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34 #include <sys/types.h>
47 #define CAN_USE_ALARMS
56 /* Fifo: Verify that fifo and round-robin scheduling seem to work.
59 * 1. That sched_rr_get_interval seems to work;
60 * 2. That FIFO scheduling doesn't seeem to be round-robin;
61 * 3. That round-robin scheduling seems to work.
65 static void tidyup(void)
72 tvsub(const struct timeval *a, const struct timeval *b)
77 sdiff = a->tv_sec - b->tv_sec;
78 udiff = a->tv_usec - b->tv_usec;
80 return (double)(sdiff * 1000000 + udiff) / 1e6;
83 int fifo(int argc, char *argv[])
86 volatile long *p, pid;
88 struct sched_param fifo_param;
89 struct timespec interval;
91 struct timeval ranat[MAX_RANAT];
94 static struct itimerval itimerval;
97 /* What is the round robin interval?
100 if (sched_rr_get_interval(0, &interval) == -1) {
101 perror("sched_rr_get_interval");
105 #ifdef CAN_USE_ALARMS
106 signal(SIGALRM, tick);
109 fifo_param.sched_priority = 1;
111 p = (long *)mmap(0, sizeof(*p),
112 PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);
119 if (sched_setscheduler(0, SCHED_FIFO, &fifo_param) == -1)
121 perror("sched_setscheduler");
127 if ((child = fork()) == 0)
129 /* Child process. Just keep setting the pointer to our
130 * PID. The parent will kill us when it wants to.
145 #ifdef CAN_USE_ALARMS
146 /* Set an alarm for 250 times the round-robin interval.
147 * Then we will verify that a similar priority process
148 * will not run when we are using the FIFO scheduler.
150 itimerval.it_value.tv_usec = interval.tv_nsec / (1000 / 250);
152 itimerval.it_value.tv_sec = itimerval.it_value.tv_usec / 1000000;
153 itimerval.it_value.tv_usec %= 1000000;
156 if (setitimer(ITIMER_REAL, &itimerval, 0) == -1) {
163 gettimeofday(ranat, 0);
165 while (!ticked && i < MAX_RANAT)
167 gettimeofday(ranat + i, 0);
177 "SCHED_FIFO had erroneous context switches:\n");
178 for (j = 1; j < i; j++) {
179 fprintf(stderr, "%d %g\n", j,
180 tvsub(ranat + j, ranat + j - 1));
185 /* Switch to the round robin scheduler and the child
186 * should run within twice the interval.
188 if (sched_setscheduler(child, SCHED_RR, &fifo_param) == -1 ||
189 sched_setscheduler(0, SCHED_RR, &fifo_param) == -1)
191 perror("sched_setscheduler");
199 #ifdef CAN_USE_ALARMS
201 /* Now we do want to see it run. But only set
202 * the alarm for twice the interval:
204 itimerval.it_value.tv_usec = interval.tv_nsec / 500;
206 if (setitimer(ITIMER_REAL, &itimerval, 0) == -1) {
212 for (i = 0; !ticked; i++)
219 fprintf(stderr,"Child never ran when it should have.\n");
225 #ifdef STANDALONE_TESTS
226 int main(int argc, char *argv[]) { return fifo(argc, argv); }