// 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 // // https://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. // // UnscaledCycleClock // An UnscaledCycleClock yields the value and frequency of a cycle counter // that increments at a rate that is approximately constant. // This class is for internal use only, you should consider using CycleClock // instead. // // Notes: // The cycle counter frequency is not necessarily the core clock frequency. // That is, CycleCounter cycles are not necessarily "CPU cycles". // // An arbitrary offset may have been added to the counter at power on. // // On some platforms, the rate and offset of the counter may differ // slightly when read from different CPUs of a multiprocessor. Usually, // we try to ensure that the operating system adjusts values periodically // so that values agree approximately. If you need stronger guarantees, // consider using alternate interfaces. // // The CPU is not required to maintain the ordering of a cycle counter read // with respect to surrounding instructions. #ifndef ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_ #define ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_ #include #if defined(__APPLE__) #include #endif #include "absl/base/port.h" // The following platforms have an implementation of a hardware counter. #if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \ defined(__powerpc__) || defined(__ppc__) || defined(__riscv) || \ defined(_M_IX86) || (defined(_M_X64) && !defined(_M_ARM64EC)) #define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 1 #else #define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 0 #endif // The following platforms often disable access to the hardware // counter (through a sandbox) even if the underlying hardware has a // usable counter. The CycleTimer interface also requires a *scaled* // CycleClock that runs at atleast 1 MHz. We've found some Android // ARM64 devices where this is not the case, so we disable it by // default on Android ARM64. #if defined(__native_client__) || \ (defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE) || \ (defined(__ANDROID__) && defined(__aarch64__)) #define ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT 0 #else #define ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT 1 #endif // UnscaledCycleClock is an optional internal feature. // Use "#if ABSL_USE_UNSCALED_CYCLECLOCK" to test for its presence. // Can be overridden at compile-time via -DABSL_USE_UNSCALED_CYCLECLOCK=0|1 #if !defined(ABSL_USE_UNSCALED_CYCLECLOCK) #define ABSL_USE_UNSCALED_CYCLECLOCK \ (ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION && \ ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT) #endif #if ABSL_USE_UNSCALED_CYCLECLOCK // This macro can be used to test if UnscaledCycleClock::Frequency() // is NominalCPUFrequency() on a particular platform. #if (defined(__i386__) || defined(__x86_64__) || defined(__riscv) || \ defined(_M_IX86) || defined(_M_X64)) #define ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY #endif namespace absl { ABSL_NAMESPACE_BEGIN namespace time_internal { class UnscaledCycleClockWrapperForGetCurrentTime; } // namespace time_internal namespace base_internal { class CycleClock; class UnscaledCycleClockWrapperForInitializeFrequency; class UnscaledCycleClock { private: UnscaledCycleClock() = delete; // Return the value of a cycle counter that counts at a rate that is // approximately constant. static int64_t Now(); // Return the how much UnscaledCycleClock::Now() increases per second. // This is not necessarily the core CPU clock frequency. // It may be the nominal value report by the kernel, rather than a measured // value. static double Frequency(); // Allowed users friend class base_internal::CycleClock; friend class time_internal::UnscaledCycleClockWrapperForGetCurrentTime; friend class base_internal::UnscaledCycleClockWrapperForInitializeFrequency; }; #if defined(__x86_64__) inline int64_t UnscaledCycleClock::Now() { uint64_t low, high; __asm__ volatile("rdtsc" : "=a"(low), "=d"(high)); return (high << 32) | low; } #endif } // namespace base_internal ABSL_NAMESPACE_END } // namespace absl #endif // ABSL_USE_UNSCALED_CYCLECLOCK #endif // ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_