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/SmallVector.h"
19 #include "llvm/ADT/StringRef.h"
20 #include "llvm/Config/config.h"
21 #include "llvm/Support/Error.h"
22 
23 #include <cstdint>
24 #include <functional>
25 #include <memory>
26 
27 struct perf_event_attr;
28 
29 namespace llvm {
30 namespace exegesis {
31 namespace pfm {
32 
33 // Returns true on error.
34 bool pfmInitialize();
35 void pfmTerminate();
36 
37 // Retrieves the encoding for the event described by pfm_event_string.
38 // NOTE: pfm_initialize() must be called before creating PerfEvent objects.
39 class PerfEvent {
40 public:
41   // http://perfmon2.sourceforge.net/manv4/libpfm.html
42   // Events are expressed as strings. e.g. "INSTRUCTION_RETIRED"
43   explicit PerfEvent(StringRef PfmEventString);
44 
45   PerfEvent(const PerfEvent &) = delete;
46   PerfEvent(PerfEvent &&other);
47   ~PerfEvent();
48 
49   // The pfm_event_string passed at construction time.
50   StringRef name() const;
51 
52   // Whether the event was successfully created.
53   bool valid() const;
54 
55   // The encoded event to be passed to the Kernel.
56   const perf_event_attr *attribute() const;
57 
58   // The fully qualified name for the event.
59   // e.g. "snb_ep::INSTRUCTION_RETIRED:e=0:i=0:c=0:t=0:u=1:k=0:mg=0:mh=1"
60   StringRef getPfmEventString() const;
61 
62 protected:
63   PerfEvent() = default;
64   std::string EventString;
65   std::string FullQualifiedEventString;
66   perf_event_attr *Attr;
67 };
68 
69 // Uses a valid PerfEvent to configure the Kernel so we can measure the
70 // underlying event.
71 class Counter {
72 public:
73   // event: the PerfEvent to measure.
74   explicit Counter(PerfEvent &&event);
75 
76   Counter(const Counter &) = delete;
77   Counter(Counter &&other) = default;
78 
79   virtual ~Counter();
80 
81   /// Starts the measurement of the event.
82   virtual void start();
83 
84   /// Stops the measurement of the event.
85   void stop();
86 
87   /// Returns the current value of the counter or -1 if it cannot be read.
88   int64_t read() const;
89 
90   /// Returns the current value of the counter or error if it cannot be read.
91   /// FunctionBytes: The benchmark function being executed.
92   /// This is used to filter out the measurements to ensure they are only
93   /// within the benchmarked code.
94   /// If empty (or not specified), then no filtering will be done.
95   /// Not all counters choose to use this.
96   virtual llvm::Expected<llvm::SmallVector<int64_t, 4>>
97   readOrError(StringRef FunctionBytes = StringRef()) const;
98 
99   virtual int numValues() const;
100 
101 protected:
102   PerfEvent Event;
103 #ifdef HAVE_LIBPFM
104   int FileDescriptor = -1;
105 #endif
106 };
107 
108 } // namespace pfm
109 } // namespace exegesis
110 } // namespace llvm
111 
112 #endif // LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
113