tools/llvm-exegesis/lib/PerfHelper.h

   1 //===-- PerfHelper.h ------------------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 ///
   9 /// \file
  10 /// Helpers for measuring perf events.
  11 ///
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
  15 #define LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
  16
  17 #include "llvm/ADT/ArrayRef.h"
  18 #include "llvm/ADT/StringRef.h"
  19 #include "llvm/Config/config.h"
  20 #include <functional>
  21 #include <memory>
  22
  23 struct perf_event_attr;
  24
  25 namespace llvm {
  26 namespace exegesis {
  27 namespace pfm {
  28
  29 // Returns true on error.
  30 bool pfmInitialize();
  31 void pfmTerminate();
  32
  33 // Retrieves the encoding for the event described by pfm_event_string.
  34 // NOTE: pfm_initialize() must be called before creating PerfEvent objects.
  35 class PerfEvent {
  36 public:
  37   // http://perfmon2.sourceforge.net/manv4/libpfm.html
  38   // Events are expressed as strings. e.g. "INSTRUCTION_RETIRED"
  39   explicit PerfEvent(llvm::StringRef pfm_event_string);
  40
  41   PerfEvent(const PerfEvent &) = delete;
  42   PerfEvent(PerfEvent &&other);
  43   ~PerfEvent();
  44
  45   // The pfm_event_string passed at construction time.
  46   llvm::StringRef name() const;
  47
  48   // Whether the event was successfully created.
  49   bool valid() const;
  50
  51   // The encoded event to be passed to the Kernel.
  52   const perf_event_attr *attribute() const;
  53
  54   // The fully qualified name for the event.
  55   // e.g. "snb_ep::INSTRUCTION_RETIRED:e=0:i=0:c=0:t=0:u=1:k=0:mg=0:mh=1"
  56   llvm::StringRef getPfmEventString() const;
  57
  58 private:
  59   const std::string EventString;
  60   std::string FullQualifiedEventString;
  61   perf_event_attr *Attr;
  62 };
  63
  64 // Uses a valid PerfEvent to configure the Kernel so we can measure the
  65 // underlying event.
  66 struct Counter {
  67   // event: the PerfEvent to measure.
  68   explicit Counter(const PerfEvent &event);
  69
  70   Counter(const Counter &) = delete;
  71   Counter(Counter &&other) = default;
  72
  73   ~Counter();
  74
  75   void start();         // Starts the measurement of the event.
  76   void stop();          // Stops the measurement of the event.
  77   int64_t read() const; // Return the current value of the counter.
  78
  79 private:
  80 #ifdef HAVE_LIBPFM
  81   int FileDescriptor = -1;
  82 #endif
  83 };
  84
  85 // Helper to measure a list of PerfEvent for a particular function.
  86 // callback is called for each successful measure (PerfEvent needs to be valid).
  87 template <typename Function>
  88 void Measure(
  89     llvm::ArrayRef<PerfEvent> Events,
  90     const std::function<void(const PerfEvent &Event, int64_t Value)> &Callback,
  91     Function Fn) {
  92   for (const auto &Event : Events) {
  93     if (!Event.valid())
  94       continue;
  95     Counter Cnt(Event);
  96     Cnt.start();
  97     Fn();
  98     Cnt.stop();
  99     Callback(Event, Cnt.read());
 100   }
 101 }
 102
 103 } // namespace pfm
 104 } // namespace exegesis
 105 } // namespace llvm
 106
 107 #endif // LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H