linux/Documentation/prctl/disable-tsc-ctxt-sw-stress-test.c
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   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
  30uint64_t rdtsc() {
  31uint32_t lo, hi;
  32/* We cannot use "=A", since this would use %rax on x86_64 */
  33__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
  34return (uint64_t)hi << 32 | lo;
  35}
  36
  37void sigsegv_expect(int sig)
  38{
  39        /* */
  40}
  41
  42void 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
  57void sigsegv_fail(int sig)
  58{
  59        fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
  60        exit(0);
  61}
  62
  63void 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
  76int 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
  97
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