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Documentation / prctl / disable-tsc-on-off-stress-test.c




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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 EST.

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