1 // ----------------------------------------------------------------------
3 // A CycleClock tells you the current time in Cycles. The "time"
4 // is actually time since power-on. This is like time() but doesn't
5 // involve a system call and is much more precise.
7 // NOTE: Not all cpu/platform/kernel combinations guarantee that this
8 // clock increments at a constant rate or is synchronized across all logical
11 // If you need the above guarantees, please consider using a different
12 // API. There are efforts to provide an interface which provides a millisecond
13 // granularity and implemented as a memory read. A memory read is generally
14 // cheaper than the CycleClock for many architectures.
16 // Also, in some out of order CPU implementations, the CycleClock is not
17 // serializing. So if you're trying to count at cycles granularity, your
18 // data might be inaccurate due to out of order instruction execution.
19 // ----------------------------------------------------------------------
21 #ifndef BENCHMARK_CYCLECLOCK_H_
22 #define BENCHMARK_CYCLECLOCK_H_
26 #include "benchmark/macros.h"
27 #include "internal_macros.h"
29 #if defined(BENCHMARK_OS_MACOSX)
30 #include <mach/mach_time.h>
32 // For MSVC, we want to use '_asm rdtsc' when possible (since it works
33 // with even ancient MSVC compilers), and when not possible the
34 // __rdtsc intrinsic, declared in <intrin.h>. Unfortunately, in some
35 // environments, <windows.h> and <intrin.h> have conflicting
36 // declarations of some other intrinsics, breaking compilation.
37 // Therefore, we simply declare __rdtsc ourselves. See also
38 // http://connect.microsoft.com/VisualStudio/feedback/details/262047
39 #if defined(COMPILER_MSVC) && !defined(_M_IX86)
40 extern "C" uint64_t __rdtsc();
41 #pragma intrinsic(__rdtsc)
44 #ifndef BENCHMARK_OS_WINDOWS
49 // NOTE: only i386 and x86_64 have been well tested.
50 // PPC, sparc, alpha, and ia64 are based on
51 // http://peter.kuscsik.com/wordpress/?p=14
52 // with modifications by m3b. See also
53 // https://setisvn.ssl.berkeley.edu/svn/lib/fftw-3.0.1/kernel/cycle.h
54 namespace cycleclock {
55 // This should return the number of cycles since power-on. Thread-safe.
56 inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
57 #if defined(BENCHMARK_OS_MACOSX)
58 // this goes at the top because we need ALL Macs, regardless of
59 // architecture, to return the number of "mach time units" that
60 // have passed since startup. See sysinfo.cc where
61 // InitializeSystemInfo() sets the supposed cpu clock frequency of
62 // macs to the number of mach time units per second, not actual
63 // CPU clock frequency (which can change in the face of CPU
64 // frequency scaling). Also note that when the Mac sleeps, this
65 // counter pauses; it does not continue counting, nor does it
67 return mach_absolute_time();
68 #elif defined(__i386__)
70 __asm__ volatile("rdtsc" : "=A"(ret));
72 #elif defined(__x86_64__) || defined(__amd64__)
74 __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
75 return (high << 32) | low;
76 #elif defined(__powerpc__) || defined(__ppc__)
77 // This returns a time-base, which is not always precisely a cycle-count.
78 int64_t tbl, tbu0, tbu1;
79 asm("mftbu %0" : "=r"(tbu0));
80 asm("mftb %0" : "=r"(tbl));
81 asm("mftbu %0" : "=r"(tbu1));
82 tbl &= -static_cast<int64>(tbu0 == tbu1);
83 // high 32 bits in tbu1; low 32 bits in tbl (tbu0 is garbage)
84 return (tbu1 << 32) | tbl;
85 #elif defined(__sparc__)
87 asm(".byte 0x83, 0x41, 0x00, 0x00");
88 asm("mov %%g1, %0" : "=r"(tick));
90 #elif defined(__ia64__)
92 asm("mov %0 = ar.itc" : "=r"(itc));
94 #elif defined(COMPILER_MSVC) && defined(_M_IX86)
95 // Older MSVC compilers (like 7.x) don't seem to support the
96 // __rdtsc intrinsic properly, so I prefer to use _asm instead
97 // when I know it will work. Otherwise, I'll use __rdtsc and hope
98 // the code is being compiled with a non-ancient compiler.
100 #elif defined(COMPILER_MSVC)
102 #elif defined(__aarch64__)
103 // System timer of ARMv8 runs at a different frequency than the CPU's.
104 // The frequency is fixed, typically in the range 1-50MHz. It can be
105 // read at CNTFRQ special register. We assume the OS has set up
106 // the virtual timer properly.
107 int64_t virtual_timer_value;
108 asm volatile("mrs %0, cntvct_el0" : "=r"(virtual_timer_value));
109 return virtual_timer_value;
110 #elif defined(__ARM_ARCH)
111 #if (__ARM_ARCH >= 6) // V6 is the earliest arch that has a standard cyclecount
115 // Read the user mode perf monitor counter access permissions.
116 asm volatile("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
117 if (pmuseren & 1) { // Allows reading perfmon counters for user mode code.
118 asm volatile("mrc p15, 0, %0, c9, c12, 1" : "=r"(pmcntenset));
119 if (pmcntenset & 0x80000000ul) { // Is it counting?
120 asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(pmccntr));
121 // The counter is set up to count every 64th cycle
122 return static_cast<int64_t>(pmccntr) * 64; // Should optimize to << 6
127 gettimeofday(&tv, nullptr);
128 return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
129 #elif defined(__mips__)
130 // mips apparently only allows rdtsc for superusers, so we fall
131 // back to gettimeofday. It's possible clock_gettime would be better.
133 gettimeofday(&tv, nullptr);
134 return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
136 // The soft failover to a generic implementation is automatic only for ARM.
137 // For other platforms the developer is expected to make an attempt to create
138 // a fast implementation and use generic version if nothing better is available.
139 #error You need to define CycleTimer for your OS and CPU
142 } // end namespace cycleclock
143 } // end namespace benchmark
145 #endif // BENCHMARK_CYCLECLOCK_H_