1 // ----------------------------------------------------------------------
2 // CycleClock
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.
6 //
7 // NOTE: Not all cpu/platform/kernel combinations guarantee that this
8 // clock increments at a constant rate or is synchronized across all logical
9 // cpus in a system.
10 //
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.
15 //
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 // ----------------------------------------------------------------------
20
21 #ifndef BENCHMARK_CYCLECLOCK_H_
22 #define BENCHMARK_CYCLECLOCK_H_
23
24 #include <cstdint>
25
26 #include "benchmark/benchmark.h"
27 #include "internal_macros.h"
28
29 #if defined(BENCHMARK_OS_MACOSX)
30 #include <mach/mach_time.h>
31 #endif
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) && !defined(_M_ARM64) && \
40 !defined(_M_ARM64EC)
41 extern "C" uint64_t __rdtsc();
42 #pragma intrinsic(__rdtsc)
43 #endif
44
45 #if !defined(BENCHMARK_OS_WINDOWS) || defined(BENCHMARK_OS_MINGW)
46 #include <sys/time.h>
47 #include <time.h>
48 #endif
49
50 #ifdef BENCHMARK_OS_EMSCRIPTEN
51 #include <emscripten.h>
52 #endif
53
54 namespace benchmark {
55 // NOTE: only i386 and x86_64 have been well tested.
56 // PPC, sparc, alpha, and ia64 are based on
57 // http://peter.kuscsik.com/wordpress/?p=14
58 // with modifications by m3b. See also
59 // https://setisvn.ssl.berkeley.edu/svn/lib/fftw-3.0.1/kernel/cycle.h
60 namespace cycleclock {
61 // This should return the number of cycles since power-on. Thread-safe.
Now()62 inline BENCHMARK_ALWAYS_INLINE int64_t Now() {
63 #if defined(BENCHMARK_OS_MACOSX)
64 // this goes at the top because we need ALL Macs, regardless of
65 // architecture, to return the number of "mach time units" that
66 // have passed since startup. See sysinfo.cc where
67 // InitializeSystemInfo() sets the supposed cpu clock frequency of
68 // macs to the number of mach time units per second, not actual
69 // CPU clock frequency (which can change in the face of CPU
70 // frequency scaling). Also note that when the Mac sleeps, this
71 // counter pauses; it does not continue counting, nor does it
72 // reset to zero.
73 return static_cast<int64_t>(mach_absolute_time());
74 #elif defined(BENCHMARK_OS_EMSCRIPTEN)
75 // this goes above x86-specific code because old versions of Emscripten
76 // define __x86_64__, although they have nothing to do with it.
77 return static_cast<int64_t>(emscripten_get_now() * 1e+6);
78 #elif defined(__i386__)
79 int64_t ret;
80 __asm__ volatile("rdtsc" : "=A"(ret));
81 return ret;
82 #elif defined(__x86_64__) || defined(__amd64__)
83 uint64_t low, high;
84 __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
85 return static_cast<int64_t>((high << 32) | low);
86 #elif defined(__powerpc__) || defined(__ppc__)
87 // This returns a time-base, which is not always precisely a cycle-count.
88 #if defined(__powerpc64__) || defined(__ppc64__)
89 int64_t tb;
90 asm volatile("mfspr %0, 268" : "=r"(tb));
91 return tb;
92 #else
93 uint32_t tbl, tbu0, tbu1;
94 asm volatile(
95 "mftbu %0\n"
96 "mftb %1\n"
97 "mftbu %2"
98 : "=r"(tbu0), "=r"(tbl), "=r"(tbu1));
99 tbl &= -static_cast<int32_t>(tbu0 == tbu1);
100 // high 32 bits in tbu1; low 32 bits in tbl (tbu0 is no longer needed)
101 return (static_cast<uint64_t>(tbu1) << 32) | tbl;
102 #endif
103 #elif defined(__sparc__)
104 int64_t tick;
105 asm(".byte 0x83, 0x41, 0x00, 0x00");
106 asm("mov %%g1, %0" : "=r"(tick));
107 return tick;
108 #elif defined(__ia64__)
109 int64_t itc;
110 asm("mov %0 = ar.itc" : "=r"(itc));
111 return itc;
112 #elif defined(COMPILER_MSVC) && defined(_M_IX86)
113 // Older MSVC compilers (like 7.x) don't seem to support the
114 // __rdtsc intrinsic properly, so I prefer to use _asm instead
115 // when I know it will work. Otherwise, I'll use __rdtsc and hope
116 // the code is being compiled with a non-ancient compiler.
117 _asm rdtsc
118 #elif defined(COMPILER_MSVC) && (defined(_M_ARM64) || defined(_M_ARM64EC))
119 // See // https://docs.microsoft.com/en-us/cpp/intrinsics/arm64-intrinsics
120 // and https://reviews.llvm.org/D53115
121 int64_t virtual_timer_value;
122 virtual_timer_value = _ReadStatusReg(ARM64_CNTVCT);
123 return virtual_timer_value;
124 #elif defined(COMPILER_MSVC)
125 return __rdtsc();
126 #elif defined(BENCHMARK_OS_NACL)
127 // Native Client validator on x86/x86-64 allows RDTSC instructions,
128 // and this case is handled above. Native Client validator on ARM
129 // rejects MRC instructions (used in the ARM-specific sequence below),
130 // so we handle it here. Portable Native Client compiles to
131 // architecture-agnostic bytecode, which doesn't provide any
132 // cycle counter access mnemonics.
