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PnetCDF I/O Benchmark using BTIO Pattern

This software benchmarks the performance of PnetCDF and MPI-IO methods for the I/O pattern used by the NASA's NAS Parallel Benchmarks (NPB) suite (http://www.nas.nasa.gov/publications/npb.html). The evaluation method is strong scaling.

BTIO presents a block-tridiagonal partitioning pattern on a three-dimensional array across a square number of MPI processes. Each process is responsible for multiple Cartesian subsets of the entire data set, whose number increases with the square root of the number of processes participating in the computation. A single global array with an unlimited dimension is created as a netCDF record variable in the output file. The array is of five dimensions and only partitioned among processes along the middle three dimensions. Each record is a subarray of the least significant four dimensions. The number of records to write and read is user adjustable. All records are consecutively written to a shared file in parallel by appending one record after another. The array variable is stored in the file in a canonical, row-major order. To measure the read performance, the global variable is later read back, using the same data partitioning pattern. The size of global array can also be adjusted in the input parameter file 'inputbt.data'. For an illustration of data partitioning pattern, please refer to:

  • Wei-keng Liao. "Design and Evaluation of MPI File Domain Partitioning Methods under Extent-Based File Locking Protocol", in the IEEE Transactions on Parallel and Distributed Systems, 22(2):260-272, February 2011.

To compile:

Edit ./Makefile and change the following 3 variables.

        MPIF90        -- MPI Fortran compiler
        FCFLAGS       -- compile flag
        PNETCDF_DIR   -- path of PnetCDF library (1.4.0 and higher is required)

For example:

        MPIF90      = /usr/bin/mpif90
        FCFLAGS     = -O2
        PNETCDF_DIR = ${HOME}/PnetCDF

Run command make to build the executable, named btio, in the current folder.

To run:

The input parameter file named 'inputbt.data' is required to run the benchmark. An example is provided in the current folder. Users can adjust the following parameters in the file.

        w        : IO mode: w for write, r for read
        IO method: for example, 0 for using MPI collective I/O
        number of time steps
        grid_points(1), grid_points(2), grid_points(3)
        directory name for storing the input and output files

For example, the contents of file inputbt.data are:

        w                  # IO mode: w for write, r for read
        3                  # IO method: 0 for MPI collective IO, 1 for MPI independent IO, 2 for PnetCDF blocking I/O, 3 for PnetCDF nonblocking I/O
        40                 # number of writes/reads
        512 512 512        # grid_points(1), grid_points(2), grid_points(3)
        /scratch2/scratchdirs/wkliao/FS_1M_128

which set

  • (at first line) w to perform write operations only
  • (at second line) the I/O method to use PnetCDF nonblocking APIs
  • (at third line) number of global arrays to write and read
  • (at fourth line) the 3D global array size
  • (at fifth line) the input/output directory name.

Note that btio creates a file named btio.nc in the output directory containing a 5D array variable named var of size NUM_DUMPS x Z x Y x X x FIVE_DBL. The variable's data type is double. The unlimited dimension NUM_DUMPS corresponds to the number of record writes (or reads for read case). Z, Y, and X correspond to grid_points(3), grid_points(2), grid_points(1), respectively. FIVE_DBL is the fifth dimension of size 5, which is not partitioned among processes.

Example command to run an MPI job:

        mpiexec -n 1024 ./btio

or

        mpiexec -n 1024 ./btio inputbt.data

The only optional command-line argument is the input parameter file name. In this example, it is inputbt.data. This argument allows to use a different input file name besides the default inputbt.data.

Example output from the standard out:

    -- BT-IO Benchmark (write operation only) --
    Number of MPI processes  :      1024
    Global array size X      :       512
    Global array size Y      :       512
    Global array size Z      :       512
    Number of I/O iterations :        40
    Total I/O amount         :    204800.00 MiB
    Time in sec              :        41.95
    I/O bandwidth                   4882.00 MiB/s
    ------------------------------------------
    Using Parallel netCDF non-blocking I/O method
    output file path         : /scratch2/scratchdirs/wkliao/FS_1M_128
    file striping count      :       128
    file striping size       :   1048576 bytes

Example metadata of the output file

A single netCDF file named btio.nc will be created once the run completes. To show the file header, use the netCDF utility program ncdump.

% ncdump -h ./btio.nc

netcdf btio {
dimensions:
        FIVE_DBL = 5 ;
        X = 512 ;
        Y = 512 ;
        Z = 512 ;
        NUM_DUMPS = UNLIMITED ; // (40 currently)
variables:
        double var(NUM_DUMPS, Z, Y, X, FIVE_DBL) ;
}

Questions/Comments:

email: wkliao@eecs.northwestern.edu

Copyright (C) 2013, Northwestern University.

See COPYRIGHT notice in top-level directory.