1 /* 2 * Copyright (c) 2010, 2025, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_COMPILER_COMPILATIONPOLICY_HPP 26 #define SHARE_COMPILER_COMPILATIONPOLICY_HPP 27 28 #include "code/nmethod.hpp" 29 #include "compiler/compileBroker.hpp" 30 #include "oops/methodData.hpp" 31 #include "oops/trainingData.hpp" 32 #include "utilities/globalDefinitions.hpp" 33 34 namespace CompilationPolicyUtils { 35 template<typename T> 36 class Queue { 37 class QueueNode : public CHeapObj<mtCompiler> { 38 T* _value; 39 QueueNode* _next; 40 public: 41 QueueNode(T* value, QueueNode* next) : _value(value), _next(next) { } 42 T* value() const { return _value; } 43 void set_next(QueueNode* next) { _next = next; } 44 QueueNode* next() const { return _next; } 45 }; 46 47 QueueNode* _head; 48 QueueNode* _tail; 49 int _processing; 50 51 void push_unlocked(T* value) { 52 QueueNode* n = new QueueNode(value, nullptr); 53 if (_tail != nullptr) { 54 _tail->set_next(n); 55 } 56 _tail = n; 57 if (_head == nullptr) { 58 _head = _tail; 59 } 60 } 61 T* pop_unlocked() { 62 QueueNode* n = _head; 63 if (_head != nullptr) { 64 _head = _head->next(); 65 } 66 if (_head == nullptr) { 67 _tail = _head; 68 } 69 T* value = nullptr; 70 if (n != nullptr) { 71 value = n->value(); 72 delete n; 73 } 74 return value; 75 } 76 public: 77 Queue() : _head(nullptr), _tail(nullptr) { } 78 void push(T* value, Monitor* lock, JavaThread* current) { 79 MonitorLocker locker(current, lock); 80 push_unlocked(value); 81 locker.notify_all(); 82 } 83 84 bool is_empty_unlocked() const { return _head == nullptr; } 85 bool is_processing_unlocked() const { return _processing > 0; } 86 87 T* pop(Monitor* lock, JavaThread* current) { 88 MonitorLocker locker(current, lock); 89 while (is_empty_unlocked() && !CompileBroker::is_compilation_disabled_forever()) { 90 locker.wait(); 91 } 92 T* value = pop_unlocked(); 93 return value; 94 } 95 96 T* try_pop(Monitor* lock, JavaThread* current) { 97 MonitorLocker locker(current, lock); 98 T* value = pop_unlocked(); 99 return value; 100 } 101 void print_on(outputStream* st); 102 }; 103 } // namespace CompilationPolicyUtils 104 105 class CompileTask; 106 class CompileQueue; 107 /* 108 * The system supports 5 execution levels: 109 * * level 0 - interpreter (Profiling is tracked by a MethodData object, or MDO in short) 110 * * level 1 - C1 with full optimization (no profiling) 111 * * level 2 - C1 with invocation and backedge counters 112 * * level 3 - C1 with full profiling (level 2 + All other MDO profiling information) 113 * * level 4 - C2 with full profile guided optimization 114 * 115 * The MethodData object is created by both the interpreter or either compiler to store any 116 * profiling information collected on a method (ciMethod::ensure_method_data() for C1 and C2 117 * and CompilationPolicy::create_mdo() for the interpreter). Both the interpreter and code 118 * compiled by C1 at level 3 will constantly update profiling information in the MDO during 119 * execution. The information in the MDO is then used by C1 and C2 during compilation, via 120 * the compiler interface (ciMethodXXX). 121 * See ciMethod.cpp and ciMethodData.cpp for information transfer from an MDO to the compilers 122 * through the compiler interface. 123 * 124 * Levels 0, 2 and 3 periodically notify the runtime about the current value of the counters 125 * (invocation counters and backedge counters). The frequency of these notifications is 126 * different at each level. These notifications are used by the policy to decide what transition 127 * to make. 128 * 129 * Execution starts at level 0 (interpreter), then the policy can decide either to compile the 130 * method at level 3 or level 2. The decision is based on the following factors: 131 * 1. The length of the C2 queue determines the next level. The observation is that level 2 132 * is generally faster than level 3 by about 30%, therefore we would want to minimize the time 133 * a method spends at level 3. We should only spend the time at level 3 that is necessary to get 134 * adequate profiling. So, if the C2 queue is long enough it is more beneficial to go first to 135 * level 2, because if we transitioned to level 3 we would be stuck there until our C2 compile 136 * request makes its way through the long queue. When the load on C2 recedes we are going to 137 * recompile at level 3 and start gathering profiling information. 138 * 2. The length of C1 queue is used to dynamically adjust the thresholds, so as to introduce 139 * additional filtering if the compiler is overloaded. The rationale is that by the time a 140 * method gets compiled it can become unused, so it doesn't make sense to put too much onto the 141 * queue. 142 * 143 * After profiling is completed at level 3 the transition is made to level 4. Again, the length 144 * of the C2 queue is used as a feedback to adjust the thresholds. 