133
134 // Native Client does not provide any API to access cycle counter.
135 // Use clock_gettime(CLOCK_MONOTONIC, ...) instead of gettimeofday
136 // because is provides nanosecond resolution (which is noticeable at
137 // least for PNaCl modules running on x86 Mac & Linux).
138 // Initialize to always return 0 if clock_gettime fails.
139 struct timespec ts = {0, 0};
140 clock_gettime(CLOCK_MONOTONIC, &ts);
141 return static_cast<int64_t>(ts.tv_sec) * 1000000000 + ts.tv_nsec;
142 #elif defined(__aarch64__)
143 // System timer of ARMv8 runs at a different frequency than the CPU's.
144 // The frequency is fixed, typically in the range 1-50MHz. It can be
145 // read at CNTFRQ special register. We assume the OS has set up
146 // the virtual timer properly.
147 int64_t virtual_timer_value;
148 asm volatile("mrs %0, cntvct_el0" : "=r"(virtual_timer_value));
149 return virtual_timer_value;
150 #elif defined(__ARM_ARCH)
151 // V6 is the earliest arch that has a standard cyclecount
152 // Native Client validator doesn't allow MRC instructions.
153 #if (__ARM_ARCH >= 6)
154 uint32_t pmccntr;
155 uint32_t pmuseren;
156 uint32_t pmcntenset;
157 // Read the user mode perf monitor counter access permissions.
158 asm volatile("mrc p15, 0, %0, c9, c14, 0" : "=r"(pmuseren));
159 if (pmuseren & 1) { // Allows reading perfmon counters for user mode code.
160 asm volatile("mrc p15, 0, %0, c9, c12, 1" : "=r"(pmcntenset));
161 if (pmcntenset & 0x80000000ul) { // Is it counting?
162 asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r"(pmccntr));
163 // The counter is set up to count every 64th cycle
164 return static_cast<int64_t>(pmccntr) * 64; // Should optimize to << 6
165 }
166 }
167 #endif
168 struct timeval tv;
169 gettimeofday(&tv, nullptr);
170 return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
171 #elif defined(__mips__) || defined(__m68k__)
172 // mips apparently only allows rdtsc for superusers, so we fall
173 // back to gettimeofday. It's possible clock_gettime would be better.
174 struct timeval tv;
175 gettimeofday(&tv, nullptr);
176 return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
177 #elif defined(__loongarch__) || defined(__csky__)
178 struct timeval tv;
179 gettimeofday(&tv, nullptr);
180 return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
181 #elif defined(__s390__) // Covers both s390 and s390x.
182 // Return the CPU clock.
183 uint64_t tsc;
184 #if defined(BENCHMARK_OS_ZOS)
185 // z/OS HLASM syntax.
186 asm(" stck %0" : "=m"(tsc) : : "cc");
187 #else
188 // Linux on Z syntax.
189 asm("stck %0" : "=Q"(tsc) : : "cc");
190 #endif
191 return tsc;
192 #elif defined(__riscv) // RISC-V
193 // Use RDTIME (and RDTIMEH on riscv32).
194 // RDCYCLE is a privileged instruction since Linux 6.6.
195 #if __riscv_xlen == 32
196 uint32_t cycles_lo, cycles_hi0, cycles_hi1;
197 // This asm also includes the PowerPC overflow handling strategy, as above.
198 // Implemented in assembly because Clang insisted on branching.
199 asm volatile(
200 "rdtimeh %0\n"
201 "rdtime %1\n"
202 "rdtimeh %2\n"
203 "sub %0, %0, %2\n"
204 "seqz %0, %0\n"
205 "sub %0, zero, %0\n"
206 "and %1, %1, %0\n"
207 : "=r"(cycles_hi0), "=r"(cycles_lo), "=r"(cycles_hi1));
208 return static_cast<int64_t>((static_cast<uint64_t>(cycles_hi1) << 32) |
209 cycles_lo);
210 #else
211 uint64_t cycles;
212 asm volatile("rdtime %0" : "=r"(cycles));
213 return static_cast<int64_t>(cycles);
214 #endif
215 #elif defined(__e2k__) || defined(__elbrus__)
216 struct timeval tv;
217 gettimeofday(&tv, nullptr);
218 return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
219 #elif defined(__hexagon__)
220 uint64_t pcycle;
221 asm volatile("%0 = C15:14" : "=r"(pcycle));
222 return static_cast<double>(pcycle);
223 #elif defined(__alpha__)
224 // Alpha has a cycle counter, the PCC register, but it is an unsigned 32-bit
225 // integer and thus wraps every ~4s, making using it for tick counts
226 // unreliable beyond this time range. The real-time clock is low-precision,
227 // roughtly ~1ms, but it is the only option that can reasonable count
228 // indefinitely.
229 struct timeval tv;
230 gettimeofday(&tv, nullptr);
231 return static_cast<int64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
232 #else
233 // The soft failover to a generic implementation is automatic only for ARM.
234 // For other platforms the developer is expected to make an attempt to create
235 // a fast implementation and use generic version if nothing better is
236 // available.
237 #error You need to define CycleTimer for your OS and CPU
238 #endif
239 }
240 } // end namespace cycleclock
241 } // end namespace benchmark
242
243 #endif // BENCHMARK_CYCLECLOCK_H_
244