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 static uint64_t rdtsc(void)
  33 {
  34 uint32_t lo, hi;
  35 /* We cannot use "=A", since this would use %rax on x86_64 */
  36 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
  37 return (uint64_t)hi << 32 | lo;
  38 }
  39
  40 int should_segv = 0;
  41
  42 static void sigsegv_cb(int sig)
  43 {
  44         if (!should_segv)
  45         {
  46                 fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
  47                 exit(0);
  48         }
  49         if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
  50         {
  51                 perror("prctl");
  52                 exit(0);
  53         }
  54         should_segv = 0;
  55
  56         rdtsc();
  57 }
  58
  59 static void task(void)
  60 {
  61         signal(SIGSEGV, sigsegv_cb);
  62         alarm(10);
  63         for(;;)
  64         {
  65                 rdtsc();
  66                 if (should_segv)
  67                 {
  68                         fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
  69                         exit(0);
  70                 }
  71                 if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
  72                 {
  73                         perror("prctl");
  74                         exit(0);
  75                 }
  76                 should_segv = 1;
  77         }
  78 }
  79
  80
  81 int main(void)
  82 {
  83         int n_tasks = 100, i;
  84
  85         fprintf(stderr, "[No further output means we're allright]\n");
  86
  87         for (i=0; i<n_tasks; i++)
  88                 if (fork() == 0)
  89                         task();
  90
  91         for (i=0; i<n_tasks; i++)
  92                 wait(NULL);
  93
  94         exit(0);
  95 }
  96