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
82namespace llvm {
83
84class raw_pwrite_stream;
85
86struct TimeTraceMetadata {
87 std::string Detail;
88 // Source file and line number information for the event.
89 std::string File;
90 int Line = 0;
91
92 bool isEmpty() const { return Detail.empty() && File.empty(); }
93};
94
95struct TimeTraceProfiler;
96TimeTraceProfiler *getTimeTraceProfilerInstance();
97
98bool isTimeTraceVerbose();
99
100struct TimeTraceProfilerEntry;
101
102/// Initialize the time trace profiler.
103/// This sets up the global \p TimeTraceProfilerInstance
104/// variable to be the profiler instance.
105void timeTraceProfilerInitialize(unsigned TimeTraceGranularity,
106 StringRef ProcName,
107 bool TimeTraceVerbose = false);
108
109/// Cleanup the time trace profiler, if it was initialized.
110void timeTraceProfilerCleanup();
111
112/// Finish a time trace profiler running on a worker thread.
113void timeTraceProfilerFinishThread();
114
115/// Is the time trace profiler enabled, i.e. initialized?
116inline bool timeTraceProfilerEnabled() {
117 return getTimeTraceProfilerInstance() != nullptr;
118}
119
120/// Write profiling data to output stream.
121/// Data produced is JSON, in Chrome "Trace Event" format, see
122/// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview
123void timeTraceProfilerWrite(raw_pwrite_stream &OS);
124
125/// Write profiling data to a file.
126/// The function will write to \p PreferredFileName if provided, if not
127/// then will write to \p FallbackFileName appending .time-trace.
128/// Returns a StringError indicating a failure if the function is
129/// unable to open the file for writing.
130Error timeTraceProfilerWrite(StringRef PreferredFileName,
131 StringRef FallbackFileName);
132
133/// Manually begin a time section, with the given \p Name and \p Detail.
134/// Profiler copies the string data, so the pointers can be given into
135/// temporaries. Time sections can be hierarchical; every Begin must have a
136/// matching End pair but they can nest.
137TimeTraceProfilerEntry *timeTraceProfilerBegin(StringRef Name,
138 StringRef Detail);
139TimeTraceProfilerEntry *
140timeTraceProfilerBegin(StringRef Name,
141 llvm::function_ref<std::string()> Detail);
142
143TimeTraceProfilerEntry *
144timeTraceProfilerBegin(StringRef Name,
145 llvm::function_ref<TimeTraceMetadata()> MetaData);
146
147/// Manually begin a time section, with the given \p Name and \p Detail.
148/// This starts Async Events having \p Name as a category which is shown
149/// separately from other traces. See
150/// https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview#heading=h.jh64i9l3vwa1
151/// for more details.
152TimeTraceProfilerEntry *timeTraceAsyncProfilerBegin(StringRef Name,
153 StringRef Detail);
154
155/// Manually end the last time section.
156void timeTraceProfilerEnd();
157void timeTraceProfilerEnd(TimeTraceProfilerEntry *E);
158
159/// The TimeTraceScope is a helper class to call the begin and end functions
160/// of the time trace profiler. When the object is constructed, it begins
161/// the section; and when it is destroyed, it stops it. If the time profiler
162/// is not initialized, the overhead is a single branch.
163class TimeTraceScope {
164public:
165 TimeTraceScope() = delete;
166 TimeTraceScope(const TimeTraceScope &) = delete;
167 TimeTraceScope &operator=(const TimeTraceScope &) = delete;
168 TimeTraceScope(TimeTraceScope &&) = delete;
169 TimeTraceScope &operator=(TimeTraceScope &&) = delete;
170
171 TimeTraceScope(StringRef Name) {
172 if (getTimeTraceProfilerInstance() != nullptr)
173 Entry = timeTraceProfilerBegin(Name, Detail: StringRef(""));
174 }
175 TimeTraceScope(StringRef Name, StringRef Detail) {
176 if (getTimeTraceProfilerInstance() != nullptr)
177 Entry = timeTraceProfilerBegin(Name, Detail);
178 }
179 TimeTraceScope(StringRef Name, llvm::function_ref<std::string()> Detail) {
180 if (getTimeTraceProfilerInstance() != nullptr)
181 Entry = timeTraceProfilerBegin(Name, Detail);
182 }
183 TimeTraceScope(StringRef Name,
184 llvm::function_ref<TimeTraceMetadata()> Metadata) {
185 if (getTimeTraceProfilerInstance() != nullptr)
186 Entry = timeTraceProfilerBegin(Name, MetaData: Metadata);
187 }
188 ~TimeTraceScope() {
189 if (getTimeTraceProfilerInstance() != nullptr)
190 timeTraceProfilerEnd(E: Entry);
191 }
192
193private:
194 TimeTraceProfilerEntry *Entry = nullptr;
195};
196
197} // end namespace llvm
198
199#endif
200