Comment 0 for bug 1843277

If I run a simple CHOLMOD C++ program, I noticed that it takes more time running in parallel than single threaded. For the attached program file I did

g++ -o main main.cpp /usr/lib/x86_64-linux-gnu/libcholmod.so

time ./main
-> real 2m21,367s user 11m30,913s sys 5m11,448s

(now I force it to be single threaded)
time OPENBLAS_NUM_THREADS=1 OMP_THREAD_LIMIT=1 ./main
-> real 0m49,684s user 0m48,922s sys 0m0,760s

Notice the huge "sys" time consumption in parallel run.

I have a 4 core / 8 thread Intel CPU.
In my research project with a more complex matrix, the slow-down is the factor 8.