none/tests/x86/yield.c

   1 /*
   2    Check that a thread which yields with pause (rep;nop) makes less
   3    progress against a pure spinner.
   4  */
   5 #include <pthread.h>
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <unistd.h>
   9
  10 static pthread_mutex_t m_go = PTHREAD_MUTEX_INITIALIZER;
  11 static pthread_cond_t c_go = PTHREAD_COND_INITIALIZER;
  12 static pthread_cond_t c_running = PTHREAD_COND_INITIALIZER;
  13
  14 static volatile int alive, running;
  15
  16 static int spin;
  17 static int rep_nop;
  18
  19 static void *spinner(void *v)
  20 {
  21         pthread_mutex_lock(&m_go);
  22         while(!alive)
  23                 pthread_cond_wait(&c_go, &m_go);
  24         running++;
  25         pthread_cond_signal(&c_running);
  26         pthread_mutex_unlock(&m_go);
  27
  28         while(alive)
  29                 spin++;
  30
  31         return 0;
  32 }
  33
  34 static void *rep_nopper(void *v)
  35 {
  36         pthread_mutex_lock(&m_go);
  37         while(!alive)
  38                 pthread_cond_wait(&c_go, &m_go);
  39         running++;
  40         pthread_cond_signal(&c_running);
  41         pthread_mutex_unlock(&m_go);
  42
  43         while(alive) {
  44                 rep_nop++;
  45                 // This gives a hint to a P4, telling it to pause
  46                 // (ie. we're in a spin-wait loop)
  47                 asm volatile ("rep; nop" : : : "memory");
  48         }
  49
  50         return 0;
  51 }
  52
  53 int main()
  54 {
  55         pthread_t a, b;
  56
  57         pthread_create(&a, NULL, spinner, NULL);
  58         pthread_create(&b, NULL, rep_nopper, NULL);
  59
  60         /* make sure both threads start at the same time */
  61         pthread_mutex_lock(&m_go);
  62         alive = 1;
  63         pthread_cond_broadcast(&c_go);
  64
  65         /* make sure they both get started */
  66         while(running < 2)
  67                 pthread_cond_wait(&c_running, &m_go);
  68         pthread_mutex_unlock(&m_go);
  69
  70         sleep(2);
  71
  72         alive = 0;
  73         pthread_join(a, NULL);
  74         pthread_join(b, NULL);
  75
  76         if (0)
  77                 printf("spin=%d rep_nop=%d rep_nop:spin ratio: %g\n",
  78                        spin, rep_nop, (float)rep_nop / spin);
  79
  80         if (spin > rep_nop)
  81                 printf("PASS\n");
  82         else
  83                 printf("FAIL spin=%d rep_nop=%d rep_nop:spin ratio: %g\n",
  84                        spin, rep_nop, (float)rep_nop / spin);
  85
  86         return 0;
  87 }