1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
|
#pragma once
#include <stdint.h>
#include "Unroll.h"
// Platform-specific:
// - Per processor & compiler:
// - ReadTsc() reads the CPU's timestamp counter, returns int64_t
// - Per platform:
// - A type RealTime to abstract an absolute time point
// - ReadRealTime() to read a ReadTime value and write it to an address
// (there's a cross-plat overload that returns the time by value below)
// - operator- for RealTime returning an int64_t of ticks between two times
// - RealTimeTicksPerSecond() returning an int64_t
//
// Note: x86-64 Windows & POSIX only, so far. Other platforms/architectures TODO
namespace Timestamp {
#if defined(_MSC_VER) // MSVC
#include <intrin.h>
#if defined(_M_IX86) || defined(_M_X64)
inline int64_t ReadTsc() noexcept
{
_mm_lfence();
return (int64_t)__rdtsc();
}
#elif defined(_M_ARM) || defined(_M_ARM64)
#error "ARM architecture still needs implementation for Timestamp::ReadTsc in Timestamp.h"
#else
#error "Unknown architecture -- needs implementation for Timestamp::ReadTsc in Timestamp.h"
#endif
#elif defined(__GNUC__)// GCC and compatible
#include <x86intrin.h>
#if defined(__i386__) || defined(__x86_64__)
inline int64_t ReadTsc() noexcept
{
_mm_lfence();
return (int64_t)__rdtsc();
}
#elif defined(__arm__)
#error "ARM architecture still needs implementation for Timestamp::ReadTsc in Timestamp.h"
#else
#error "Unknown architecture -- needs implementation for Timestamp::ReadTsc in Timestamp.h"
#endif
#else // Other compilers
#error "Unknown compiler -- needs implementation for Timestamp::ReadTsc in Timestamp.h"
#endif
// Per-platform abstraction of RealTime, preferring a clock that is
// always fixed-rate over any that is affecting by time changes.
// For this reason, on Windows we choose QueryPerformanceCounter
// over GetSystemTimePreciseAsFileTime, and for POSIX clock_gettime
// we
#if _WIN32
#include <Windows.h>
using RealTime = LARGE_INTEGER;
inline void ReadRealTime(RealTime* pResult) noexcept
{
QueryPerformanceCounter(pResult);
}
int64_t operator-(RealTime const& lhs, RealTime const& rhs) noexcept
{
return (int64_t)lhs.QuadPart - (int64_t)rhs.QuadPart;
}
int64_t RealTimeTicksPerSecond() noexcept
{
LARGE_INTEGER qpf{};
QueryPerformanceFrequency(&qpf);
return (int64_t)qpf.QuadPart;
}
#else // POSIX
#include <time.h>
using RealTime = struct timespec;
inline void ReadRealTime(RealTime* pResult) noexcept
{
clock_gettime(CLOCK_MONOTONIC_RAW, pResult);
}
inline int64_t operator-(RealTime const& lhs, RealTime const& rhs) noexcept
{
int64_t secDiff = (int64_t)lhs.tv_sec - (int64_t)rhs.tv_sec;
int64_t nsecDiff = (int64_t)lhs.tv_nsec - (int64_t)rhs.tv_nsec;
return 1'000'000'000 * secDiff + nsecDiff;
}
inline int64_t RealTimeTicksPerSecond() noexcept
{
return 1'000'000'000;
}
#endif
// Helpful overload to return RealTime by value. All platform
// implementations are a direct pass-thru to the version that
// writes the result to an address, so this helper is the same
// across all platforms.
inline RealTime ReadRealTime() noexcept
{
RealTime time{};
ReadRealTime(&time);
return time;
}
class TscRateMeasurement
{
bool measured = false;
int64_t tscTicksPerSecond = 0; // Only valid to access when measured == true
int64_t tscStart = 0;
int64_t tscEnd = 0;
RealTime realTimeStart{};
RealTime realTimeEnd{};
double realTimeTicksPerSecond = 0;
public:
TscRateMeasurement() { Init(); }
void Init()
{
measured = false;
tscTicksPerSecond = 0;
realTimeTicksPerSecond = (double)RealTimeTicksPerSecond();
GetSyncPoint(tscStart, realTimeStart);
}
bool Update()
{
GetSyncPoint(tscEnd, realTimeEnd);
// Measurements only valid if enough time has elapsed since Init
// Assuming one second is sufficient
int64_t realTimeDiff = realTimeEnd - realTimeStart;
if (realTimeDiff > realTimeTicksPerSecond)
{
measured = true;
int64_t tscDiff = tscEnd - tscStart;
double tscTicksPerRealTimeTick = (double)tscDiff / (double)realTimeDiff;
tscTicksPerSecond = (int64_t)(tscTicksPerRealTimeTick * realTimeTicksPerSecond);
}
return measured;
}
bool Valid() const { return measured; }
int64_t TscTicksPerSecond() const
{
return measured ? tscTicksPerSecond : 0;
}
private:
static void GetSyncPoint(int64_t& tsc, RealTime& realTime)
__attribute__((noinline))
{
constexpr int sampleCount = 3;
int64_t tscVals[sampleCount + 1];
RealTime realTimeVals[sampleCount];
// unroll: for (int i = 0; i < sampleCount; ++i)
Unroll::For<0,sampleCount>::Do([&](int i)
{
tscVals[i] = ReadTsc();
ReadRealTime(&realTimeVals[i]);
});
tscVals[sampleCount] = ReadTsc();
int minDiffIndex = 0;
int64_t minDiff = tscVals[1] - tscVals[0];
for (int i = 1; i < sampleCount; ++i)
{
int64_t diff = tscVals[i + 1] - tscVals[i];
if (diff < minDiff)
{
minDiff = diff;
minDiffIndex = i;
}
}
realTime = realTimeVals[minDiffIndex];
tsc = (tscVals[minDiffIndex] + tscVals[minDiffIndex + 1]) / 2;
}
};
} // namespace Timestamp
|
