172 lines
7.1 KiB
C++
172 lines
7.1 KiB
C++
// ----------------------------------------------------------------------
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// CycleClock
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// A CycleClock tells you the current time in Cycles. The "time"
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// is actually time since power-on. This is like time() but doesn't
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// involve a system call and is much more precise.
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//
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// NOTE: Not all cpu/platform/kernel combinations guarantee that this
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// clock increments at a constant rate or is synchronized across all logical
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// cpus in a system.
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//
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// If you need the above guarantees, please consider using a different
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// API. There are efforts to provide an interface which provides a millisecond
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// granularity and implemented as a memory read. A memory read is generally
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// cheaper than the CycleClock for many architectures.
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//
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// Also, in some out of order CPU implementations, the CycleClock is not
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// serializing. So if you're trying to count at cycles granularity, your
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// data might be inaccurate due to out of order instruction execution.
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// ----------------------------------------------------------------------
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#ifndef BENCHMARK_CYCLECLOCK_H_
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#define BENCHMARK_CYCLECLOCK_H_
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#include <cstdint>
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#include "benchmark/benchmark.h"
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#include "internal_macros.h"
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#if defined(BENCHMARK_OS_MACOSX)
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#include <mach/mach_time.h>
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#endif
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// For MSVC, we want to use '_asm rdtsc' when possible (since it works
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// with even ancient MSVC compilers), and when not possible the
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// __rdtsc intrinsic, declared in <intrin.h>. Unfortunately, in some
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// environments, <windows.h> and <intrin.h> have conflicting
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// declarations of some other intrinsics, breaking compilation.
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// Therefore, we simply declare __rdtsc ourselves. See also
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// http://connect.microsoft.com/VisualStudio/feedback/details/262047
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#if defined(COMPILER_MSVC) && !defined(_M_IX86)
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extern "C" uint64_t __rdtsc();
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#pragma intrinsic(__rdtsc)
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#endif
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#ifndef BENCHMARK_OS_WINDOWS
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#include <sys/time.h>
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#include <time.h>
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#endif
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#ifdef BENCHMARK_OS_EMSCRIPTEN
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#include <emscripten.h>
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#endif
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namespace benchmark {
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// NOTE: only i386 and x86_64 have been well tested.
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// PPC, sparc, alpha, and ia64 are based on
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// http://peter.kuscsik.com/wordpress/?p=14
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// with modifications by m3b. See also
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// https://setisvn.ssl.berkeley.edu/svn/lib/fftw-3.0.1/kernel/cycle.h
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namespace cycleclock {
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// This should return the number of cycles since power-on. Thread-safe.
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inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
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#if defined(BENCHMARK_OS_MACOSX)
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// this goes at the top because we need ALL Macs, regardless of
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// architecture, to return the number of "mach time units" that
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// have passed since startup. See sysinfo.cc where
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// InitializeSystemInfo() sets the supposed cpu clock frequency of
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// macs to the number of mach time units per second, not actual
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// CPU clock frequency (which can change in the face of CPU
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// frequency scaling). Also note that when the Mac sleeps, this
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// counter pauses; it does not continue counting, nor does it
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// reset to zero.
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return mach_absolute_time();
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#elif defined(BENCHMARK_OS_EMSCRIPTEN)
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// this goes above x86-specific code because old versions of Emscripten
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// define __x86_64__, although they have nothing to do with it.
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return static_cast<int64_t>(emscripten_get_now() * 1e+6);
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#elif defined(__i386__)
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int64_t ret;
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__asm__ volatile("rdtsc" : "=A"(ret));
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return ret;
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#elif defined(__x86_64__) || defined(__amd64__)
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uint64_t low, high;
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__asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
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return (high << 32) | low;
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#elif defined(__powerpc__) || defined(__ppc__)
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// This returns a time-base, which is not always precisely a cycle-count.
