread should be set to number of real cores Most modern CPU offer hyperthreading, which means you can have a 4 core cpu with 8 threads Set nthread to be 4 for maximum performance in such case