1 // Copyright 2021 Google Inc. All rights reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //     http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
15 #ifndef BENCHMARK_PERF_COUNTERS_H
16 #define BENCHMARK_PERF_COUNTERS_H
17 
18 #include <array>
19 #include <cstdint>
20 #include <vector>
21 
22 #include "benchmark/benchmark.h"
23 #include "check.h"
24 #include "log.h"
25 
26 #ifndef BENCHMARK_OS_WINDOWS
27 #include <unistd.h>
28 #endif
29 
30 namespace benchmark {
31 namespace internal {
32 
33 // Typically, we can only read a small number of counters. There is also a
34 // padding preceding counter values, when reading multiple counters with one
35 // syscall (which is desirable). PerfCounterValues abstracts these details.
36 // The implementation ensures the storage is inlined, and allows 0-based
37 // indexing into the counter values.
38 // The object is used in conjunction with a PerfCounters object, by passing it
39 // to Snapshot(). The values are populated such that
40 // perfCounters->names()[i]'s value is obtained at position i (as given by
41 // operator[]) of this object.
42 class PerfCounterValues {
43  public:
PerfCounterValues(size_t nr_counters)44   explicit PerfCounterValues(size_t nr_counters) : nr_counters_(nr_counters) {
45     BM_CHECK_LE(nr_counters_, kMaxCounters);
46   }
47 
48   uint64_t operator[](size_t pos) const { return values_[kPadding + pos]; }
49 
50   static constexpr size_t kMaxCounters = 3;
51 
52  private:
53   friend class PerfCounters;
54   // Get the byte buffer in which perf counters can be captured.
55   // This is used by PerfCounters::Read
get_data_buffer()56   std::pair<char*, size_t> get_data_buffer() {
57     return {reinterpret_cast<char*>(values_.data()),
58             sizeof(uint64_t) * (kPadding + nr_counters_)};
59   }
60 
61   static constexpr size_t kPadding = 1;
62   std::array<uint64_t, kPadding + kMaxCounters> values_;
63   const size_t nr_counters_;
64 };
65 
66 // Collect PMU counters. The object, once constructed, is ready to be used by
67 // calling read(). PMU counter collection is enabled from the time create() is
68 // called, to obtain the object, until the object's destructor is called.
69 class PerfCounters final {
70  public:
71   // True iff this platform supports performance counters.
72   static const bool kSupported;
73 
IsValid()74   bool IsValid() const { return is_valid_; }
NoCounters()75   static PerfCounters NoCounters() { return PerfCounters(); }
76 
77   ~PerfCounters();
78   PerfCounters(PerfCounters&&) = default;
79   PerfCounters(const PerfCounters&) = delete;
80 
81   // Platform-specific implementations may choose to do some library
82   // initialization here.
83   static bool Initialize();
84 
85   // Return a PerfCounters object ready to read the counters with the names
86   // specified. The values are user-mode only. The counter name format is
87   // implementation and OS specific.
88   // TODO: once we move to C++-17, this should be a std::optional, and then the
89   // IsValid() boolean can be dropped.
90   static PerfCounters Create(const std::vector<std::string>& counter_names);
91 
92   // Take a snapshot of the current value of the counters into the provided
93   // valid PerfCounterValues storage. The values are populated such that:
94   // names()[i]'s value is (*values)[i]
Snapshot(PerfCounterValues * values)95   BENCHMARK_ALWAYS_INLINE bool Snapshot(PerfCounterValues* values) const {
96 #ifndef BENCHMARK_OS_WINDOWS
97     assert(values != nullptr);
98     assert(IsValid());
99     auto buffer = values->get_data_buffer();
100     auto read_bytes = ::read(counter_ids_[0], buffer.first, buffer.second);
101     return static_cast<size_t>(read_bytes) == buffer.second;
102 #else
103     (void)values;
104     return false;
105 #endif
106   }
107 
names()108   const std::vector<std::string>& names() const { return counter_names_; }
num_counters()109   size_t num_counters() const { return counter_names_.size(); }
110 
111  private:
PerfCounters(const std::vector<std::string> & counter_names,std::vector<int> && counter_ids)112   PerfCounters(const std::vector<std::string>& counter_names,
113                std::vector<int>&& counter_ids)
114       : counter_ids_(std::move(counter_ids)),
115         counter_names_(counter_names),
116         is_valid_(true) {}
PerfCounters()117   PerfCounters() : is_valid_(false) {}
118 
119   std::vector<int> counter_ids_;
120   const std::vector<std::string> counter_names_;
121   const bool is_valid_;
122 };
123 
124 // Typical usage of the above primitives.
125 class PerfCountersMeasurement final {
126  public:
PerfCountersMeasurement(PerfCounters && c)127   PerfCountersMeasurement(PerfCounters&& c)
128       : counters_(std::move(c)),
129         start_values_(counters_.IsValid() ? counters_.names().size() : 0),
130         end_values_(counters_.IsValid() ? counters_.names().size() : 0) {}
131 
IsValid()132   bool IsValid() const { return counters_.IsValid(); }
133 
Start()134   BENCHMARK_ALWAYS_INLINE void Start() {
135     assert(IsValid());
136     // Tell the compiler to not move instructions above/below where we take
137     // the snapshot.
138     ClobberMemory();
139     counters_.Snapshot(&start_values_);
140     ClobberMemory();
141   }
142 
143   BENCHMARK_ALWAYS_INLINE std::vector<std::pair<std::string, double>>
StopAndGetMeasurements()144   StopAndGetMeasurements() {
145     assert(IsValid());
146     // Tell the compiler to not move instructions above/below where we take
147     // the snapshot.
148     ClobberMemory();
149     counters_.Snapshot(&end_values_);
150     ClobberMemory();
151 
152     std::vector<std::pair<std::string, double>> ret;
153     for (size_t i = 0; i < counters_.names().size(); ++i) {
154       double measurement = static_cast<double>(end_values_[i]) -
155                            static_cast<double>(start_values_[i]);
156       ret.push_back({counters_.names()[i], measurement});
157     }
158     return ret;
159   }
160 
161  private:
162   PerfCounters counters_;
163   PerfCounterValues start_values_;
164   PerfCounterValues end_values_;
165 };
166 
167 BENCHMARK_UNUSED static bool perf_init_anchor = PerfCounters::Initialize();
168 
169 }  // namespace internal
170 }  // namespace benchmark
171 
172 #endif  // BENCHMARK_PERF_COUNTERS_H
173