LXR linux/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
  30static uint64_t rdtsc(void)
  31{
  32uint32_t lo, hi;
  33/* We cannot use "=A", since this would use %rax on x86_64 */
  34__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
  35return (uint64_t)hi << 32 | lo;
  36}
  37
  38static void sigsegv_expect(int sig)
  39{
  40        /* */
  41}
  42
  43static 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
  58static void sigsegv_fail(int sig)
  59{
  60        fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
  61        exit(0);
  62}
  63
  64static 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
  77int main(int argc, char **argv)
  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
  98