HPC UNITe

MPI4py ping-pong demonstrates point-to-point communication between rank 0 (master) and rank 1 (worker). Rank 0 sends increasingly larger messages to rank 1, which echoes them back; timing measures bandwidth.

#!/usr/bin/env python3 from mpi4py import MPI import numpy as np import sys

comm = MPI.COMM_WORLD rank = comm.Get_rank() size = comm.Get_size()

if size != 2:

  if rank == 0:
      print("Need exactly 2 processes!")
  sys.exit(1)

partner = 1 - rank

nrounds = 100 msg_sizes = [1, 8, 64, 512, 1024, 4096, 16384, 65536, 262144]

for nbytes in msg_sizes:

  nelems = max(1, nbytes // np.dtype(np.uint8).itemsize)

  sendbuf = np.zeros(nelems, dtype=np.uint8)
  recvbuf = np.empty(nelems, dtype=np.uint8)

  comm.Barrier()

  t0 = MPI.Wtime()

  for i in range(nrounds):
      if rank == 0:
          comm.Send(sendbuf, dest=partner, tag=100)
          comm.Recv(recvbuf, source=partner, tag=200)
      else:
          comm.Recv(recvbuf, source=partner, tag=100)
          comm.Send(recvbuf, dest=partner, tag=200)

  t1 = MPI.Wtime()

  if rank == 0:
      total_time = t1 - t0
      avg_rtt = total_time / nrounds
      latency_us = (avg_rtt / 2.0) * 1.0e6
      bandwidth_mb_s = nbytes / latency_us

      print(
          f"size={nbytes:8d} bytes | "
          f"RTT={avg_rtt*1.0e6:10.2f} us | "
          f"latency={latency_us:10.2f} us | "
          f"bandwidth={bandwidth_mb_s:10.2f} MB/s"
      )

if rank == 0:

  print("Ping-pong benchmark completed.")

</code>