1 /* 2 * Copyright (c) 2010, 2011, 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_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP 26 #define SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP 27 28 #include "runtime/simpleThresholdPolicy.hpp" 29 30 #ifdef TIERED 31 class CompileTask; 32 class CompileQueue; 33 34 /* 35 * The system supports 5 execution levels: 36 * * level 0 - interpreter 37 * * level 1 - C1 with full optimization (no profiling) 38 * * level 2 - C1 with invocation and backedge counters 39 * * level 3 - C1 with full profiling (level 2 + MDO) 40 * * level 4 - C2 41 * 42 * Levels 0, 2 and 3 periodically notify the runtime about the current value of the counters 43 * (invocation counters and backedge counters). The frequency of these notifications is 44 * different at each level. These notifications are used by the policy to decide what transition 45 * to make. 46 * 47 * Execution starts at level 0 (interpreter), then the policy can decide either to compile the 48 * method at level 3 or level 2. The decision is based on the following factors: 49 * 1. The length of the C2 queue determines the next level. The observation is that level 2 50 * is generally faster than level 3 by about 30%, therefore we would want to minimize the time 51 * a method spends at level 3. We should only spend the time at level 3 that is necessary to get 52 * adequate profiling. So, if the C2 queue is long enough it is more beneficial to go first to 53 * level 2, because if we transitioned to level 3 we would be stuck there until our C2 compile 54 * request makes its way through the long queue. When the load on C2 recedes we are going to 55 * recompile at level 3 and start gathering profiling information. 56 * 2. The length of C1 queue is used to dynamically adjust the thresholds, so as to introduce 57 * additional filtering if the compiler is overloaded. The rationale is that by the time a 58 * method gets compiled it can become unused, so it doesn't make sense to put too much onto the 59 * queue. 60 * 61 * After profiling is completed at level 3 the transition is made to level 4. Again, the length 62 * of the C2 queue is used as a feedback to adjust the thresholds. 63 * 64 * After the first C1 compile some basic information is determined about the code like the number 65 * of the blocks and the number of the loops. Based on that it can be decided that a method 66 * is trivial and compiling it with C1 will yield the same code. In this case the method is 67 * compiled at level 1 instead of 4. 68 * 69 * We also support profiling at level 0. If C1 is slow enough to produce the level 3 version of 70 * the code and the C2 queue is sufficiently small we can decide to start profiling in the 71 * interpreter (and continue profiling in the compiled code once the level 3 version arrives). 72 * If the profiling at level 0 is fully completed before level 3 version is produced, a level 2 73 * version is compiled instead in order to run faster waiting for a level 4 version. 74 * 75 * Compile queues are implemented as priority queues - for each method in the queue we compute 76 * the event rate (the number of invocation and backedge counter increments per unit of time). 77 * When getting an element off the queue we pick the one with the largest rate. Maintaining the 78 * rate also allows us to remove stale methods (the ones that got on the queue but stopped 79 * being used shortly after that). 80 */ 81 82 /* Command line options: 83 * - Tier?InvokeNotifyFreqLog and Tier?BackedgeNotifyFreqLog control the frequency of method 84 * invocation and backedge notifications. Basically every n-th invocation or backedge a mutator thread 85 * makes a call into the runtime. 86 * 87 * - Tier?CompileThreshold, Tier?BackEdgeThreshold, Tier?MinInvocationThreshold control 88 * compilation thresholds. 89 * Level 2 thresholds are not used and are provided for option-compatibility and potential future use. 90 * Other thresholds work as follows: 91 * 92 * Transition from interpreter (level 0) to C1 with full profiling (level 3) happens when 93 * the following predicate is true (X is the level): 94 * 95 * i > TierXInvocationThreshold * s || (i > TierXMinInvocationThreshold * s && i + b > TierXCompileThreshold * s), 96 * 97 * where $i$ is the number of method invocations, $b$ number of backedges and $s$ is the scaling 98 * coefficient that will be discussed further. 99 * The intuition is to equalize the time that is spend profiling each method. 100 * The same predicate is used to control the transition from level 3 to level 4 (C2). It should be 101 * noted though that the thresholds are relative. Moreover i and b for the 0->3 transition come 102 * from methodOop and for 3->4 transition they come from MDO (since profiled invocations are 103 * counted separately). 104 * 105 * OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates. 106 * 107 * - Tier?LoadFeedback options are used to automatically scale the predicates described above depending 108 * on the compiler load. The scaling coefficients are computed as follows: 109 * 110 * s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1, 111 * 112 * where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X 113 * is the number of level X compiler threads. 114 * 115 * Basically these parameters describe how many methods should be in the compile queue 116 * per compiler thread before the scaling coefficient increases by one. 117 * 118 * This feedback provides the mechanism to automatically control the flow of compilation requests 119 * depending on the machine speed, mutator load and other external factors. 120 * 121 * - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop. 122 * Consider the following observation: a method compiled with full profiling (level 3) 123 * is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO). 