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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 <cstring>
#include <memory>
#include <vector>
#include "benchmark/benchmark.h"
#include "check.h"
#include "log.h"
#include "mutex.h"
#ifndef BENCHMARK_OS_WINDOWS
#include <unistd.h>
#endif
#if defined(_MSC_VER)
#pragma warning(push)
// C4251: <symbol> needs to have dll-interface to be used by clients of class
#pragma warning(disable : 4251)
#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 Read() method relocates individual reads, discarding
// the initial padding from each group leader in the values buffer such that
// all user accesses through the [] operator are correct.
class BENCHMARK_EXPORT PerfCounterValues {
public:
explicit PerfCounterValues(size_t nr_counters) : nr_counters_(nr_counters) {
BM_CHECK_LE(nr_counters_, kMaxCounters);
}
// We are reading correctly now so the values don't need to skip padding
uint64_t operator[](size_t pos) const { return values_[pos]; }
// Increased the maximum to 32 only since the buffer
// is std::array<> backed
static constexpr size_t kMaxCounters = 32;
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_)};
}
// This reading is complex and as the goal of this class is to
// abstract away the intrincacies of the reading process, this is
// a better place for it
size_t Read(const std::vector<int>& leaders);
// Move the padding to 2 due to the reading algorithm (1st padding plus a
// current read padding)
static constexpr size_t kPadding = 2;
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 BENCHMARK_EXPORT PerfCounters final {
public:
// True iff this platform supports performance counters.
static const bool kSupported;
// Returns an empty object
static PerfCounters NoCounters() { return PerfCounters(); }
~PerfCounters() { CloseCounters(); }
PerfCounters() = default;
PerfCounters(PerfCounters&&) = default;
PerfCounters(const PerfCounters&) = delete;
PerfCounters& operator=(PerfCounters&&) noexcept;
PerfCounters& operator=(const PerfCounters&) = delete;
// Platform-specific implementations may choose to do some library
// initialization here.
static bool Initialize();
// Check if the given counter is supported, if the app wants to
// check before passing
static bool IsCounterSupported(const std::string& name);
// 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.
// In case of failure, this method will in the worst case return an
// empty object whose state will still be valid.
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);
return values->Read(leader_ids_) == counter_ids_.size();
#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, std::vector<int>&& leader_ids)
: counter_ids_(std::move(counter_ids)),
leader_ids_(std::move(leader_ids)),
counter_names_(counter_names) {}
void CloseCounters() const;
std::vector<int> counter_ids_;
std::vector<int> leader_ids_;
std::vector<std::string> counter_names_;
};
// Typical usage of the above primitives.
class BENCHMARK_EXPORT PerfCountersMeasurement final {
public:
PerfCountersMeasurement(const std::vector<std::string>& counter_names);
size_t num_counters() const { return counters_.num_counters(); }
std::vector<std::string> names() const { return counters_.names(); }
BENCHMARK_ALWAYS_INLINE bool Start() {
if (num_counters() == 0) return true;
// Tell the compiler to not move instructions above/below where we take
// the snapshot.
ClobberMemory();
valid_read_ &= counters_.Snapshot(&start_values_);
ClobberMemory();
return valid_read_;
}
BENCHMARK_ALWAYS_INLINE bool Stop(
std::vector<std::pair<std::string, double>>& measurements) {
if (num_counters() == 0) return true;
// Tell the compiler to not move instructions above/below where we take
// the snapshot.
ClobberMemory();
valid_read_ &= counters_.Snapshot(&end_values_);
ClobberMemory();
for (size_t i = 0; i < counters_.names().size(); ++i) {
double measurement = static_cast<double>(end_values_[i]) -
static_cast<double>(start_values_[i]);
measurements.push_back({counters_.names()[i], measurement});
}
return valid_read_;
}
private:
PerfCounters counters_;
bool valid_read_ = true;
PerfCounterValues start_values_;
PerfCounterValues end_values_;
};
} // namespace internal
} // namespace benchmark
#if defined(_MSC_VER)
#pragma warning(pop)
#endif
#endif // BENCHMARK_PERF_COUNTERS_H
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