tools/llvm-exegesis/lib/PerfHelper.h

//===-- PerfHelper.h ------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Helpers for measuring perf events.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
#define LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H

#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Config/config.h"
#include "llvm/Support/Error.h"

#include <cstdint>
#include <functional>
#include <memory>

struct perf_event_attr;

namespace llvm {
namespace exegesis {
namespace pfm {

// Returns true on error.
bool pfmInitialize();
void pfmTerminate();

// Retrieves the encoding for the event described by pfm_event_string.
// NOTE: pfm_initialize() must be called before creating PerfEvent objects.
class PerfEvent {
public:
  // http://perfmon2.sourceforge.net/manv4/libpfm.html
  // Events are expressed as strings. e.g. "INSTRUCTION_RETIRED"
  explicit PerfEvent(StringRef PfmEventString);

  PerfEvent(const PerfEvent &) = delete;
  PerfEvent(PerfEvent &&other);
  ~PerfEvent();

  // The pfm_event_string passed at construction time.
  StringRef name() const;

  // Whether the event was successfully created.
  bool valid() const;

  // The encoded event to be passed to the Kernel.
  const perf_event_attr *attribute() const;

  // The fully qualified name for the event.
  // e.g. "snb_ep::INSTRUCTION_RETIRED:e=0:i=0:c=0:t=0:u=1:k=0:mg=0:mh=1"
  StringRef getPfmEventString() const;

protected:
  PerfEvent() = default;
  std::string EventString;
  std::string FullQualifiedEventString;
  perf_event_attr *Attr;
};

// Uses a valid PerfEvent to configure the Kernel so we can measure the
// underlying event.
class Counter {
public:
  // event: the PerfEvent to measure.
  explicit Counter(PerfEvent &&event);

  Counter(const Counter &) = delete;
  Counter(Counter &&other) = default;

  virtual ~Counter();

  /// Starts the measurement of the event.
  virtual void start();

  /// Stops the measurement of the event.
  void stop();

  /// Returns the current value of the counter or -1 if it cannot be read.
  int64_t read() const;

  /// Returns the current value of the counter or error if it cannot be read.
  /// FunctionBytes: The benchmark function being executed.
  /// This is used to filter out the measurements to ensure they are only
  /// within the benchmarked code.
  /// If empty (or not specified), then no filtering will be done.
  /// Not all counters choose to use this.
  virtual llvm::Expected<llvm::SmallVector<int64_t, 4>>
  readOrError(StringRef FunctionBytes = StringRef()) const;

  virtual int numValues() const;

protected:
  PerfEvent Event;
#ifdef HAVE_LIBPFM
  int FileDescriptor = -1;
#endif
};

} // namespace pfm
} // namespace exegesis
} // namespace llvm

#endif // LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H