blob: b87a8798c3c13e87b6fb859633787e1337dcfd09 [file] [log] [blame]
// ----------------------------------------------------------------------
// CycleClock
// A CycleClock tells you the current time in Cycles. The "time"
// is actually time since power-on. This is like time() but doesn't
// involve a system call and is much more precise.
// NOTE: Not all cpu/platform/kernel combinations guarantee that this
// clock increments at a constant rate or is synchronized across all logical
// cpus in a system.
// If you need the above guarantees, please consider using a different
// API. There are efforts to provide an interface which provides a millisecond
// granularity and implemented as a memory read. A memory read is generally
// cheaper than the CycleClock for many architectures.
// Also, in some out of order CPU implementations, the CycleClock is not
// serializing. So if you're trying to count at cycles granularity, your
// data might be inaccurate due to out of order instruction execution.
// ----------------------------------------------------------------------
#include <cstdint>
#include "benchmark/macros.h"
#include "internal_macros.h"
#if defined(OS_MACOSX)
#include <mach/mach_time.h>
// For MSVC, we want to use '_asm rdtsc' when possible (since it works
// with even ancient MSVC compilers), and when not possible the
// __rdtsc intrinsic, declared in <intrin.h>. Unfortunately, in some
// environments, <windows.h> and <intrin.h> have conflicting
// declarations of some other intrinsics, breaking compilation.
// Therefore, we simply declare __rdtsc ourselves. See also
#if defined(COMPILER_MSVC) && !defined(_M_IX86)
extern "C" uint64_t __rdtsc();
#pragma intrinsic(__rdtsc)
#include <sys/time.h>
namespace benchmark {
// NOTE: only i386 and x86_64 have been well tested.
// PPC, sparc, alpha, and ia64 are based on
// with modifications by m3b. See also
namespace cycleclock {
// This should return the number of cycles since power-on. Thread-safe.
inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
#if defined(OS_MACOSX)
// this goes at the top because we need ALL Macs, regardless of
// architecture, to return the number of "mach time units" that
// have passed since startup. See where
// InitializeSystemInfo() sets the supposed cpu clock frequency of
// macs to the number of mach time units per second, not actual
// CPU clock frequency (which can change in the face of CPU
// frequency scaling). Also note that when the Mac sleeps, this
// counter pauses; it does not continue counting, nor does it
// reset to zero.
return mach_absolute_time();
#elif defined(__i386__)
int64_t ret;
__asm__ volatile("rdtsc" : "=A"(ret));
return ret;
#elif defined(__x86_64__) || defined(__amd64__)
uint64_t low, high;
__asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
return (high << 32) | low;
#elif defined(__powerpc__) || defined(__ppc__)
// This returns a time-base, which is not always precisely a cycle-count.
int64_t tbl, tbu0, tbu1;
asm("mftbu %0" : "=r"(tbu0));
asm("mftb %0" : "=r"(tbl));
asm("mftbu %0" : "=r"(tbu1));
tbl &= -static_cast<int64>(tbu0 == tbu1);
// high 32 bits in tbu1; low 32 bits in tbl (tbu0 is garbage)
return (tbu1 << 32) | tbl;
#elif defined(__sparc__)
int64_t tick;
asm(".byte 0x83, 0x41, 0x00, 0x00");
asm("mov %%g1, %0" : "=r"(tick));
return tick;
#elif defined(__ia64__)
int64_t itc;
asm("mov %0 = ar.itc" : "=r"(itc));
return itc;
#elif defined(COMPILER_MSVC) && defined(_M_IX86)
// Older MSVC compilers (like 7.x) don't seem to support the
// __rdtsc intrinsic properly, so I prefer to use _asm instead
// when I know it will work. Otherwise, I'll use __rdtsc and hope
// the code is being compiled with a non-ancient compiler.
_asm rdtsc
#elif defined(COMPILER_MSVC)
return __rdtsc();
#elif defined(__ARM_ARCH)
#if (__ARM_ARCH >= 6) // V6 is the earliest arch that has a standard cyclecount
uint32_t pmccntr;
uint32_t pmuseren;
uint32_t pmcntenset;
// Read the user mode perf monitor counter access permissions.
asm("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
if (pmuseren & 1) { // Allows reading perfmon counters for user mode code.
asm("mrc p15, 0, %0, c9, c12, 1" : "=r"(pmcntenset));
if (pmcntenset & 0x80000000ul) { // Is it counting?
asm("mrc p15, 0, %0, c9, c13, 0" : "=r"(pmccntr));
// The counter is set up to count every 64th cycle
return static_cast<int64_t>(pmccntr) * 64; // Should optimize to << 6
struct timeval tv;
gettimeofday(&tv, nullptr);
return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
#elif defined(__mips__)
// mips apparently only allows rdtsc for superusers, so we fall
// back to gettimeofday. It's possible clock_gettime would be better.
struct timeval tv;
gettimeofday(&tv, nullptr);
return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
// The soft failover to a generic implementation is automatic only for ARM.
// For other platforms the developer is expected to make an attempt to create
// a fast implementation and use generic version if nothing better is available.
#error You need to define CycleTimer for your OS and CPU
} // end namespace cycleclock
} // end namespace benchmark