1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* |
3 | * Test null syscall performance |
4 | * |
5 | * Copyright (C) 2009-2015 Anton Blanchard, IBM |
6 | */ |
7 | |
8 | #define NR_LOOPS 10000000 |
9 | |
10 | #include <string.h> |
11 | #include <stdio.h> |
12 | #include <stdlib.h> |
13 | #include <unistd.h> |
14 | #include <time.h> |
15 | #include <sys/types.h> |
16 | #include <sys/time.h> |
17 | #include <sys/syscall.h> |
18 | #include <signal.h> |
19 | |
20 | static volatile int soak_done; |
21 | unsigned long long clock_frequency; |
22 | unsigned long long timebase_frequency; |
23 | double timebase_multiplier; |
24 | |
25 | static inline unsigned long mftb(void) |
26 | { |
27 | unsigned long low; |
28 | |
29 | asm volatile("mftb %0" : "=r" (low)); |
30 | |
31 | return low; |
32 | } |
33 | |
34 | static void sigalrm_handler(int unused) |
35 | { |
36 | soak_done = 1; |
37 | } |
38 | |
39 | /* |
40 | * Use a timer instead of busy looping on clock_gettime() so we don't |
41 | * pollute profiles with glibc and VDSO hits. |
42 | */ |
43 | static void cpu_soak_usecs(unsigned long usecs) |
44 | { |
45 | struct itimerval val; |
46 | |
47 | memset(&val, 0, sizeof(val)); |
48 | val.it_value.tv_usec = usecs; |
49 | |
50 | signal(SIGALRM, sigalrm_handler); |
51 | setitimer(ITIMER_REAL, &val, NULL); |
52 | |
53 | while (1) { |
54 | if (soak_done) |
55 | break; |
56 | } |
57 | |
58 | signal(SIGALRM, SIG_DFL); |
59 | } |
60 | |
61 | /* |
62 | * This only works with recent kernels where cpufreq modifies |
63 | * /proc/cpuinfo dynamically. |
64 | */ |
65 | static void get_proc_frequency(void) |
66 | { |
67 | FILE *f; |
68 | char line[128]; |
69 | char *p, *end; |
70 | unsigned long v; |
71 | double d; |
72 | char *override; |
73 | |
74 | /* Try to get out of low power/low frequency mode */ |
75 | cpu_soak_usecs(usecs: 0.25 * 1000000); |
76 | |
77 | f = fopen("/proc/cpuinfo" , "r" ); |
78 | if (f == NULL) |
79 | return; |
80 | |
81 | timebase_frequency = 0; |
82 | |
83 | while (fgets(line, sizeof(line), f) != NULL) { |
84 | if (strncmp(line, "timebase" , 8) == 0) { |
85 | p = strchr(line, ':'); |
86 | if (p != NULL) { |
87 | v = strtoull(p + 1, &end, 0); |
88 | if (end != p + 1) |
89 | timebase_frequency = v; |
90 | } |
91 | } |
92 | |
93 | if (((strncmp(line, "clock" , 5) == 0) || |
94 | (strncmp(line, "cpu MHz" , 7) == 0))) { |
95 | p = strchr(line, ':'); |
96 | if (p != NULL) { |
97 | d = strtod(p + 1, &end); |
98 | if (end != p + 1) { |
99 | /* Find fastest clock frequency */ |
100 | if ((d * 1000000ULL) > clock_frequency) |
101 | clock_frequency = d * 1000000ULL; |
102 | } |
103 | } |
104 | } |
105 | } |
106 | |
107 | fclose(f); |
108 | |
109 | override = getenv("FREQUENCY" ); |
110 | if (override) |
111 | clock_frequency = strtoull(override, NULL, 10); |
112 | |
113 | if (timebase_frequency) |
114 | timebase_multiplier = (double)clock_frequency |
115 | / timebase_frequency; |
116 | else |
117 | timebase_multiplier = 1; |
118 | } |
119 | |
120 | static void do_null_syscall(unsigned long nr) |
121 | { |
122 | unsigned long i; |
123 | |
124 | for (i = 0; i < nr; i++) |
125 | syscall(__NR_gettid); |
126 | } |
127 | |
128 | #define TIME(A, STR) \ |
129 | |
130 | int main(void) |
131 | { |
132 | unsigned long tb_start, tb_now; |
133 | struct timespec tv_start, tv_now; |
134 | unsigned long long elapsed_ns, elapsed_tb; |
135 | |
136 | get_proc_frequency(); |
137 | |
138 | clock_gettime(CLOCK_MONOTONIC, &tv_start); |
139 | tb_start = mftb(); |
140 | |
141 | do_null_syscall(NR_LOOPS); |
142 | |
143 | clock_gettime(CLOCK_MONOTONIC, &tv_now); |
144 | tb_now = mftb(); |
145 | |
146 | elapsed_ns = (tv_now.tv_sec - tv_start.tv_sec) * 1000000000ULL + |
147 | (tv_now.tv_nsec - tv_start.tv_nsec); |
148 | elapsed_tb = tb_now - tb_start; |
149 | |
150 | printf("%10.2f ns %10.2f cycles\n" , (float)elapsed_ns / NR_LOOPS, |
151 | (float)elapsed_tb * timebase_multiplier / NR_LOOPS); |
152 | |
153 | return 0; |
154 | } |
155 | |