Checking scheduler behavior

bench-scheduler.c

/*

  gcc -O0 scheduler.c -o scheduler-read -DREAD

  or

  gcc -O0 scheduler.c -o scheduler-read -DYIELD

 */


#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sched.h>

#define NCHILDS 8
#define SZ 100*4096

void uselesschild(int n, int useless)
{
        char *s = malloc(SZ);
        unsigned int i = 0;

        if (!s)
        {
                perror("malloc() failed\n");
                exit(1);
        }

        memset(s, 0, SZ);

        while (i < SZ-1)
        {
                s[i++] = 'A' + n;
                putchar('A' + n);
                fflush(stdout);
                if (useless)
#ifdef READ
                        read(0, 0, 0);
#endif
#ifdef YIELD
                        sched_yield();
#endif
        }

        s[SZ-1] = '\x00';
}

int main(void)
{
        pid_t child[NCHILDS], pid;
        unsigned int i;
        cpu_set_t cpus;
        
        CPU_ZERO(&cpus);
        CPU_SET(0, &cpus);
        sched_setaffinity(0, sizeof cpus, &cpus);
        
        for (i = 0 ; i < NCHILDS/2; i++)
        {
                child[i] = pid = fork();
                if (pid == -1)
                {
                        perror("fork failed");
                        exit(1);
                }

                if (pid == 0)
                {
                        uselesschild(i, i %2);
                        exit(0);
                }
        }


        while (waitpid(-1, &i, 0) != -1);
}

/* Local Variables: */
/* c-default-style: k&r */
/* End: */

grapher.py

#! /usr/bin/env python

'''

$ ./bench-scheduler-yield | python grapher.py
$ geeqie out.png

'''


import fileinput
import random
from PIL import Image, ImageDraw

img = Image.new('RGBA', (12000, 100))
draw = ImageDraw.Draw(img)

x=0
y=0
height=100
prev='0'
occur=0
colors={}

for line in fileinput.input():
    for c in line:
        if c != prev:
            width = 1 + ((occur+1) / 1200) * 100
            occur=0
            colors[c] = colors.get(c, (random.randint(0, 255), random.randint(0, 255), random.randint(0, 255)))
            draw.rectangle([x, y, x+width, y+height], fill=colors[c])
            x += width
        else:
            occur += 1
        prev = c

img.save('out.png')