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