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thirdparty/basalt-headers/test/benchmark/src/perf_counters.h

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+// Copyright 2021 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef BENCHMARK_PERF_COUNTERS_H
+#define BENCHMARK_PERF_COUNTERS_H
+
+#include <array>
+#include <cstdint>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "check.h"
+#include "log.h"
+
+#ifndef BENCHMARK_OS_WINDOWS
+#include <unistd.h>
+#endif
+
+namespace benchmark {
+namespace internal {
+
+// Typically, we can only read a small number of counters. There is also a
+// padding preceding counter values, when reading multiple counters with one
+// syscall (which is desirable). PerfCounterValues abstracts these details.
+// The implementation ensures the storage is inlined, and allows 0-based
+// indexing into the counter values.
+// The object is used in conjunction with a PerfCounters object, by passing it
+// to Snapshot(). The values are populated such that
+// perfCounters->names()[i]'s value is obtained at position i (as given by
+// operator[]) of this object.
+class PerfCounterValues {
+ public:
+  explicit PerfCounterValues(size_t nr_counters) : nr_counters_(nr_counters) {
+    BM_CHECK_LE(nr_counters_, kMaxCounters);
+  }
+
+  uint64_t operator[](size_t pos) const { return values_[kPadding + pos]; }
+
+  static constexpr size_t kMaxCounters = 3;
+
+ private:
+  friend class PerfCounters;
+  // Get the byte buffer in which perf counters can be captured.
+  // This is used by PerfCounters::Read
+  std::pair<char*, size_t> get_data_buffer() {
+    return {reinterpret_cast<char*>(values_.data()),
+            sizeof(uint64_t) * (kPadding + nr_counters_)};
+  }
+
+  static constexpr size_t kPadding = 1;
+  std::array<uint64_t, kPadding + kMaxCounters> values_;
+  const size_t nr_counters_;
+};
+
+// Collect PMU counters. The object, once constructed, is ready to be used by
+// calling read(). PMU counter collection is enabled from the time create() is
+// called, to obtain the object, until the object's destructor is called.
+class PerfCounters final {
+ public:
+  // True iff this platform supports performance counters.
+  static const bool kSupported;
+
+  bool IsValid() const { return is_valid_; }
+  static PerfCounters NoCounters() { return PerfCounters(); }
+
+  ~PerfCounters();
+  PerfCounters(PerfCounters&&) = default;
+  PerfCounters(const PerfCounters&) = delete;
+
+  // Platform-specific implementations may choose to do some library
+  // initialization here.
+  static bool Initialize();
+
+  // Return a PerfCounters object ready to read the counters with the names
+  // specified. The values are user-mode only. The counter name format is
+  // implementation and OS specific.
+  // TODO: once we move to C++-17, this should be a std::optional, and then the
+  // IsValid() boolean can be dropped.
+  static PerfCounters Create(const std::vector<std::string>& counter_names);
+
+  // Take a snapshot of the current value of the counters into the provided
+  // valid PerfCounterValues storage. The values are populated such that:
+  // names()[i]'s value is (*values)[i]
+  BENCHMARK_ALWAYS_INLINE bool Snapshot(PerfCounterValues* values) const {
+#ifndef BENCHMARK_OS_WINDOWS
+    assert(values != nullptr);
+    assert(IsValid());
+    auto buffer = values->get_data_buffer();
+    auto read_bytes = ::read(counter_ids_[0], buffer.first, buffer.second);
+    return static_cast<size_t>(read_bytes) == buffer.second;
+#else
+    (void)values;
+    return false;
+#endif
+  }
+
+  const std::vector<std::string>& names() const { return counter_names_; }
+  size_t num_counters() const { return counter_names_.size(); }
+
+ private:
+  PerfCounters(const std::vector<std::string>& counter_names,
+               std::vector<int>&& counter_ids)
+      : counter_ids_(std::move(counter_ids)),
+        counter_names_(counter_names),
+        is_valid_(true) {}
+  PerfCounters() : is_valid_(false) {}
+
+  std::vector<int> counter_ids_;
+  const std::vector<std::string> counter_names_;
+  const bool is_valid_;
+};
+
+// Typical usage of the above primitives.
+class PerfCountersMeasurement final {
+ public:
+  PerfCountersMeasurement(PerfCounters&& c)
+      : counters_(std::move(c)),
+        start_values_(counters_.IsValid() ? counters_.names().size() : 0),
+        end_values_(counters_.IsValid() ? counters_.names().size() : 0) {}
+
+  bool IsValid() const { return counters_.IsValid(); }
+
+  BENCHMARK_ALWAYS_INLINE void Start() {
+    assert(IsValid());
+    // Tell the compiler to not move instructions above/below where we take
+    // the snapshot.
+    ClobberMemory();
+    counters_.Snapshot(&start_values_);
+    ClobberMemory();
+  }
+
+  BENCHMARK_ALWAYS_INLINE std::vector<std::pair<std::string, double>>
+  StopAndGetMeasurements() {
+    assert(IsValid());
+    // Tell the compiler to not move instructions above/below where we take
+    // the snapshot.
+    ClobberMemory();
+    counters_.Snapshot(&end_values_);
+    ClobberMemory();
+
+    std::vector<std::pair<std::string, double>> ret;
+    for (size_t i = 0; i < counters_.names().size(); ++i) {
+      double measurement = static_cast<double>(end_values_[i]) -
+                           static_cast<double>(start_values_[i]);
+      ret.push_back({counters_.names()[i], measurement});
+    }
+    return ret;
+  }
+
+ private:
+  PerfCounters counters_;
+  PerfCounterValues start_values_;
+  PerfCounterValues end_values_;
+};
+
+BENCHMARK_UNUSED static bool perf_init_anchor = PerfCounters::Initialize();
+
+}  // namespace internal
+}  // namespace benchmark
+
+#endif  // BENCHMARK_PERF_COUNTERS_H