ADACS:-Scaling-and-Profiling-notes.md

@@ -121,9 +121,15 @@ To start this script (e.g. saved as `pbilby.py`) as a Slurm job, simply call `py
 mpirun python pbilby.py outdir/data/GW150914_data_dump.pickle --nact 10 --min-eff 3.0 --label GW150914_0 --outdir outdir/result --sampling-seed 1234
 ```
 
+To perform manual MPI timing (hardcoded into the modified Schwimmbad library in the ADACS branch), add the argument `--mpi-timing 1`, which will give a printout at the end of the run in the log file. To record MPI timings at regular 60 seconds intervals, add `--mpi-timing-interval 60`. 
+
+Note: The MPI timing printout at the end of the run is a sum of all worker tasks, while the periodic timing intervals are only the timings for **one** worker task. This is to prevent necessary MPI communication during the run.
+
+Using excessively short intervals will result in large overheads. The timing results for each interval are saved in a JSON file `mpi_worker_timing.json` at the end of the run.
+
 ## Modifications to the Schwimmbad library
 
-There is some misunderstanding of how the library should be called. The Schwimmbad documentation itself contains incorrect instructions.
+There is some misunderstanding of how the library should be called in the original implementation. The Schwimmbad documentation itself contains incorrect instructions.
 
 The lines of code for the worker tasks
 ```