Documentation/prctl/disable-tsc-on-off-stress-test.c

   1 /*
   2  * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...)
   3  *
   4  * Tests if the control register is updated correctly
   5  * when set with prctl()
   6  *
   7  * Warning: this test will cause a very high load for a few seconds
   8  *
   9  */
  10
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <unistd.h>
  14 #include <signal.h>
  15 #include <inttypes.h>
  16 #include <wait.h>
  17
  18
  19 #include <sys/prctl.h>
  20 #include <linux/prctl.h>
  21
  22 /* Get/set the process' ability to use the timestamp counter instruction */
  23 #ifndef PR_GET_TSC
  24 #define PR_GET_TSC 25
  25 #define PR_SET_TSC 26
  26 # define PR_TSC_ENABLE          1   /* allow the use of the timestamp counter */
  27 # define PR_TSC_SIGSEGV         2   /* throw a SIGSEGV instead of reading the TSC */
  28 #endif
  29
  30 /* snippet from wikipedia :-) */
  31
  32 uint64_t rdtsc() {
  33 uint32_t lo, hi;
  34 /* We cannot use "=A", since this would use %rax on x86_64 */
  35 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
  36 return (uint64_t)hi << 32 | lo;
  37 }
  38
  39 int should_segv = 0;
  40
  41 void sigsegv_cb(int sig)
  42 {
  43         if (!should_segv)
  44         {
  45                 fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
  46                 exit(0);
  47         }
  48         if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
  49         {
  50                 perror("prctl");
  51                 exit(0);
  52         }
  53         should_segv = 0;
  54
  55         rdtsc();
  56 }
  57
  58 void task(void)
  59 {
  60         signal(SIGSEGV, sigsegv_cb);
  61         alarm(10);
  62         for(;;)
  63         {
  64                 rdtsc();
  65                 if (should_segv)
  66                 {
  67                         fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
  68                         exit(0);
  69                 }
  70                 if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
  71                 {
  72                         perror("prctl");
  73                         exit(0);
  74                 }
  75                 should_segv = 1;
  76         }
  77 }
  78
  79
  80 int main(int argc, char **argv)
  81 {
  82         int n_tasks = 100, i;
  83
  84         fprintf(stderr, "[No further output means we're allright]\n");
  85
  86         for (i=0; i<n_tasks; i++)
  87                 if (fork() == 0)
  88                         task();
  89
  90         for (i=0; i<n_tasks; i++)
  91                 wait(NULL);
  92
  93         exit(0);
  94 }
  95