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53 lines
1.3 KiB
C++
53 lines
1.3 KiB
C++
#ifndef RDTSC_H
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#define RDTSC_H
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#include <stdint.h> // uint64_t
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#if defined(_M_X64) || defined(_M_IX86) || defined(__x86_64) || defined(__i386)
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# ifdef _WIN32
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# include <intrin.h> // __rdtsc
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# else
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# include <x86intrin.h> // __rdtsc
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# endif
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# define HAS_HW_RDTSC 1
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#else
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# include <chrono> // std::chrono::high_resolution_clock
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# define HAS_HW_RDTSC 0
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#endif
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inline uint64_t rdtsc()
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{
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#if HAS_HW_RDTSC
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// _mm_lfence() might be used to serialize the instruction stream,
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// and it would guarantee that RDTSC will not be reordered with
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// other instructions. However, measurements show that the overhead
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// may be too big (easily 15 to 30 CPU cycles) for profiling
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// purposes: if reordering matters, the overhead matters too!
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// Forbid the compiler from reordering instructions
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# ifdef _MSC_VER
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_ReadWriteBarrier();
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# else
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__asm__ __volatile__("" : : : "memory");
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# endif
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uint64_t result = __rdtsc();
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// Forbid the compiler from reordering instructions
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# ifdef _MSC_VER
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_ReadWriteBarrier();
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# else
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__asm__ __volatile__("" : : : "memory");
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# endif
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return result;
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#else
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auto now = std::chrono::high_resolution_clock::now();
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return std::chrono::duration_cast<std::chrono::nanoseconds>(
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now.time_since_epoch())
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.count();
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#endif
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}
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#endif // RDTSC_H
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