1 //===- llvm/Support/TimeProfiler.h - Hierarchical Time Profiler -*- 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 // This provides lightweight and dependency-free machinery to trace execution
10 // time around arbitrary code. Two API flavors are available.
11 //
12 // The primary API uses a RAII object to trigger tracing:
13 //
14 // \code
15 // {
16 // TimeTraceScope scope("my_event_name");
17 // ...my code...
18 // }
19 // \endcode
20 //
21 // If the code to be profiled does not have a natural lexical scope then
22 // it is also possible to start and end events with respect to an implicit
23 // per-thread stack of profiling entries:
24 //
25 // \code
26 // timeTraceProfilerBegin("my_event_name");
27 // ...my code...
28 // timeTraceProfilerEnd(); // must be called on all control flow paths
29 // \endcode
30 //
31 // Time profiling entries can be given an arbitrary name and, optionally,
32 // an arbitrary 'detail' string. The resulting trace will include 'Total'
33 // entries summing the time spent for each name. Thus, it's best to choose
34 // names to be fairly generic, and rely on the detail field to capture
35 // everything else of interest.
36 //
37 // To avoid lifetime issues name and detail strings are copied into the event
38 // entries at their time of creation. Care should be taken to make string
39 // construction cheap to prevent 'Heisenperf' effects. In particular, the
40 // 'detail' argument may be a string-returning closure:
41 //
42 // \code
43 // int n;
44 // {
45 // TimeTraceScope scope("my_event_name",
46 // [n]() { return (Twine("x=") + Twine(n)).str(); });
47 // ...my code...
48 // }
49 // \endcode
50 // The closure will not be called if tracing is disabled. Otherwise, the
51 // resulting string will be directly moved into the entry.
52 //
53 // The main process should begin with a timeTraceProfilerInitialize, and
54 // finish with timeTraceProfileWrite and timeTraceProfilerCleanup calls.
55 // Each new thread should begin with a timeTraceProfilerInitialize, and
56 // finish with a timeTraceProfilerFinishThread call.
57 //
58 // Timestamps come from std::chrono::stable_clock. Note that threads need
59 // not see the same time from that clock, and the resolution may not be
60 // the best available.
61 //
62 // Currently, there are a number of compatible viewers:
63 // - chrome://tracing is the original chromium trace viewer.
64 // - http://ui.perfetto.dev is the replacement for the above, under active
65 // development by Google as part of the 'Perfetto' project.
66 // - https://www.speedscope.app/ has also been reported as an option.
67 //
68 // Future work:
69 // - Support akin to LLVM_DEBUG for runtime enable/disable of named tracing
70 // families for non-debug builds which wish to support optional tracing.
71 // - Evaluate the detail closures at profile write time to avoid
72 // stringification costs interfering with tracing.
73 //
74 //===----------------------------------------------------------------------===//
75
76 #ifndef LLVM_SUPPORT_TIMEPROFILER_H
77 #define LLVM_SUPPORT_TIMEPROFILER_H
78
79 #include "llvm/ADT/STLFunctionalExtras.h"
80 #include "llvm/Support/Error.h"
81
82 namespace llvm {
83
84 class raw_pwrite_stream;
85
86 struct TimeTraceProfiler;
87 TimeTraceProfiler *getTimeTraceProfilerInstance();
88
89 /// Initialize the time trace profiler.
90 /// This sets up the global \p TimeTraceProfilerInstance
91 /// variable to be the profiler instance.
92 void timeTraceProfilerInitialize(unsigned TimeTraceGranularity,
93 StringRef ProcName);
94
95 /// Cleanup the time trace profiler, if it was initialized.
96 void timeTraceProfilerCleanup();
97
98 /// Finish a time trace profiler running on a worker thread.
99 void timeTraceProfilerFinishThread();
100
101 /// Is the time trace profiler enabled, i.e. initialized?
timeTraceProfilerEnabled()102 inline bool timeTraceProfilerEnabled() {
103 return getTimeTraceProfilerInstance() != nullptr;
104 }
105
106 /// Write profiling data to output stream.
107 /// Data produced is JSON, in Chrome "Trace Event" format, see
108 /// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview
109 void timeTraceProfilerWrite(raw_pwrite_stream &OS);
110
111 /// Write profiling data to a file.
112 /// The function will write to \p PreferredFileName if provided, if not
113 /// then will write to \p FallbackFileName appending .time-trace.
114 /// Returns a StringError indicating a failure if the function is
115 /// unable to open the file for writing.
116 Error timeTraceProfilerWrite(StringRef PreferredFileName,
117 StringRef FallbackFileName);
118
119 /// Manually begin a time section, with the given \p Name and \p Detail.
120 /// Profiler copies the string data, so the pointers can be given into
121 /// temporaries. Time sections can be hierarchical; every Begin must have a
122 /// matching End pair but they can nest.
123 void timeTraceProfilerBegin(StringRef Name, StringRef Detail);
124 void timeTraceProfilerBegin(StringRef Name,
125 llvm::function_ref<std::string()> Detail);
126
127 /// Manually end the last time section.
128 void timeTraceProfilerEnd();
129
130 /// The TimeTraceScope is a helper class to call the begin and end functions
131 /// of the time trace profiler. When the object is constructed, it begins
132 /// the section; and when it is destroyed, it stops it. If the time profiler
133 /// is not initialized, the overhead is a single branch.
134 struct TimeTraceScope {
135
136 TimeTraceScope() = delete;
137 TimeTraceScope(const TimeTraceScope &) = delete;
138 TimeTraceScope &operator=(const TimeTraceScope &) = delete;
139 TimeTraceScope(TimeTraceScope &&) = delete;
140 TimeTraceScope &operator=(TimeTraceScope &&) = delete;
141
TimeTraceScopeTimeTraceScope142 TimeTraceScope(StringRef Name) {
143 if (getTimeTraceProfilerInstance() != nullptr)
144 timeTraceProfilerBegin(Name, StringRef(""));
145 }
TimeTraceScopeTimeTraceScope146 TimeTraceScope(StringRef Name, StringRef Detail) {
147 if (getTimeTraceProfilerInstance() != nullptr)
148 timeTraceProfilerBegin(Name, Detail);
149 }
TimeTraceScopeTimeTraceScope150 TimeTraceScope(StringRef Name, llvm::function_ref<std::string()> Detail) {
151 if (getTimeTraceProfilerInstance() != nullptr)
152 timeTraceProfilerBegin(Name, Detail);
153 }
~TimeTraceScopeTimeTraceScope154 ~TimeTraceScope() {
155 if (getTimeTraceProfilerInstance() != nullptr)
156 timeTraceProfilerEnd();
157 }
158 };
159
160 } // end namespace llvm
161
162 #endif
163