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int64_t tbl, tbu0, tbu1;
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asm("mftbu %0" : "=r"(tbu0));
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asm("mftb %0" : "=r"(tbl));
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asm("mftbu %0" : "=r"(tbu1));
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tbl &= -static_cast<int64_t>(tbu0 == tbu1);
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// high 32 bits in tbu1; low 32 bits in tbl (tbu0 is garbage)
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return (tbu1 << 32) | tbl;
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#elif defined(__sparc__)
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int64_t tick;
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asm(".byte 0x83, 0x41, 0x00, 0x00");
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asm("mov %%g1, %0" : "=r"(tick));
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return tick;
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#elif defined(__ia64__)
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int64_t itc;
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asm("mov %0 = ar.itc" : "=r"(itc));
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return itc;
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#elif defined(COMPILER_MSVC) && defined(_M_IX86)
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// Older MSVC compilers (like 7.x) don't seem to support the
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// __rdtsc intrinsic properly, so I prefer to use _asm instead
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// when I know it will work. Otherwise, I'll use __rdtsc and hope
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// the code is being compiled with a non-ancient compiler.
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_asm rdtsc
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#elif defined(COMPILER_MSVC)
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return __rdtsc();
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#elif defined(BENCHMARK_OS_NACL)
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// Native Client validator on x86/x86-64 allows RDTSC instructions,
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// and this case is handled above. Native Client validator on ARM
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// rejects MRC instructions (used in the ARM-specific sequence below),
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// so we handle it here. Portable Native Client compiles to
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// architecture-agnostic bytecode, which doesn't provide any
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// cycle counter access mnemonics.
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// Native Client does not provide any API to access cycle counter.
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// Use clock_gettime(CLOCK_MONOTONIC, ...) instead of gettimeofday
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// because is provides nanosecond resolution (which is noticable at
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// least for PNaCl modules running on x86 Mac & Linux).
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// Initialize to always return 0 if clock_gettime fails.
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struct timespec ts = { 0, 0 };
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clock_gettime(CLOCK_MONOTONIC, &ts);
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return static_cast<int64_t>(ts.tv_sec) * 1000000000 + ts.tv_nsec;
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#elif defined(__aarch64__)
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// System timer of ARMv8 runs at a different frequency than the CPU's.
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// The frequency is fixed, typically in the range 1-50MHz. It can be
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// read at CNTFRQ special register. We assume the OS has set up
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// the virtual timer properly.
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int64_t virtual_timer_value;
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asm volatile("mrs %0, cntvct_el0" : "=r"(virtual_timer_value));
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return virtual_timer_value;
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#elif defined(__ARM_ARCH)
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// V6 is the earliest arch that has a standard cyclecount
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// Native Client validator doesn't allow MRC instructions.
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#if (__ARM_ARCH >= 6)
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uint32_t pmccntr;
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uint32_t pmuseren;
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uint32_t pmcntenset;
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// Read the user mode perf monitor counter access permissions.
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asm volatile("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
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if (pmuseren & 1) { // Allows reading perfmon counters for user mode code.
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asm volatile("mrc p15, 0, %0, c9, c12, 1" : "=r"(pmcntenset));
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if (pmcntenset & 0x80000000ul) { // Is it counting?
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asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(pmccntr));
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// The counter is set up to count every 64th cycle
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return static_cast<int64_t>(pmccntr) * 64; // Should optimize to << 6
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}
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}
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#endif
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struct timeval tv;
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gettimeofday(&tv, nullptr);
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return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
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#elif defined(__mips__)
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// mips apparently only allows rdtsc for superusers, so we fall
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// back to gettimeofday. It's possible clock_gettime would be better.
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struct timeval tv;
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gettimeofday(&tv, nullptr);
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return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
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#else
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// The soft failover to a generic implementation is automatic only for ARM.
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// For other platforms the developer is expected to make an attempt to create
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// a fast implementation and use generic version if nothing better is available.
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#error You need to define CycleTimer for your OS and CPU
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#endif
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}
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} // end namespace cycleclock
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} // end namespace benchmark
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#endif // BENCHMARK_CYCLECLOCK_H_
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