Description
The purpose of this assignment is to acquire hands-on experience on the scalability analysis of a
parallel program — one of the key skills you learn in this class. We use a simple application that
utilizes the function you have written for assignment 2, where the purpose was to:
(i) Convince ourselves that MPI_Send() and MPI_Recv() are sufficient to build any parallel
programs, using global reduction as a concrete example.
(ii) Perform a unit software test of the global_sum() function used in this assignment.
Part I: Programming
Write a message passing interface (MPI) program, global_pi.c, to compute the value of p
based on the lecture note on “Parallel Computation of Pi” and using the global_sum() function
you have implemented and unit-tested in assignment 2. Please also utilize the serial program
pi.c (which computes the value of �) in the assignment 3 package.
(Assignment)
1. Submit the source code of global_pi.c.
(Note)
• Insert MPI_Wtime() function (which takes no argument and returns the wall-clock time in
seconds as double) to measure the running time of the program.
Part II: Scalability
In this assignment, we measure the scalability of global_pi.c.
(Assignment)
2. (Fixed problem-size scaling) Run your global_pi.c with a fixed number of quadrature
points, NBIN = 109
, while varying the number of compute nodes = 1, 2 and 4 with processor
per node to be 1 (i.e., the number of processors P = 1, 2 and 4). Plot the fixed problem-size
parallel efficiency as a function of P. Submit the plot.
3. (Isogranular scaling) In this scalability test, we consider a constant number of quadrature
points, NBIN/P = 109
, per processor for P = 1, 2 and 4. To do this, we slightly modify
global_pi.c by defining
#define NPERP 1000000000 /* Number of quadrature points per processor */
long long NBIN;
and determining the total number of quadrature points as
NBIN = (long long)NPERP*nprocs;
Run the resulting program global_pi_iso.c, and plot the isogranular parallel efficiency as
a function of P. Submit the plot.
(Note)
• Please perform the entire scaling tests in a single batch job to minimize measurement
fluctuations, using the Slurm script, global_pi.sl, in the assignment 3 package.
