Status changed to 'Confirmed' because the bug affects multiple users.
** Changed in: suitesparse (Ubuntu)
Status: New => Confirmed
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https://bugs.launchpad.net/bugs/1843277
Title:
CHOLMOD slows down in parallel
Status in suitesparse package in Ubuntu:
Confirmed
Bug description:
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 running Ubuntu 18.04, everything
up-to-date.
In my research project with a more complex matrix, the slow-down is the
factor 8.
Further info: It is not machine-dependent. It is also confirmed in
Debian 10 on several different machines.
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