summaryrefslogtreecommitdiff
path: root/absl/base/internal/sysinfo.cc
blob: ce14fc0f61edba3c0408c7750e692085362d8631 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "absl/base/internal/sysinfo.h"

#include "absl/base/attributes.h"

#ifdef _WIN32
#include <shlwapi.h>
#include <windows.h>
#else
#include <fcntl.h>
#include <pthread.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#endif

#ifdef __linux__
#include <sys/syscall.h>
#endif

#if defined(__APPLE__) || defined(__FreeBSD__)
#include <sys/sysctl.h>
#endif

#if defined(__myriad2__)
#include <rtems.h>
#endif

#include <string.h>
#include <cassert>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <limits>
#include <thread>  // NOLINT(build/c++11)
#include <utility>
#include <vector>

#include "absl/base/call_once.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/internal/unscaledcycleclock.h"

namespace absl {
inline namespace lts_2018_12_18 {
namespace base_internal {

static once_flag init_system_info_once;
static int num_cpus = 0;
static double nominal_cpu_frequency = 1.0;  // 0.0 might be dangerous.

static int GetNumCPUs() {
#if defined(__myriad2__)
  return 1;
#else
  // Other possibilities:
  //  - Read /sys/devices/system/cpu/online and use cpumask_parse()
  //  - sysconf(_SC_NPROCESSORS_ONLN)
  return std::thread::hardware_concurrency();
#endif
}

#if defined(_WIN32)

static double GetNominalCPUFrequency() {
  DWORD data;
  DWORD data_size = sizeof(data);
  #pragma comment(lib, "shlwapi.lib")  // For SHGetValue().
  if (SUCCEEDED(
          SHGetValueA(HKEY_LOCAL_MACHINE,
                      "HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0",
                      "~MHz", nullptr, &data, &data_size))) {
    return data * 1e6;  // Value is MHz.
  }
  return 1.0;
}

#elif defined(CTL_HW) && defined(HW_CPU_FREQ)

static double GetNominalCPUFrequency() {
  unsigned freq;
  size_t size = sizeof(freq);
  int mib[2] = {CTL_HW, HW_CPU_FREQ};
  if (sysctl(mib, 2, &freq, &size, nullptr, 0) == 0) {
    return static_cast<double>(freq);
  }
  return 1.0;
}

#else

// Helper function for reading a long from a file. Returns true if successful
// and the memory location pointed to by value is set to the value read.
static bool ReadLongFromFile(const char *file, long *value) {
  bool ret = false;
  int fd = open(file, O_RDONLY);
  if (fd != -1) {
    char line[1024];
    char *err;
    memset(line, '\0', sizeof(line));
    int len = read(fd, line, sizeof(line) - 1);
    if (len <= 0) {
      ret = false;
    } else {
      const long temp_value = strtol(line, &err, 10);
      if (line[0] != '\0' && (*err == '\n' || *err == '\0')) {
        *value = temp_value;
        ret = true;
      }
    }
    close(fd);
  }
  return ret;
}

#if defined(ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY)

// Reads a monotonic time source and returns a value in
// nanoseconds. The returned value uses an arbitrary epoch, not the
// Unix epoch.
static int64_t ReadMonotonicClockNanos() {
  struct timespec t;
#ifdef CLOCK_MONOTONIC_RAW
  int rc = clock_gettime(CLOCK_MONOTONIC_RAW, &t);
#else
  int rc = clock_gettime(CLOCK_MONOTONIC, &t);
#endif
  if (rc != 0) {
    perror("clock_gettime() failed");
    abort();
  }
  return int64_t{t.tv_sec} * 1000000000 + t.tv_nsec;
}

class UnscaledCycleClockWrapperForInitializeFrequency {
 public:
  static int64_t Now() { return base_internal::UnscaledCycleClock::Now(); }
};

struct TimeTscPair {
  int64_t time;  // From ReadMonotonicClockNanos().
  int64_t tsc;   // From UnscaledCycleClock::Now().
};