145 * 146 * After the first C1 compile some basic information is determined about the code like the number 147 * of the blocks and the number of the loops. Based on that it can be decided that a method 148 * is trivial and compiling it with C1 will yield the same code. In this case the method is 149 * compiled at level 1 instead of 4. 150 * 151 * We also support profiling at level 0. If C1 is slow enough to produce the level 3 version of 152 * the code and the C2 queue is sufficiently small we can decide to start profiling in the 153 * interpreter (and continue profiling in the compiled code once the level 3 version arrives). 154 * If the profiling at level 0 is fully completed before level 3 version is produced, a level 2 155 * version is compiled instead in order to run faster waiting for a level 4 version. 156 * 157 * Compile queues are implemented as priority queues - for each method in the queue we compute 158 * the event rate (the number of invocation and backedge counter increments per unit of time). 159 * When getting an element off the queue we pick the one with the largest rate. Maintaining the 160 * rate also allows us to remove stale methods (the ones that got on the queue but stopped 161 * being used shortly after that). 162 */ 163 164 /* Command line options: 165 * - Tier?InvokeNotifyFreqLog and Tier?BackedgeNotifyFreqLog control the frequency of method 166 * invocation and backedge notifications. Basically every n-th invocation or backedge a mutator thread 167 * makes a call into the runtime. 168 * 169 * - Tier?InvocationThreshold, Tier?CompileThreshold, Tier?BackEdgeThreshold, Tier?MinInvocationThreshold control 170 * compilation thresholds. 171 * Level 2 thresholds are not used and are provided for option-compatibility and potential future use. 172 * Other thresholds work as follows: 173 * 174 * Transition from interpreter (level 0) to C1 with full profiling (level 3) happens when 175 * the following predicate is true (X is the level): 176 * 177 * i > TierXInvocationThreshold * s || (i > TierXMinInvocationThreshold * s && i + b > TierXCompileThreshold * s), 178 * 179 * where $i$ is the number of method invocations, $b$ number of backedges and $s$ is the scaling 180 * coefficient that will be discussed further. 181 * The intuition is to equalize the time that is spend profiling each method. 182 * The same predicate is used to control the transition from level 3 to level 4 (C2). It should be 183 * noted though that the thresholds are relative. Moreover i and b for the 0->3 transition come 184 * from Method* and for 3->4 transition they come from MDO (since profiled invocations are 185 * counted separately). Finally, if a method does not contain anything worth profiling, a transition 186 * from level 3 to level 4 occurs without considering thresholds (e.g., with fewer invocations than 187 * what is specified by Tier4InvocationThreshold). 188 * 189 * OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates. 190 * 191 * - Tier?LoadFeedback options are used to automatically scale the predicates described above depending 192 * on the compiler load. The scaling coefficients are computed as follows: 193 * 194 * s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1, 195 * 196 * where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X 197 * is the number of level X compiler threads. 198 * 199 * Basically these parameters describe how many methods should be in the compile queue 200 * per compiler thread before the scaling coefficient increases by one. 201 * 202 * This feedback provides the mechanism to automatically control the flow of compilation requests 203 * depending on the machine speed, mutator load and other external factors. 204 * 205 * - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop. 206 * Consider the following observation: a method compiled with full profiling (level 3) 207 * is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO). 208 * Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue 209 * gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues 210 * executing at level 3 for much longer time than is required by the predicate and at suboptimal speed. 211 * The idea is to dynamically change the behavior of the system in such a way that if a substantial 212 * load on C2 is detected we would first do the 0->2 transition allowing a method to run faster. 213 * And then when the load decreases to allow 2->3 transitions. 214 * 215 * Tier3Delay* parameters control this switching mechanism. 216 * Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy 217 * no longer does 0->3 transitions but does 0->2 transitions instead. 218 * Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue 219 * per compiler thread falls below the specified amount. 220 * The hysteresis is necessary to avoid jitter. 