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authorGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
committerGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
commitc2e754829628d1e9b7a16b3389cfdace76950fdf (patch)
tree5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/base/internal/sysinfo.cc
Initial Commit
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+// 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"
+
+#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
+
+#ifdef __APPLE__
+#include <sys/sysctl.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"
+#include "absl/base/thread_annotations.h"
+
+namespace absl {
+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__) || defined(__GENCLAVE__)
+ // TODO(b/28296132): Calling std::thread::hardware_concurrency() induces a
+ // link error on myriad2 builds.
+ // TODO(b/62709537): Support std::thread::hardware_concurrency() in gEnclalve.
+ 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);
+}
+
+#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
+} // namespace absl