tests xdr & native C binary I/O performance for vector and element-wise access.

test_xdr.C

// g++ -O2 -o test_xdr test_xdr.C ; time ./test_xdr

#include <iostream>
#include <vector>
#include <rpc/rpc.h>
#include <ctime>
#include <sys/time.h>



int main (int argc, char **argv)

{
#define BUFSIZE 1024*1000*100

  std::vector<double> data(BUFSIZE);
  timeval tstart, tstop;

  // write one big vector, C
  {
    FILE  *fp = fopen("test0.dat", "w");

    gettimeofday (&tstart, NULL);

    fwrite (&data[0],
	    sizeof(double),
	    data.size(),
	    fp);

    fflush (fp);
    fclose (fp);

    gettimeofday (&tstop, NULL);

    const double elapsed_time = (static_cast<double>(tstop.tv_sec  - tstart.tv_sec) +
				 static_cast<double>(tstop.tv_usec - tstart.tv_usec)*1.e-6);

    std::cout << "C fwrite:\n";
    std::cout << "Wrote " << BUFSIZE*sizeof(double)/1.e6
	      << "MB in " << elapsed_time << " seconds ("
	      << (BUFSIZE*sizeof(double)/1.e6/elapsed_time) << ") MB/sec.\n";
  }


  // write each element individually, XDR
  {
    FILE  *fp = fopen("test1.dat", "w");

    gettimeofday (&tstart, NULL);

    for (unsigned int cnt=0; cnt<data.size(); cnt++)
      {
	fwrite (&data[cnt],
		sizeof(double),
		1,
		fp);
      }

    fflush (fp);
    fclose (fp);

    gettimeofday (&tstop, NULL);

    const double elapsed_time = (static_cast<double>(tstop.tv_sec  - tstart.tv_sec) +
				 static_cast<double>(tstop.tv_usec - tstart.tv_usec)*1.e-6);

    std::cout << "C fwrite:\n";
    std::cout << "Wrote " << BUFSIZE*sizeof(double)/1.e6
	      << "MB in " << elapsed_time << " seconds ("
	      << (BUFSIZE*sizeof(double)/1.e6/elapsed_time) << ") MB/sec.\n";
  }

  // write one big vector, XDR
  {
    XDR *xdrs = new XDR;
    FILE  *fp = fopen("test1.xdr", "w");

    xdrstdio_create (xdrs, fp, XDR_ENCODE);

    gettimeofday (&tstart, NULL);

    xdr_vector(xdrs,
	       (char*) &data[0],
	       data.size(),
	       sizeof(double),
	       (xdrproc_t) xdr_double);

    xdr_destroy (xdrs);
    delete xdrs;
    fflush (fp);
    fclose (fp);

    gettimeofday (&tstop, NULL);

    const double elapsed_time = (static_cast<double>(tstop.tv_sec  - tstart.tv_sec) +
				 static_cast<double>(tstop.tv_usec - tstart.tv_usec)*1.e-6);

    std::cout << "XDR write:\n";
    std::cout << "Wrote " << BUFSIZE*sizeof(double)/1.e6
	      << "MB in " << elapsed_time << " seconds ("
	      << (BUFSIZE*sizeof(double)/1.e6/elapsed_time) << ") MB/sec.\n";
  }


  // write each element individually, XDR
  {
    XDR *xdrs = new XDR;
    FILE  *fp = fopen("test2.xdr", "w");

    xdrstdio_create (xdrs, fp, XDR_ENCODE);

    gettimeofday (&tstart, NULL);

    for (unsigned int cnt=0; cnt<data.size(); cnt++)
      {
	xdr_vector(xdrs,
		   (char*) &data[cnt],
		   1,
		   sizeof(double),
		   (xdrproc_t) xdr_double);
      }

    xdr_destroy (xdrs);
    delete xdrs;
    fflush (fp);
    fclose (fp);

    gettimeofday (&tstop, NULL);

    const double elapsed_time = (static_cast<double>(tstop.tv_sec  - tstart.tv_sec) +
				 static_cast<double>(tstop.tv_usec - tstart.tv_usec)*1.e-6);

    std::cout << "XDR write:\n";
    std::cout << "Wrote " << BUFSIZE*sizeof(double)/1.e6
	      << "MB in " << elapsed_time << " seconds ("
	      << (BUFSIZE*sizeof(double)/1.e6/elapsed_time) << ") MB/sec.\n";
  }

return 0;
}