221 * 222 * - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue. 223 * Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to 224 * compile from the compile queue, we also can detect stale methods for which the rate has been 225 * 0 for some time in the same iteration. Stale methods can appear in the queue when an application 226 * abruptly changes its behavior. 227 * 228 * - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick 229 * to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything 230 * with pure c1. 231 * 232 * - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the 233 * 0->3 predicate are already exceeded by the given percentage but the level 3 version of the 234 * method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled 235 * version in time. This reduces the overall transition to level 4 and decreases the startup time. 236 * Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long 237 * these is not reason to start profiling prematurely. 238 * 239 * - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation. 240 * Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered 241 * to be zero if no events occurred in TieredRateUpdateMaxTime. 242 */ 243 244 class CompilationPolicy : AllStatic { 245 friend class CallPredicate; 246 friend class LoopPredicate; 247 friend class RecompilationPolicy; 248 249 typedef CompilationPolicyUtils::Queue<InstanceKlass> TrainingReplayQueue; 250 251 static int64_t _start_time; 252 static int _c1_count, _c2_count, _ac_count; 253 static double _increase_threshold_at_ratio; 254 static TrainingReplayQueue _training_replay_queue; 255 256 // Set carry flags in the counters (in Method* and MDO). 257 inline static void handle_counter_overflow(const methodHandle& method); 258 #ifdef ASSERT 259 // Verify that a level is consistent with the compilation mode 260 static bool verify_level(CompLevel level); 261 #endif 262 // Clamp the request level according to various constraints. 263 inline static CompLevel limit_level(CompLevel level); 264 // Common transition function. Given a predicate determines if a method should transition to another level. 265 template<typename Predicate> 266 static CompLevel common(const methodHandle& method, CompLevel cur_level, JavaThread* THREAD, bool disable_feedback = false); 267 268 template<typename Predicate> 269 static CompLevel transition_from_none(const methodHandle& method, CompLevel cur_level, bool delay_profiling, bool disable_feedback); 270 template<typename Predicate> 271 static CompLevel transition_from_limited_profile(const methodHandle& method, CompLevel cur_level, bool delay_profiling, bool disable_feedback); 272 template<typename Predicate> 273 static CompLevel transition_from_full_profile(const methodHandle& method, CompLevel cur_level); 274 template<typename Predicate> 275 static CompLevel standard_transition(const methodHandle& method, CompLevel cur_level, bool delayprof, bool disable_feedback); 276 277 static CompLevel trained_transition_from_none(const methodHandle& method, CompLevel cur_level, MethodTrainingData* mtd, JavaThread* THREAD); 278 static CompLevel trained_transition_from_limited_profile(const methodHandle& method, CompLevel cur_level, MethodTrainingData* mtd, JavaThread* THREAD); 279 static CompLevel trained_transition_from_full_profile(const methodHandle& method, CompLevel cur_level, MethodTrainingData* mtd, JavaThread* THREAD); 280 static CompLevel trained_transition(const methodHandle& method, CompLevel cur_level, MethodTrainingData* mtd, JavaThread* THREAD); 281 282 // Transition functions. 283 // call_event determines if a method should be compiled at a different 284 // level with a regular invocation entry. 285 static CompLevel call_event(const methodHandle& method, CompLevel cur_level, JavaThread* THREAD); 286 // loop_event checks if a method should be OSR compiled at a different 287 // level. 288 static CompLevel loop_event(const methodHandle& method, CompLevel cur_level, JavaThread* THREAD); 289 static void print_counters_on(outputStream* st, const char* prefix, Method* m); 290 static void print_training_data_on(outputStream* st, const char* prefix, Method* method); 291 // Has a method been long around? 292 // We don't remove old methods from the compile queue even if they have 293 // very low activity (see select_task()). 294 inline static bool is_old(const methodHandle& method); 295 // Was a given method inactive for a given number of milliseconds. 296 // If it is, we would remove it from the queue (see select_task()). 297 inline static bool is_stale(int64_t t, int64_t timeout, const methodHandle& method); 298 // Compute the weight of the method for the compilation scheduling 299 inline static double weight(Method* method); 300 // Apply heuristics and return true if x should be compiled before y 301 inline static bool compare_methods(Method* x, Method* y); 302 inline static bool compare_tasks(CompileTask* x, CompileTask* y); 303 // Compute event rate for a given method. The rate is the number of event (invocations + backedges) 304 // per millisecond. 