How to check OpenMP usage in python graph-tool

Question

I am using python graph-tool for this algorithm in order to find min-cut in a large graph. My algorithm needs several calls to this function, and it seems to be the bottleneck. So I want to ensure if it is being run as efficiently as it could be i.e. using OpenMP.

However, on changing number of threads using openmp_set_num_threads(n), I get the same time for different number of threads viz. 2, 24 and 128.

Is there a way to check if OpenMP is being used by the graph-tool? I have checked the number of threads using openmp_get_num_threads and it is correct. Also how to enable OpenMP in case it is not being used by the graph-tool?

Alternatively, is there a way to check if some particular function of graph-tool, boykov_kolmogorov_max_flow in our case, uses OpenMP?

How do you use openMP with Python? There is no direct support, see here — supercheval
– supercheval, Commented Jul 29, 2018 at 10:34
@Imontigny I am using the python library graph-tool which is implemented in C++, and thus can use OpenMP. At least this is what they claim they do. — arpanmangal
– arpanmangal, Commented Jul 29, 2018 at 14:08
Ok, can you print the output of graph_tool.openmp_enabled() and graph_tool.openmp_get_num_threads()? — supercheval
– supercheval, Commented Jul 29, 2018 at 17:18
True and correct number of threads respectively. The problem is that the function call to boykov_kolmogorov_max_flow takes the same time for different num_threads. — arpanmangal
– arpanmangal, Commented Jul 29, 2018 at 17:44
Ok, in the graph-tool source code they include <boost/graph/boykov_kolmogorov_max_flow.hpp> and I don't see any openMP pragma in the corresponding file here. It seems that this algorithm is not implemented in parallel. Only a part of graph-tool is parallelized using openMP, I found some omp pragma for pagerank for example. (You can do "grep -wr omp *" in the source folder of graph-tool) — supercheval
– supercheval, Commented Jul 29, 2018 at 20:45

Suuuehgi · Accepted Answer · 2021-10-21 12:45:16Z

0

Meanwhile there is a function for that:

> import graph_tool as gt
> gt.openmp_enabled()
True

Return True if OpenMP was enabled during compilation.

answered Oct 21, 2021 at 12:45

Suuuehgi

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