1 /*
2 * Copyright (c) 2010, 2016, 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 *
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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?InvocationThreshold, 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 Method* and for 3->4 transition they come from MDO (since profiled invocations are
103 * counted separately). Finally, if a method does not contain anything worth profiling, a transition
104 * from level 3 to level 4 occurs without considering thresholds (e.g., with fewer invocations than
105 * what is specified by Tier4InvocationThreshold).
106 *
107 * OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates.
108 *
109 * - Tier?LoadFeedback options are used to automatically scale the predicates described above depending
110 * on the compiler load. The scaling coefficients are computed as follows:
111 *
112 * s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1,
113 *
114 * where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X
115 * is the number of level X compiler threads.
116 *
117 * Basically these parameters describe how many methods should be in the compile queue
118 * per compiler thread before the scaling coefficient increases by one.
119 *
120 * This feedback provides the mechanism to automatically control the flow of compilation requests
121 * depending on the machine speed, mutator load and other external factors.
122 *
123 * - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop.
124 * Consider the following observation: a method compiled with full profiling (level 3)
125 * is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO).
126 * Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue
127 * gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues
128 * executing at level 3 for much longer time than is required by the predicate and at suboptimal speed.
129 * The idea is to dynamically change the behavior of the system in such a way that if a substantial
130 * load on C2 is detected we would first do the 0->2 transition allowing a method to run faster.
131 * And then when the load decreases to allow 2->3 transitions.
132 *
133 * Tier3Delay* parameters control this switching mechanism.
134 * Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy
135 * no longer does 0->3 transitions but does 0->2 transitions instead.
136 * Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue
137 * per compiler thread falls below the specified amount.
138 * The hysteresis is necessary to avoid jitter.
139 *
140 * - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue.
141 * Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to
142 * compile from the compile queue, we also can detect stale methods for which the rate has been
143 * 0 for some time in the same iteration. Stale methods can appear in the queue when an application
144 * abruptly changes its behavior.
145 *
146 * - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick
147 * to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything
148 * with pure c1.
149 *
150 * - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the
151 * 0->3 predicate are already exceeded by the given percentage but the level 3 version of the
152 * method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled
153 * version in time. This reduces the overall transition to level 4 and decreases the startup time.
154 * Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long
155 * these is not reason to start profiling prematurely.
156 *
157 * - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation.
158 * Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered
159 * to be zero if no events occurred in TieredRateUpdateMaxTime.
160 */
161
162
163 class AdvancedThresholdPolicy : public SimpleThresholdPolicy {
164 jlong _start_time;
165
166 // Call and loop predicates determine whether a transition to a higher compilation
167 // level should be performed (pointers to predicate functions are passed to common().
168 // Predicates also take compiler load into account.
169 typedef bool (AdvancedThresholdPolicy::*Predicate)(int i, int b, CompLevel cur_level, Method* method);
170 bool call_predicate(int i, int b, CompLevel cur_level, Method* method);
171 bool loop_predicate(int i, int b, CompLevel cur_level, Method* method);
172 // Common transition function. Given a predicate determines if a method should transition to another level.
173 CompLevel common(Predicate p, Method* method, CompLevel cur_level, bool disable_feedback = false);
174 // Transition functions.
175 // call_event determines if a method should be compiled at a different
176 // level with a regular invocation entry.
177 CompLevel call_event(Method* method, CompLevel cur_level, JavaThread * thread);
178 // loop_event checks if a method should be OSR compiled at a different
179 // level.
180 CompLevel loop_event(Method* method, CompLevel cur_level, JavaThread * thread);
181 // Has a method been long around?
182 // We don't remove old methods from the compile queue even if they have
183 // very low activity (see select_task()).
184 inline bool is_old(Method* method);
185 // Was a given method inactive for a given number of milliseconds.
186 // If it is, we would remove it from the queue (see select_task()).
187 inline bool is_stale(jlong t, jlong timeout, Method* m);
188 // Compute the weight of the method for the compilation scheduling
189 inline double weight(Method* method);
190 // Apply heuristics and return true if x should be compiled before y
191 inline bool compare_methods(Method* x, Method* y);
192 // Compute event rate for a given method. The rate is the number of event (invocations + backedges)
193 // per millisecond.
194 inline void update_rate(jlong t, Method* m);
195 // Compute threshold scaling coefficient
196 inline double threshold_scale(CompLevel level, int feedback_k);
197 // If a method is old enough and is still in the interpreter we would want to
198 // start profiling without waiting for the compiled method to arrive. This function
199 // determines whether we should do that.
200 inline bool should_create_mdo(Method* method, CompLevel cur_level);
201 // Create MDO if necessary.
202 void create_mdo(methodHandle mh, JavaThread* thread);
203 // Is method profiled enough?
204 bool is_method_profiled(Method* method);
205
206 double _increase_threshold_at_ratio;
207
208 bool maybe_switch_to_aot(methodHandle mh, CompLevel cur_level, CompLevel next_level, JavaThread* thread);
209
210 protected:
211 void print_specific(EventType type, methodHandle mh, methodHandle imh, int bci, CompLevel level);
212
213 void set_increase_threshold_at_ratio() { _increase_threshold_at_ratio = 100 / (100 - (double)IncreaseFirstTierCompileThresholdAt); }
214 void set_start_time(jlong t) { _start_time = t; }
215 jlong start_time() const { return _start_time; }
216
217 // Submit a given method for compilation (and update the rate).
218 virtual void submit_compile(const methodHandle& mh, int bci, CompLevel level, JavaThread* thread);
219 // event() from SimpleThresholdPolicy would call these.
220 virtual void method_invocation_event(const methodHandle& method, const methodHandle& inlinee,
221 CompLevel level, CompiledMethod* nm, JavaThread* thread);
222 virtual void method_back_branch_event(const methodHandle& method, const methodHandle& inlinee,
223 int bci, CompLevel level, CompiledMethod* nm, JavaThread* thread);
224 public:
225 AdvancedThresholdPolicy() : _start_time(0) { }
226 // Select task is called by CompileBroker. We should return a task or NULL.
227 virtual CompileTask* select_task(CompileQueue* compile_queue);
228 virtual void initialize();
229 virtual bool should_not_inline(ciEnv* env, ciMethod* callee);
230
231 };
232
233 #endif // TIERED
234
235 #endif // SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP