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Documentation / prctl / disable-tsc-ctxt-sw-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	 * 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	}
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