// Returns a pair of values (monotonic kernel time, TSC ticks) that
// approximately correspond to each other.  This is accomplished by
// doing several reads and picking the reading with the lowest
// latency.  This approach is used to minimize the probability that
// our thread was preempted between clock reads.
static TimeTscPair GetTimeTscPair() {
  int64_t best_latency = std::numeric_limits<int64_t>::max();
  TimeTscPair best;
  for (int i = 0; i < 10; ++i) {
    int64_t t0 = ReadMonotonicClockNanos();
    int64_t tsc = UnscaledCycleClockWrapperForInitializeFrequency::Now();
    int64_t t1 = ReadMonotonicClockNanos();
    int64_t latency = t1 - t0;
    if (latency < best_latency) {
      best_latency = latency;
      best.time = t0;
      best.tsc = tsc;
    }
  }
  return best;
}

// Measures and returns the TSC frequency by taking a pair of
// measurements approximately `sleep_nanoseconds` apart.
static double MeasureTscFrequencyWithSleep(int sleep_nanoseconds) {
  auto t0 = GetTimeTscPair();
  struct timespec ts;
  ts.tv_sec = 0;
  ts.tv_nsec = sleep_nanoseconds;
  while (nanosleep(&ts, &ts) != 0 && errno == EINTR) {}
  auto t1 = GetTimeTscPair();
  double elapsed_ticks = t1.tsc - t0.tsc;
  double elapsed_time = (t1.time - t0.time) * 1e-9;
  return elapsed_ticks / elapsed_time;
}

// Measures and returns the TSC frequency by calling
// MeasureTscFrequencyWithSleep(), doubling the sleep interval until the
// frequency measurement stabilizes.
static double MeasureTscFrequency() {
  double last_measurement = -1.0;
  int sleep_nanoseconds = 1000000;  // 1 millisecond.
  for (int i = 0; i < 8; ++i) {
    double measurement = MeasureTscFrequencyWithSleep(sleep_nanoseconds);
    if (measurement * 0.99 < last_measurement &&
        last_measurement < measurement * 1.01) {
      // Use the current measurement if it is within 1% of the
      // previous measurement.
      return measurement;
    }
    last_measurement = measurement;
    sleep_nanoseconds *= 2;
  }
  return last_measurement;
}

#endif  // ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY

static double GetNominalCPUFrequency() {
  long freq = 0;

  // Google's production kernel has a patch to export the TSC
  // frequency through sysfs. If the kernel is exporting the TSC
  // frequency use that. There are issues where cpuinfo_max_freq
  // cannot be relied on because the BIOS may be exporting an invalid
  // p-state (on x86) or p-states may be used to put the processor in
  // a new mode (turbo mode). Essentially, those frequencies cannot
  // always be relied upon. The same reasons apply to /proc/cpuinfo as
  // well.
  if (ReadLongFromFile("/sys/devices/system/cpu/cpu0/tsc_freq_khz", &freq)) {
    return freq * 1e3;  // Value is kHz.
  }

#if defined(ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY)
  // On these platforms, the TSC frequency is the nominal CPU
  // frequency.  But without having the kernel export it directly
  // though /sys/devices/system/cpu/cpu0/tsc_freq_khz, there is no
  // other way to reliably get the TSC frequency, so we have to
  // measure it ourselves.  Some CPUs abuse cpuinfo_max_freq by
  // exporting "fake" frequencies for implementing new features. For
  // example, Intel's turbo mode is enabled by exposing a p-state
  // value with a higher frequency than that of the real TSC
  // rate. Because of this, we prefer to measure the TSC rate
  // ourselves on i386 and x86-64.
  return MeasureTscFrequency();
#else

  // If CPU scaling is in effect, we want to use the *maximum*
  // frequency, not whatever CPU speed some random processor happens
  // to be using now.
  if (ReadLongFromFile("/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq",
                       &freq)) {
    return freq * 1e3;  // Value is kHz.
  }

  return 1.0;
#endif  // !ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
}

#endif

// InitializeSystemInfo() may be called before main() and before
// malloc is properly initialized, therefore this must not allocate
// memory.
static void InitializeSystemInfo() {
  num_cpus = GetNumCPUs();
  nominal_cpu_frequency = GetNominalCPUFrequency();
}

int NumCPUs() {
  base_internal::LowLevelCallOnce(&init_system_info_once, InitializeSystemInfo);
  return num_cpus;
}

double NominalCPUFrequency() {
  base_internal::LowLevelCallOnce(&init_system_info_once, InitializeSystemInfo);
  return nominal_cpu_frequency;
}

