Example 2 Example 4 Back to GPTL home page

Example 3: GPTLsummary

This hybrid OpenMP/MPI code demonstrates the use of summary routine GPTLpr_summary(). It simulates variable work load by sleeping some amount of time depending on rank and thread number. Here we show only the output--the code is available in tests/global.c. Since only 2 threads were involved, the code was modified from the committed version to sleep some number seconds rather than milliseconds.

Compile and link, then run with 2 threads and 8 MPI tasks. In this example we modified the sleep time to be seconds rather than milliseconds to make the output more easily understood: 

% cd tests
% make global  
% env OMP_NUM_THREADS=2 mpiexec -n 8 ./global
Output file timing.summary was created by a call to GPTLpr_summary(MPI_COMM_WORLD).

timing.summary: 


Total ranks in communicator=8
nthreads on rank 0=2
'N' used for mean, std. dev. calcs.: 'ncalls'/'nthreads'
'ncalls': number of times the region was invoked across tasks and threads.
'nranks': number of ranks which invoked the region.
mean, std. dev: computed using per-rank max time across all threads on each rank
wallmax and wallmin: max, min time across tasks and threads.

name                  ncalls nranks mean_time   std_dev   wallmax (rank  thread)   wallmin (rank  thread)
total                      8      8     7.376     3.021     9.001 (     1     0)     2.001 (     7     0)
nranks-iam+mythread       16      8     5.500     2.449     9.000 (     0     1)     1.000 (     7     0)
1-5_iam                    5      5     3.000     1.581     5.000 (     5     0)     1.000 (     1     0)
In this example iam is the MPI rank and mythread is the thread number. The output shows that sleeping nranks-iam+mythread has a max time of 9 seconds on rank 0, thread 1, an a min time of 1 second on rank 7 thread 0. Mean and standard deviation stats are also printed. The other region, 1-5_iam, is not threaded and only MPI ranks 1 through 5 participate. Max time is on the highest rank participating (5 seconds on rank 5), and min time is on the lowest rank participating (1 second on rank 1).
Example 2 Example 4 Back to GPTL home page