[R-pkg-devel] parallel computing slower than sequential computing

[Ivan Krylov]

On Mon, 29 Apr 2019 23:44:42 +0000
"Wang, Zhu" <wangz1 using uthscsa.edu> wrote:

> sessionInfo()  
> R version 3.5.2 (2018-12-20)
> Platform: x86_64-pc-linux-gnu (64-bit)
> Running under: Ubuntu 18.04.2 LTS

Which BLAS implementation do you use? One popular implementation,
OpenBLAS, spawns multiple threads to do some operations faster; the
threads can compete against each other for CPU resources if resulting
number of processes * threads per process is more than what CPU can
handle.

How many CPU cores does your system have? Does this include SMT (also
known as hyper-threading on Intel processors)? While some problems
benefit from processor pipeline being able to fetch from multiple
threads at the same time, for others it's more of a bottleneck.

It may help to decrease the n.cores parameter.

-- 
Best regards,
Ivan