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/*
Check that a thread which yields with pause (rep;nop) makes less
progress against a pure spinner.
*/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
static pthread_mutex_t m_go = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t c_go = PTHREAD_COND_INITIALIZER;
static pthread_cond_t c_running = PTHREAD_COND_INITIALIZER;
static volatile int alive, running;
static int spin;
static int rep_nop;
static void *spinner(void *v)
{
pthread_mutex_lock(&m_go);
while(!alive)
pthread_cond_wait(&c_go, &m_go);
running++;
pthread_cond_signal(&c_running);
pthread_mutex_unlock(&m_go);
while(alive)
spin++;
return 0;
}
static void *rep_nopper(void *v)
{
pthread_mutex_lock(&m_go);
while(!alive)
pthread_cond_wait(&c_go, &m_go);
running++;
pthread_cond_signal(&c_running);
pthread_mutex_unlock(&m_go);
while(alive) {
rep_nop++;
// This gives a hint to a P4, telling it to pause
// (ie. we're in a spin-wait loop)
asm volatile ("rep; nop" : : : "memory");
}
return 0;
}
int main()
{
pthread_t a, b;
pthread_create(&a, NULL, spinner, NULL);
pthread_create(&b, NULL, rep_nopper, NULL);
/* make sure both threads start at the same time */
pthread_mutex_lock(&m_go);
alive = 1;
pthread_cond_broadcast(&c_go);
/* make sure they both get started */
while(running < 2)
pthread_cond_wait(&c_running, &m_go);
pthread_mutex_unlock(&m_go);
sleep(2);
alive = 0;
pthread_join(a, NULL);
pthread_join(b, NULL);
if (0)
printf("spin=%d rep_nop=%d rep_nop:spin ratio: %g\n",
spin, rep_nop, (float)rep_nop / spin);
if (spin > rep_nop)
printf("PASS\n");
else
printf("FAIL spin=%d rep_nop=%d rep_nop:spin ratio: %g\n",
spin, rep_nop, (float)rep_nop / spin);
return 0;
}
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