High CPU usage in scheduler #2033
Description
With below program, we find that the scheduler shows ~380% CPU usage vs ~200% in runc.
How to test:
$ docker run -it --cpu-period=1000 --cpu-quota=8000 ...
$ gcc -o threads thread.c -lpthread
$ ./threads 1024 100000
#include <stdio.h>
#include <pthread.h>
#include <sys/time.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdint.h>
struct worker_arg {
int seq;
int iterations;
pthread_mutex_t count_lock;
pthread_cond_t count_nonzero;
unsigned count;
};
static void
park(struct worker_arg *arg)
{
pthread_mutex_lock(&arg->count_lock);
while (arg->count == 0)
pthread_cond_wait(&arg->count_nonzero, &arg->count_lock);
arg->count--;
pthread_mutex_unlock(&arg->count_lock);
}
static void
unpark(struct worker_arg *arg)
{
pthread_mutex_lock(&arg->count_lock);
if (arg->count == 0)
pthread_cond_signal(&arg->count_nonzero);
arg->count++;
pthread_mutex_unlock(&arg->count_lock);
}
static void *
worker(void *p)
{
struct worker_arg *arg = (struct worker_arg *)p;
while (arg->iterations--) {
/* do some work */
//printf("%d %d\n", arg->seq, arg->iterations);
park(arg);
}
return NULL;
}
int
main(int argc, char **argv)
{
int i, j, N, M;
void *dummy;
struct worker_arg *args;
pthread_t *tids;
if (argc != 3) {
fprintf(stderr, "Usage: %s <number of threads> <iterations>\n", argv[0]);
exit(1);
}
N = atoi(argv[1]);
M = atoi(argv[2]);
tids = malloc(sizeof(*tids) * N);
args = malloc(sizeof(*args) * N);
for (i = 0; i < N; i++) {
args[i].seq = i;
args[i].iterations = M;
args[i].count = 0;
pthread_mutex_init(&args[i].count_lock, NULL);
pthread_cond_init(&args[i].count_nonzero, NULL);
pthread_create(&tids[i], NULL, worker, &args[i]);
}
for (i = 0; i < M; i++) {
for (j = 0; j < N; j++)
unpark(&args[j]);
}
for (i = 0; i < N; i++)
pthread_join(tids[i], &dummy);
}