tests/test-progs/mwait/mwait.c

   1 // author: Marc Orr
   2
   3 #include <pthread.h>
   4 #include <stdio.h>
   5 #include <stdlib.h>
   6
   7 #define NUM_TRIES   1000
   8
   9 // Make sure that flags and wait sit in different cache lines
  10 volatile int flags[10];
  11 volatile int wait[10];
  12
  13 pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
  14
  15 void *DoWork1(void *threadid)
  16 {
  17     flags[0] = flags[0] + 1;
  18     wait[0] = 0;
  19     pthread_exit(0);
  20 }
  21
  22 void *DoWork2(void *threadid)
  23 {
  24     pthread_mutex_lock (&mutex);
  25     flags[0] = flags[0] + 1;
  26     pthread_mutex_unlock (&mutex);
  27     pthread_exit(0);
  28 }
  29
  30 ////////////////////////////////////////////////////////////////////////////////
  31 // Program main
  32 ////////////////////////////////////////////////////////////////////////////////
  33 int main( int argc, char** argv)
  34 {
  35     // stuff for thread
  36     pthread_t threads[1];
  37
  38     // initialize global variables
  39     flags[0] = 0;
  40     wait[0] = 1;
  41
  42     // monitor (via gcc intrinsic)
  43     __builtin_ia32_monitor ((void *)&flags, 0, 0);
  44
  45     // invalidate flags in this cpu's cache
  46     pthread_create(&threads[0], NULL, DoWork1, NULL);
  47     while (wait[0]);
  48
  49     // launch thread to invalidate address being monitored
  50     pthread_create(&threads[0], NULL, DoWork2, NULL);
  51
  52     // wait for other thread to modify flags
  53     int mwait_cnt = 0;
  54     do {
  55         pthread_mutex_lock (&mutex);
  56         if (flags[0] != 2) {
  57             pthread_mutex_unlock (&mutex);
  58             __builtin_ia32_mwait(0, 0);
  59         } else {
  60             pthread_mutex_unlock (&mutex);
  61         }
  62         mwait_cnt++;
  63     } while (flags[0] != 2 && mwait_cnt < NUM_TRIES);
  64
  65     // test may hang if mwait is not working
  66     if (flags[0]==2) {
  67         printf("mwait regression PASSED, flags[0] = %d\n", flags[0]);
  68     } else {
  69         printf("mwait regression FAILED, flags[0] = %d\n", flags[0]);
  70     }
  71
  72     return 0;
  73 }