124 * Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue 125 * gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues 126 * executing at level 3 for much longer time than is required by the predicate and at suboptimal speed. 127 * The idea is to dynamically change the behavior of the system in such a way that if a substantial 128 * load on C2 is detected we would first do the 0->2 transition allowing a method to run faster. 129 * And then when the load decreases to allow 2->3 transitions. 130 * 131 * Tier3Delay* parameters control this switching mechanism. 132 * Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy 133 * no longer does 0->3 transitions but does 0->2 transitions instead. 134 * Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue 135 * per compiler thread falls below the specified amount. 136 * The hysteresis is necessary to avoid jitter. 137 * 138 * - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue. 139 * Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to 140 * compile from the compile queue, we also can detect stale methods for which the rate has been 141 * 0 for some time in the same iteration. Stale methods can appear in the queue when an application 142 * abruptly changes its behavior. 143 * 144 * - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick 145 * to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything 146 * with pure c1. 147 * 148 * - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the 149 * 0->3 predicate are already exceeded by the given percentage but the level 3 version of the 150 * method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled 151 * version in time. This reduces the overall transition to level 4 and decreases the startup time. 152 * Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long 153 * these is not reason to start profiling prematurely. 154 * 155 * - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation. 156 * Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered 157 * to be zero if no events occurred in TieredRateUpdateMaxTime. 158 */ 159 160 161 class AdvancedThresholdPolicy : public SimpleThresholdPolicy { 162 jlong _start_time; 163 164 // Call and loop predicates determine whether a transition to a higher compilation 165 // level should be performed (pointers to predicate functions are passed to common(). 166 // Predicates also take compiler load into account. 167 typedef bool (AdvancedThresholdPolicy::*Predicate)(int i, int b, CompLevel cur_level); 168 bool call_predicate(int i, int b, CompLevel cur_level); 169 bool loop_predicate(int i, int b, CompLevel cur_level); 170 // Common transition function. Given a predicate determines if a method should transition to another level. 171 CompLevel common(Predicate p, methodOop method, CompLevel cur_level, bool disable_feedback = false); 172 // Transition functions. 173 // call_event determines if a method should be compiled at a different 174 // level with a regular invocation entry. 175 CompLevel call_event(methodOop method, CompLevel cur_level); 176 // loop_event checks if a method should be OSR compiled at a different 177 // level. 178 CompLevel loop_event(methodOop method, CompLevel cur_level); 179 // Has a method been long around? 180 // We don't remove old methods from the compile queue even if they have 181 // very low activity (see select_task()). 182 inline bool is_old(methodOop method); 183 // Was a given method inactive for a given number of milliseconds. 184 // If it is, we would remove it from the queue (see select_task()). 185 inline bool is_stale(jlong t, jlong timeout, methodOop m); 186 // Compute the weight of the method for the compilation scheduling 187 inline double weight(methodOop method); 188 // Apply heuristics and return true if x should be compiled before y 189 inline bool compare_methods(methodOop x, methodOop y); 190 // Compute event rate for a given method. The rate is the number of event (invocations + backedges) 191 // per millisecond. 192 inline void update_rate(jlong t, methodOop m); 193 // Compute threshold scaling coefficient 194 inline double threshold_scale(CompLevel level, int feedback_k); 195 // If a method is old enough and is still in the interpreter we would want to 196 // start profiling without waiting for the compiled method to arrive. This function 197 // determines whether we should do that. 198 inline bool should_create_mdo(methodOop method, CompLevel cur_level); 199 // Create MDO if necessary. 200 void create_mdo(methodHandle mh, TRAPS); 201 // Is method profiled enough? 202 bool is_method_profiled(methodOop method); 203 204 protected: 205 void print_specific(EventType type, methodHandle mh, methodHandle imh, int bci, CompLevel level); 206 207 void set_start_time(jlong t) { _start_time = t; } 208 jlong start_time() const { return _start_time; } 209 210 // Submit a given method for compilation (and update the rate). 211 virtual void submit_compile(methodHandle mh, int bci, CompLevel level, TRAPS); 212 // event() from SimpleThresholdPolicy would call these. 213 virtual void method_invocation_event(methodHandle method, methodHandle inlinee, 214 CompLevel level, nmethod* nm, TRAPS); 215 virtual void method_back_branch_event(methodHandle method, methodHandle inlinee, 216 int bci, CompLevel level, nmethod* nm, TRAPS); 217 public: 218 AdvancedThresholdPolicy() : _start_time(0) { } 219 // Select task is called by CompileBroker. We should return a task or NULL. 220 virtual CompileTask* select_task(CompileQueue* compile_queue); 221 virtual void initialize(); 222 virtual bool should_not_inline(ciEnv* env, ciMethod* callee); 223 224 }; 225 226 #endif // TIERED 227 228 #endif // SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP