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 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 95 struct TimeTraceProfiler; 96 TimeTraceProfiler *getTimeTraceProfilerInstance(); 97 98 bool isTimeTraceVerbose(); 99 100 struct TimeTraceProfilerEntry; 101 102 /// Initialize the time trace profiler. 103 /// This sets up the global \p TimeTraceProfilerInstance 104 /// variable to be the profiler instance. 105 void timeTraceProfilerInitialize(unsigned TimeTraceGranularity, 106 StringRef ProcName, 107 bool TimeTraceVerbose = false); 108 109 /// Cleanup the time trace profiler, if it was initialized. 110 void timeTraceProfilerCleanup(); 111 112 /// Finish a time trace profiler running on a worker thread. 113 void timeTraceProfilerFinishThread(); 114 115 /// Is the time trace profiler enabled, i.e. initialized? 116 inline 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 123 void 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. 130 Error 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. 137 TimeTraceProfilerEntry *timeTraceProfilerBegin(StringRef Name, 138 StringRef Detail); 139 TimeTraceProfilerEntry * 140 timeTraceProfilerBegin(StringRef Name, 141 llvm::function_ref<std::string()> Detail); 142 143 TimeTraceProfilerEntry * 144 timeTraceProfilerBegin(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. 152 TimeTraceProfilerEntry *timeTraceAsyncProfilerBegin(StringRef Name, 153 StringRef Detail); 154 155 /// Manually end the last time section. 156 void timeTraceProfilerEnd(); 157 void 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. 163 class TimeTraceScope { 164 public: 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, 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); 187 } 188 ~TimeTraceScope() { 189 if (getTimeTraceProfilerInstance() != nullptr) 190 timeTraceProfilerEnd(Entry); 191 } 192 193 private: 194 TimeTraceProfilerEntry *Entry = nullptr; 195 }; 196 197 } // end namespace llvm 198 199 #endif 200