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ebabbf58 | 1 | /* |
c0c0989a | 2 | * SPDX-License-Identifier: LGPL-2.1-only |
ebabbf58 MD |
3 | * |
4 | * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
5 | * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com> | |
ebabbf58 MD |
6 | */ |
7 | ||
ebabbf58 | 8 | #define _LGPL_SOURCE |
66dbdc34 MJ |
9 | #include <assert.h> |
10 | #include <ctype.h> | |
11 | #include <errno.h> | |
12 | #include <fcntl.h> | |
ebabbf58 MD |
13 | #include <unistd.h> |
14 | #include <pthread.h> | |
66dbdc34 | 15 | #include <stdlib.h> |
ebabbf58 | 16 | |
74cc1f59 MJ |
17 | #include <urcu/compiler.h> |
18 | ||
66dbdc34 MJ |
19 | #include "common/align.h" |
20 | #include "common/logging.h" | |
74cc1f59 MJ |
21 | #include "common/smp.h" |
22 | ||
23 | static int num_possible_cpus_cache; | |
ebabbf58 MD |
24 | |
25 | #if (defined(__GLIBC__) || defined( __UCLIBC__)) | |
66dbdc34 | 26 | int get_num_possible_cpus_fallback(void) |
ebabbf58 | 27 | { |
ebabbf58 MD |
28 | /* On Linux, when some processors are offline |
29 | * _SC_NPROCESSORS_CONF counts the offline | |
30 | * processors, whereas _SC_NPROCESSORS_ONLN | |
31 | * does not. If we used _SC_NPROCESSORS_ONLN, | |
32 | * getcpu() could return a value greater than | |
33 | * this sysconf, in which case the arrays | |
34 | * indexed by processor would overflow. | |
35 | */ | |
66dbdc34 | 36 | return sysconf(_SC_NPROCESSORS_CONF); |
ebabbf58 MD |
37 | } |
38 | ||
39 | #else | |
40 | ||
41 | /* | |
42 | * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not | |
43 | * return the number of configured CPUs in the system but relies on the cpu | |
44 | * affinity mask of the current task. | |
45 | * | |
46 | * So instead we use a strategy similar to GLIBC's, counting the cpu | |
47 | * directories in "/sys/devices/system/cpu" and fallback on the value from | |
48 | * sysconf if it fails. | |
49 | */ | |
50 | ||
51 | #include <dirent.h> | |
52 | #include <limits.h> | |
53 | #include <stdlib.h> | |
54 | #include <string.h> | |
55 | #include <sys/types.h> | |
56 | ||
57 | #define __max(a,b) ((a)>(b)?(a):(b)) | |
58 | ||
66dbdc34 | 59 | int get_num_possible_cpus_fallback(void) |
ebabbf58 | 60 | { |
66dbdc34 | 61 | int count = 0; |
ebabbf58 MD |
62 | DIR *cpudir; |
63 | struct dirent *entry; | |
64 | ||
65 | cpudir = opendir("/sys/devices/system/cpu"); | |
66 | if (cpudir == NULL) | |
67 | goto end; | |
68 | ||
69 | /* | |
70 | * Count the number of directories named "cpu" followed by and | |
71 | * integer. This is the same strategy as glibc uses. | |
72 | */ | |
73 | while ((entry = readdir(cpudir))) { | |
74 | if (entry->d_type == DT_DIR && | |
75 | strncmp(entry->d_name, "cpu", 3) == 0) { | |
76 | ||
77 | char *endptr; | |
78 | unsigned long cpu_num; | |
79 | ||
80 | cpu_num = strtoul(entry->d_name + 3, &endptr, 10); | |
81 | if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3) | |
82 | && (*endptr == '\0')) { | |
83 | count++; | |
84 | } | |
85 | } | |
86 | } | |
87 | ||
88 | end: | |
89 | /* | |
90 | * Get the sysconf value as a fallback. Keep the highest number. | |
91 | */ | |
66dbdc34 MJ |
92 | return __max(sysconf(_SC_NPROCESSORS_CONF), count); |
93 | } | |
94 | #endif | |
95 | ||
96 | /* | |
97 | * Get the CPU possible mask string from sysfs. | |
98 | * | |
99 | * buf: the buffer where the mask will be read. | |
100 | * max_bytes: the maximum number of bytes to write in the buffer. | |
101 | * | |
102 | * Returns the number of bytes read or -1 on error. | |
103 | */ | |
104 | int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes) | |
105 | { | |
106 | ssize_t bytes_read = 0; | |
107 | size_t total_bytes_read = 0; | |
108 | int fd = 0; | |
109 | ||
