Timing code Printing Zero Values

[zak100]

Hi,
I am trying to calculate the time for execution of my application. I think its giving me correct elapsed time because this value is not zero. However, some values are zero like:

My total CPU time for parent = 0 ms.
My system CPU time for parent = 0 ms.
My total CPU time for child processes = 0 ms.

My complete code is given below:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <sys/types.h>
#include <sys/times.h>
#include <sys/time.h>
#include <limits.h>
#include <unistd.h>


/* Program Parameters */
#define MAXN 2000  /* Max value of N */
int N;  /* Matrix size i.e rows * cols */
int procs;  /* Number of processors to use */

/* Matrices and vectors */
volatile float A[MAXN][MAXN], B[MAXN], X[MAXN];
/* A * X = B, solve for X */
/* returns a seed for srand based on the time */
unsigned int time_seed() {
  struct timeval t;
  struct timezone tzdummy;

  gettimeofday(&t, &tzdummy);
  return (unsigned int)(t.tv_usec);
}

/* Set the program parameters from the command-line arguments */
void parameters(int argc, char **argv) {
  int submit = 0;  /* = 1 if submission parameters should be used */
  int seed = 0;  /* Random seed */
  char uid[/*L_cuserid + 2*/50]; /*User name */

  /* Read command-line arguments */
  srand(time_seed());  /* Randomize */
  if (argc != 3) {
    if ( argc == 2 && !strcmp(argv[1], "submit") ) {
      /* Use submission parameters */
      submit = 1;
      N = 4;
      procs = 2;
      printf("\nSubmission run for \"%s\".\n", getlogin()/*cuserid(uid)*/ );
      //srand(randm());
    }
    else {
      if (argc == 4) {
	seed = atoi(argv[3]);
	srand(seed);
	printf("Random seed = %i\n", seed);
      }
      else {
	printf("Usage: %s <matrix_dimension> <num_procs> [random seed]\n",
	       argv[0]);
	printf("       %s submit\n", argv[0]);
	exit(0);
      }
    }
  }
  /* Interpret command-line args */
  if (!submit) {
    N = atoi(argv[1]);
    if (N < 1 || N > MAXN) {
      printf("N = %i is out of range.\n", N);
      exit(0);
    }
    procs = atoi(argv[2]);
    if (procs < 1) {
      printf("Warning: Invalid number of processors = %i.  Using 1.\n", procs);
      procs = 1;
    }
   // USE CORES?
     /*if (procs > m_get_numprocs()) {
      printf("Warning: %i processors requested; only %i available.\n",
	     procs, m_get_numprocs());
      procs = m_get_numprocs();
    }*/
  }
/* Print parameters */
  printf("\nMatrix dimension N = %i.\n", N);
  printf("Number of processors = %i.\n", procs);

  /* Set number of processors */
  /*m_set_procs(procs);
    CORES ?
  */
}
/* Initialize A and B (and X to 0.0s) */
void initialize_inputs() {
  int row, col;

  printf("\nInitializing...\n");
  for (col = 0; col < N; col++) {
    for (row = 0; row < N; row++) {
      A[row][col] = (float)rand() / 32768.0;
    }
    B[col] = (float)rand() / 32768.0;
    X[col] = 0.0;
  }
  
}

/* Print input matrices */
void print_inputs() {
  int row, col;

  if (N < 10) {
    printf("\nA =\n\t");
    for (row = 0; row < N; row++) {
      for (col = 0; col < N; col++) {
	printf("%5.2f%s", A[row][col], (col < N-1) ? ", " : ";\n\t");
      }
    }
    printf("\nB = [");
    for (col = 0; col < N; col++) {
      printf("%5.2f%s", B[col], (col < N-1) ? "; " : "]\n");
    }
  }
}


void main(int argc, char **argv) {
  /* Timing variables */
  struct timeval etstart, etstop;  /* Elapsed times using gettimeofday() */
  struct timezone tzdummy;
  clock_t etstart2, etstop2;  /* Elapsed times using times() */
  unsigned long long usecstart, usecstop;
  struct tms cputstart, cputstop;  /* CPU times for my processes */

  /* Process program parameters */
  parameters(argc, argv);

  

  /* Start Clock */
  printf("\nStarting clock.\n");
  gettimeofday(&etstart, &tzdummy);
  etstart2 = times(&cputstart);

 /* Initialize A and B */
  initialize_inputs();

  /* Print input matrices */
  print_inputs();

  /* Stop Clock */
  gettimeofday(&etstop, &tzdummy);
  etstop2 = times(&cputstop);
  printf("Stopped clock.\n");
  usecstart = (unsigned long long)etstart.tv_sec * 1000000 + etstart.tv_usec;
  usecstop = (unsigned long long)etstop.tv_sec * 1000000 + etstop.tv_usec;

