This example shows how to profile parallel code using the parallel profiler on workers in a parallel pool.
Create a parallel pool.
numberOfWorkers = 3; pool = parpool(numberOfWorkers);
Starting parallel pool (parpool) using the 'local' profile ... Connected to the parallel pool (number of workers: 3).
Collect parallel profile data by enabling
Run your parallel code. For the purposes of this example, use a simple
parfor loop that iterates over a series of values.
values = [5 12 13 1 12 5]; tic; parfor idx = 1:numel(values) u = rand(values(idx)*3e4,1); out(idx) = max(conv(u,u)); end toc
Elapsed time is 31.228931 seconds.
After the code completes, view the results from the parallel profiler by calling
mpiprofile viewer. This action also stops profile data collection.
The report shows execution time information for each function that runs on the workers. You can explore which functions take the most time in each worker.
Generally, comparing the workers with the minimum and maximum total execution times is useful. To do so, click Compare (max vs. min TotalTime) in the report. In this example, observe that
conv executes multiple times and takes significantly longer in one worker than in the other. This observation suggests that the load might not be distributed evenly across the workers.
If you do not know the workload of each iteration, then a good practice is to randomize the iterations, such as in the following sample code.
values = values(randperm(numel(values)));
If you do know the workload of each iteration in your
parfor loop, then you can use
parforOptions to control the partitioning of iterations into subranges for the workers. For more information, see
In this example, the greater
values(idx) is, the more computationally intensive the iteration is. Create a set of
parfor options to divide the
parfor iterations into subranges of size
2 so that the workload is better distributed.
opts = parforOptions(pool,"RangePartitionMethod","fixed","SubrangeSize",2);
Enable the parallel profiler.
Run the same code as before. To use the
parfor options, pass them to the second input argument of
values = [5 12 13 1 12 5]; tic; parfor (idx = 1:numel(values),opts) u = rand(values(idx)*3e4,1); out(idx) = max(conv(u,u)); end toc
Elapsed time is 21.077027 seconds.
Visualize the parallel profiler results.
In the report, select Compare (max vs. min TotalTime) to compare the workers with the minimum and maximum total execution times. Observe that this time, the multiple executions of
conv take a similar amount of time in all workers. The workload is now better distributed.