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 static uint64_t rdtsc(void)
  31 {
  32 uint32_t lo, hi;
  33 /* We cannot use "=A", since this would use %rax on x86_64 */
  34 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
  35 return (uint64_t)hi << 32 | lo;
  36 }
  37
  38 static void sigsegv_expect(int sig)
  39 {
  40         /* */
  41 }
  42
  43 static void segvtask(void)
  44 {
  45         if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
  46         {
  47                 perror("prctl");
  48                 exit(0);
  49         }
  50         signal(SIGSEGV, sigsegv_expect);
  51         alarm(10);
  52         rdtsc();
  53         fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
  54         exit(0);
  55 }
  56
  57
  58 static void sigsegv_fail(int sig)
  59 {
  60         fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
  61         exit(0);
  62 }
  63
  64 static void rdtsctask(void)
  65 {
  66         if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
  67         {
  68                 perror("prctl");
  69                 exit(0);
  70         }
  71         signal(SIGSEGV, sigsegv_fail);
  72         alarm(10);
  73         for(;;) rdtsc();
  74 }
  75
  76
  77 int main(void)
  78 {
  79         int n_tasks = 100, i;
  80
  81         fprintf(stderr, "[No further output means we're allright]\n");
  82
  83         for (i=0; i<n_tasks; i++)
  84                 if (fork() == 0)
  85                 {
  86                         if (i & 1)
  87                                 segvtask();
  88                         else
  89                                 rdtsctask();
  90                 }
  91
  92         for (i=0; i<n_tasks; i++)
  93                 wait(NULL);
  94
  95         exit(0);
  96 }
  97