  /* Display output */
  
  /* Display timing results */
  printf("\nElapsed time = %g ms.\n",
	 (float)(usecstop - usecstart)/(float)1000);
  /*printf("               (%g ms according to times())\n",
   *       (etstop2 - etstart2) / (float)_CLK_TCK) * 1000);
   */
  printf("(CPU times are accurate to the nearest %g ms)\n",
	 1.0/(float)(sysconf(_SC_CLK_TCK)) * 1000.0);//NEW
  printf("My total CPU time for parent = %g ms.\n",
	 (float)( (cputstop.tms_utime + cputstop.tms_stime) -
		  (cputstart.tms_utime + cputstart.tms_stime) ) /
	 (float)(sysconf(_SC_CLK_TCK)) * 1000);
  printf("My system CPU time for parent = %g ms.\n",
	 (float)(cputstop.tms_stime - cputstart.tms_stime) /
	 (float)(sysconf(_SC_CLK_TCK)) * 1000);
  printf("My total CPU time for child processes = %g ms.\n",
	 (float)( (cputstop.tms_cutime + cputstop.tms_cstime) -
		  (cputstart.tms_cutime + cputstart.tms_cstime) ) /
	 (float)(sysconf(_SC_CLK_TCK)) * 1000);
      /* Contrary to the man pages, this appears not to include the parent */
  printf("--------------------------------------------\n");

}

My complete output is:

Submission run for "zulfi".

Matrix dimension N = 4.
Number of processors = 2.

Starting clock.

Initializing...

A =
41362.46, 17993.23, 39584.68, 60143.39;
43188.59, 16488.19, 40613.91, 40246.41;
27072.91, 24723.83, 50802.55, 59139.54;
25274.54, 52512.21, 7269.44, 26239.78;

B = [35349.72; 54644.97; 64275.91; 47736.07]
Stopped clock.

Elapsed time = 0.172 ms.
(CPU times are accurate to the nearest 10 ms)
My total CPU time for parent = 0 ms.
My system CPU time for parent = 0 ms.
My total CPU time for child processes = 0 ms.

Can somebody please guide me why I am getting zero values in the output?

Zulfi.

[salem c]

1. Fix your warnings.

$ gcc -g -Wall -Wextra main.c
main.c: In function ‘parameters’:
main.c:33:8: warning: unused variable ‘uid’ [-Wunused-variable]
   char uid[/*L_cuserid + 2*/50]; /*User name */
        ^
main.c: At top level:
main.c:122:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
 void main(int argc, char **argv) {
      ^
main.c: In function ‘main’:
main.c:126:21: warning: variable ‘etstop2’ set but not used [-Wunused-but-set-variable]
   clock_t etstart2, etstop2;  /* Elapsed times using times() */
                     ^
main.c:126:11: warning: variable ‘etstart2’ set but not used [-Wunused-but-set-variable]
   clock_t etstart2, etstop2;  /* Elapsed times using times() */
           ^

> Can somebody please guide me why I am getting zero values in the output?
Because to a close approximation, the CPU spent zero time in your code.
The Elapsed time counts everything, like waiting for your terminal to scroll a line, and other "outside of your program delays".

If you want the two to approximate to one another, you need to time WITHOUT all the printf.

$ gdb -q ./a.out
Reading symbols from ./a.out...done.
(gdb) b 161
Breakpoint 1 at 0x400dc6: file main.c, line 161.
(gdb) run submit
Starting program: /home/sc/Documents/a.out submit

Submission run for "(null)".

Matrix dimension N = 4.
Number of processors = 2.

Starting clock.

Initializing...

A =
	45414.91, 30763.74, 13820.80, 12768.55;
	48488.48, 29524.33, 37303.70, 32703.15;
	60592.30, 63970.63, 9712.53, 11859.02;
	45788.96, 43055.27, 31798.37, 56445.63;
	
B = [63451.12; 61307.25; 23064.80; 42820.51]
Stopped clock.

Elapsed time = 0.042 ms.

Breakpoint 1, main (argc=2, argv=0x7fffffffdf38) at main.c:161
161	  printf("(CPU times are accurate to the nearest %g ms)\n",
(gdb) info locals
etstart = {tv_sec = 1552807385, tv_usec = 490306}
etstop = {tv_sec = 1552807385, tv_usec = 490348}
tzdummy = {tz_minuteswest = 0, tz_dsttime = 0}
etstart2 = 1718247374
etstop2 = 1718247374
usecstart = 1552807385490306
usecstop = 1552807385490348
cputstart = {tms_utime = 0, tms_stime = 0, tms_cutime = 0, tms_cstime = 0}
cputstop = {tms_utime = 0, tms_stime = 0, tms_cutime = 0, tms_cstime = 0}
(gdb) p usecstop - usecstart
$1 = 42

The actual time in your program (excluding all the waiting for I/O) was just 42uS.

[zak100]

Hi,
I tried with a debugger but I got following:

gdb -q ./gauss2 10 8 2
Excess command line arguments ignored. (8 ...)
Reading symbols from ./gauss2...(no debugging symbols found)...done.
Attaching to program: /home/zulfi/Ass1PPToSubmit/gauss2, process 10
Could not attach to process. If your uid matches the uid of the target
process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try
again as the root user. For more details, see /etc/sysctl.d/10-ptrace.conf
ptrace: Operation not permitted.
/home/zulfi/Ass1PPToSubmit/10: No such file or directory.
(gdb)

I dont know how to fix this problem. I have to pass the arguments. If possible please guide me.


Zulfi.

[salem c]

The arguments are passed on the run command in gdb, not the command line to gdb

gdb -q ./gauss2
...
(gdb) run 10 8 2

> Reading symbols from ./gauss2...(no debugging symbols found)...done.
Oh, and if you want a meaningful debug experience, pass the -g flag to the compiler when you compile your code.