#if defined(_WIN32)

pid_t GetTID() {
  return GetCurrentThreadId();
}

#elif defined(__linux__)

#ifndef SYS_gettid
#define SYS_gettid __NR_gettid
#endif

pid_t GetTID() {
  return syscall(SYS_gettid);
}

#elif defined(__akaros__)

pid_t GetTID() {
  // Akaros has a concept of "vcore context", which is the state the program
  // is forced into when we need to make a user-level scheduling decision, or
  // run a signal handler.  This is analogous to the interrupt context that a
  // CPU might enter if it encounters some kind of exception.
  //
  // There is no current thread context in vcore context, but we need to give
  // a reasonable answer if asked for a thread ID (e.g., in a signal handler).
  // Thread 0 always exists, so if we are in vcore context, we return that.
  //
  // Otherwise, we know (since we are using pthreads) that the uthread struct
  // current_uthread is pointing to is the first element of a
  // struct pthread_tcb, so we extract and return the thread ID from that.
  //
  // TODO(dcross): Akaros anticipates moving the thread ID to the uthread
  // structure at some point. We should modify this code to remove the cast
  // when that happens.
  if (in_vcore_context())
    return 0;
  return reinterpret_cast<struct pthread_tcb *>(current_uthread)->id;
}

#elif defined(__myriad2__)

pid_t GetTID() {
  uint32_t tid;
  rtems_task_ident(RTEMS_SELF, 0, &tid);
  return tid;
}

#else

// Fallback implementation of GetTID using pthread_getspecific.
static once_flag tid_once;
static pthread_key_t tid_key;
static absl::base_internal::SpinLock tid_lock(
    absl::base_internal::kLinkerInitialized);

// We set a bit per thread in this array to indicate that an ID is in
// use. ID 0 is unused because it is the default value returned by
// pthread_getspecific().
static std::vector<uint32_t>* tid_array GUARDED_BY(tid_lock) = nullptr;
static constexpr int kBitsPerWord = 32;  // tid_array is uint32_t.

// Returns the TID to tid_array.
static void FreeTID(void *v) {
  intptr_t tid = reinterpret_cast<intptr_t>(v);
  int word = tid / kBitsPerWord;
  uint32_t mask = ~(1u << (tid % kBitsPerWord));
  absl::base_internal::SpinLockHolder lock(&tid_lock);
  assert(0 <= word && static_cast<size_t>(word) < tid_array->size());
  (*tid_array)[word] &= mask;
}

static void InitGetTID() {
  if (pthread_key_create(&tid_key, FreeTID) != 0) {
    // The logging system calls GetTID() so it can't be used here.
    perror("pthread_key_create failed");
    abort();
  }

  // Initialize tid_array.
  absl::base_internal::SpinLockHolder lock(&tid_lock);
  tid_array = new std::vector<uint32_t>(1);
  (*tid_array)[0] = 1;  // ID 0 is never-allocated.
}

// Return a per-thread small integer ID from pthread's thread-specific data.
pid_t GetTID() {
  absl::call_once(tid_once, InitGetTID);

  intptr_t tid = reinterpret_cast<intptr_t>(pthread_getspecific(tid_key));
  if (tid != 0) {
    return tid;
  }

  int bit;  // tid_array[word] = 1u << bit;
  size_t word;
  {
    // Search for the first unused ID.
    absl::base_internal::SpinLockHolder lock(&tid_lock);
    // First search for a word in the array that is not all ones.
    word = 0;
    while (word < tid_array->size() && ~(*tid_array)[word] == 0) {
      ++word;
    }
    if (word == tid_array->size()) {
      tid_array->push_back(0);  // No space left, add kBitsPerWord more IDs.
    }
    // Search for a zero bit in the word.
    bit = 0;
    while (bit < kBitsPerWord && (((*tid_array)[word] >> bit) & 1) != 0) {
      ++bit;
    }
    tid = (word * kBitsPerWord) + bit;
    (*tid_array)[word] |= 1u << bit;  // Mark the TID as allocated.
  }

  if (pthread_setspecific(tid_key, reinterpret_cast<void *>(tid)) != 0) {
    perror("pthread_setspecific failed");
    abort();
  }

  return static_cast<pid_t>(tid);
}

#endif

}  // namespace base_internal
}  // inline namespace lts_2018_12_18
}  // namespace absl