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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
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