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timetctxsw2.c
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timetctxsw2.c
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// Copyright (C) 2010 Benoit Sigoure
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
#include <sched.h>
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <errno.h>
static inline long long unsigned time_ns(struct timespec* const ts) {
if (clock_gettime(CLOCK_REALTIME, ts)) {
exit(1);
}
return ((long long unsigned) ts->tv_sec) * 1000000000LLU
+ (long long unsigned) ts->tv_nsec;
}
static const int iterations = 500000;
static void* thread(void*ctx) {
(void)ctx;
for (int i = 0; i < iterations; i++)
sched_yield();
return NULL;
}
int main(void) {
struct sched_param param;
param.sched_priority = 1;
if (sched_setscheduler(getpid(), SCHED_FIFO, ¶m))
fprintf(stderr, "sched_setscheduler(): %s\n", strerror(errno));
struct timespec ts;
pthread_t thd;
if (pthread_create(&thd, NULL, thread, NULL)) {
return 1;
}
long long unsigned start_ns = time_ns(&ts);
for (int i = 0; i < iterations; i++)
sched_yield();
long long unsigned delta = time_ns(&ts) - start_ns;
const int nswitches = iterations << 2;
printf("%i thread context switches in %lluns (%.1fns/ctxsw)\n",
nswitches, delta, (delta / (float) nswitches));
return 0;
}