305 inline static void update_rate(int64_t t, const methodHandle& method); 306 // Compute threshold scaling coefficient 307 inline static double threshold_scale(CompLevel level, int feedback_k); 308 // If a method is old enough and is still in the interpreter we would want to 309 // start profiling without waiting for the compiled method to arrive. This function 310 // determines whether we should do that. 311 inline static bool should_create_mdo(const methodHandle& method, CompLevel cur_level); 312 // Create MDO if necessary. 313 static void create_mdo(const methodHandle& mh, JavaThread* THREAD); 314 // Is method profiled enough? 315 static bool is_method_profiled(const methodHandle& method); 316 317 static void set_c1_count(int x) { _c1_count = x; } 318 static void set_c2_count(int x) { _c2_count = x; } 319 static void set_ac_count(int x) { _ac_count = x; } 320 321 enum EventType { CALL, LOOP, COMPILE, FORCE_COMPILE, FORCE_RECOMPILE, REMOVE_FROM_QUEUE, UPDATE_IN_QUEUE, REPROFILE, MAKE_NOT_ENTRANT }; 322 static void print_event_on(outputStream *st, EventType type, Method* m, Method* im, int bci, CompLevel level); 323 static void print_event(EventType type, Method* m, Method* im, int bci, CompLevel level); 324 // Check if the method can be compiled, change level if necessary 325 static void compile(const methodHandle& mh, int bci, CompLevel level, TRAPS); 326 // Simple methods are as good being compiled with C1 as C2. 327 // This function tells if it's such a function. 328 inline static bool is_trivial(const methodHandle& method); 329 // Force method to be compiled at CompLevel_simple? 330 inline static bool force_comp_at_level_simple(const methodHandle& method); 331 332 // Get a compilation level for a given method. 333 static CompLevel comp_level(Method* method); 334 static void method_invocation_event(const methodHandle& method, const methodHandle& inlinee, 335 CompLevel level, nmethod* nm, TRAPS); 336 static void method_back_branch_event(const methodHandle& method, const methodHandle& inlinee, 337 int bci, CompLevel level, nmethod* nm, TRAPS); 338 339 static void set_increase_threshold_at_ratio() { _increase_threshold_at_ratio = 100 / (100 - (double)IncreaseFirstTierCompileThresholdAt); } 340 static void set_start_time(int64_t t) { _start_time = t; } 341 static int64_t start_time() { return _start_time; } 342 343 // m must be compiled before executing it 344 static bool must_be_compiled(const methodHandle& m, int comp_level = CompLevel_any); 345 static void maybe_compile_early(const methodHandle& m, TRAPS); 346 static void replay_training_at_init_impl(InstanceKlass* klass, JavaThread* current); 347 public: 348 static int min_invocations() { return Tier4MinInvocationThreshold; } 349 static int c1_count() { return _c1_count; } 350 static int c2_count() { return _c2_count; } 351 static int ac_count() { return _ac_count; } 352 static int compiler_count(CompLevel comp_level); 353 // If m must_be_compiled then request a compilation from the CompileBroker. 354 // This supports the -Xcomp option. 355 static void compile_if_required(const methodHandle& m, TRAPS); 356 357 static void replay_training_at_init(InstanceKlass* klass, JavaThread* current); 358 static void replay_training_at_init_loop(JavaThread* current); 359 360 // m is allowed to be compiled 361 static bool can_be_compiled(const methodHandle& m, int comp_level = CompLevel_any); 362 // m is allowed to be osr compiled 363 static bool can_be_osr_compiled(const methodHandle& m, int comp_level = CompLevel_any); 364 static bool is_compilation_enabled(); 365 366 static CompileTask* select_task_helper(CompileQueue* compile_queue); 367 // Return initial compile level to use with Xcomp (depends on compilation mode). 368 static void reprofile(ScopeDesc* trap_scope, bool is_osr); 369 static nmethod* event(const methodHandle& method, const methodHandle& inlinee, 370 int branch_bci, int bci, CompLevel comp_level, nmethod* nm, TRAPS); 371 // Select task is called by CompileBroker. We should return a task or nullptr. 372 static CompileTask* select_task(CompileQueue* compile_queue, JavaThread* THREAD); 373 // Tell the runtime if we think a given method is adequately profiled. 374 static bool is_mature(MethodData* mdo); 375 // Initialize: set compiler thread count 376 static void initialize(); 377 static bool should_not_inline(ciEnv* env, ciMethod* callee); 378 379 // Return desired initial compilation level for Xcomp 380 static CompLevel initial_compile_level(const methodHandle& method); 381 // Return highest level possible 382 static CompLevel highest_compile_level(); 383 static void dump(); 384 385 static void sample_load_average(); 386 static bool have_recompilation_work(); 387 static bool recompilation_step(int step, TRAPS); 388 }; 389 390 #endif // SHARE_COMPILER_COMPILATIONPOLICY_HPP