110 | if (buf == NULL) | |
111 | return -1; | |
112 | ||
113 | fd = open("/sys/devices/system/cpu/possible", O_RDONLY); | |
114 | if (fd < 0) | |
115 | return -1; | |
116 | ||
117 | do { | |
118 | bytes_read = read(fd, buf + total_bytes_read, | |
119 | max_bytes - total_bytes_read); | |
120 | ||
121 | if (bytes_read < 0) { | |
122 | if (errno == EINTR) { | |
123 | continue; /* retry operation */ | |
124 | } else { | |
125 | return -1; | |
126 | } | |
127 | } | |
128 | ||
129 | total_bytes_read += bytes_read; | |
130 | assert(total_bytes_read <= max_bytes); | |
131 | } while (max_bytes > total_bytes_read && bytes_read > 0); | |
132 | ||
133 | if (close(fd)) | |
134 | PERROR("close"); | |
135 | ||
136 | /* | |
137 | * Make sure the mask read is a null terminated string. | |
138 | */ | |
139 | if (total_bytes_read < max_bytes) | |
140 | buf[total_bytes_read] = '\0'; | |
141 | else | |
142 | buf[max_bytes - 1] = '\0'; | |
143 | ||
144 | return total_bytes_read; | |
145 | } | |
146 | ||
147 | /* | |
148 | * Get the number of CPUs from the possible cpu mask. | |
149 | * | |
150 | * pmask: the mask to parse. | |
151 | * len: the len of the mask excluding '\0'. | |
152 | * | |
153 | * Returns the number of possible CPUs from the mask or 0 on error. | |
154 | */ | |
155 | int get_num_possible_cpus_from_mask(const char *pmask, size_t len) | |
156 | { | |
157 | ssize_t i; | |
158 | unsigned long cpu_index; | |
159 | char *endptr; | |
160 | ||
161 | /* We need at least one char to read */ | |
162 | if (len < 1) | |
163 | goto error; | |
164 | ||
165 | /* Start from the end to read the last CPU index. */ | |
166 | for (i = len - 1; i > 0; i--) { | |
167 | /* Break when we hit the first separator. */ | |
168 | if ((pmask[i] == ',') || (pmask[i] == '-')) { | |
169 | i++; | |
170 | break; | |
171 | } | |
172 | } | |
173 | ||
174 | cpu_index = strtoul(&pmask[i], &endptr, 10); | |
ebabbf58 MD |
175 | |
176 | /* | |
66dbdc34 MJ |
177 | * If we read a CPU index, increment it by one to return a number of |
178 | * CPUs. | |
ebabbf58 | 179 | */ |
66dbdc34 MJ |
180 | if ((&pmask[i] != endptr) && (cpu_index < INT_MAX)) |
181 | return (int) cpu_index + 1; | |
182 | ||
183 | error: | |
184 | return 0; | |
185 | } | |
186 | ||
187 | static void _get_num_possible_cpus(void) | |
188 | { | |
189 | int ret; | |
190 | int buf_len = LTTNG_UST_PAGE_SIZE; | |
191 | char buf[buf_len]; | |
192 | ||
193 | /* Get the possible cpu mask from sysfs, fallback to sysconf. */ | |
194 | ret = get_possible_cpu_mask_from_sysfs((char *) &buf, buf_len); | |
195 | if (ret <= 0) | |
196 | goto fallback; | |
197 | ||
198 | /* Parse the possible cpu mask, on failure fallback to sysconf. */ | |
199 | ret = get_num_possible_cpus_from_mask((char *) &buf, ret); | |
200 | if (ret > 0) | |
201 | goto end; | |
202 | ||
203 | fallback: | |
204 | /* Fallback to sysconf. */ | |
205 | ret = get_num_possible_cpus_fallback(); | |
206 | ||
207 | end: | |
208 | /* If all methods failed, don't store the value. */ | |
209 | if (ret < 1) | |
ebabbf58 | 210 | return; |
66dbdc34 MJ |
211 | |
212 | num_possible_cpus_cache = ret; | |
ebabbf58 | 213 | } |
74cc1f59 MJ |
214 | |
215 | /* | |
216 | * Returns the total number of CPUs in the system. If the cache is not yet | |
66dbdc34 MJ |
217 | * initialized, get the value from "/sys/devices/system/cpu/possible" or |
218 | * fallback to sysconf and cache it. | |
74cc1f59 | 219 | * |
66dbdc34 | 220 | * If all methods fail, don't populate the cache and return 0. |
74cc1f59 MJ |
221 | */ |
222 | int num_possible_cpus(void) | |
223 | { | |
224 | if (caa_unlikely(!num_possible_cpus_cache)) | |
225 | _get_num_possible_cpus(); | |
226 | ||
227 | return num_possible_cpus_cache; | |
228 | } |