Mercurial > hg > truffle
comparison src/share/vm/runtime/advancedThresholdPolicy.hpp @ 2348:5d8f5a6dced7
7020403: Add AdvancedCompilationPolicy for tiered
Summary: This implements adaptive tiered compilation policy.
Reviewed-by: kvn, never
author | iveresov |
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date | Fri, 04 Mar 2011 15:14:16 -0800 |
parents | |
children | 97b64f73103b |
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2325:8c9c9ee30d71 | 2348:5d8f5a6dced7 |
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1 /* | |
2 * Copyright (c) 2010, 2011 Oracle and/or its affiliates. All rights reserved. | |
3 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. | |
4 */ | |
5 | |
6 #ifndef SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP | |
7 #define SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP | |
8 | |
9 #include "runtime/simpleThresholdPolicy.hpp" | |
10 | |
11 #ifdef TIERED | |
12 class CompileTask; | |
13 class CompileQueue; | |
14 | |
15 /* | |
16 * The system supports 5 execution levels: | |
17 * * level 0 - interpreter | |
18 * * level 1 - C1 with full optimization (no profiling) | |
19 * * level 2 - C1 with invocation and backedge counters | |
20 * * level 3 - C1 with full profiling (level 2 + MDO) | |
21 * * level 4 - C2 | |
22 * | |
23 * Levels 0, 2 and 3 periodically notify the runtime about the current value of the counters | |
24 * (invocation counters and backedge counters). The frequency of these notifications is | |
25 * different at each level. These notifications are used by the policy to decide what transition | |
26 * to make. | |
27 * | |
28 * Execution starts at level 0 (interpreter), then the policy can decide either to compile the | |
29 * method at level 3 or level 2. The decision is based on the following factors: | |
30 * 1. The length of the C2 queue determines the next level. The observation is that level 2 | |
31 * is generally faster than level 3 by about 30%, therefore we would want to minimize the time | |
32 * a method spends at level 3. We should only spend the time at level 3 that is necessary to get | |
33 * adequate profiling. So, if the C2 queue is long enough it is more beneficial to go first to | |
34 * level 2, because if we transitioned to level 3 we would be stuck there until our C2 compile | |
35 * request makes its way through the long queue. When the load on C2 recedes we are going to | |
36 * recompile at level 3 and start gathering profiling information. | |
37 * 2. The length of C1 queue is used to dynamically adjust the thresholds, so as to introduce | |
38 * additional filtering if the compiler is overloaded. The rationale is that by the time a | |
39 * method gets compiled it can become unused, so it doesn't make sense to put too much onto the | |
40 * queue. | |
41 * | |
42 * After profiling is completed at level 3 the transition is made to level 4. Again, the length | |
43 * of the C2 queue is used as a feedback to adjust the thresholds. | |
44 * | |
45 * After the first C1 compile some basic information is determined about the code like the number | |
46 * of the blocks and the number of the loops. Based on that it can be decided that a method | |
47 * is trivial and compiling it with C1 will yield the same code. In this case the method is | |
48 * compiled at level 1 instead of 4. | |
49 * | |
50 * We also support profiling at level 0. If C1 is slow enough to produce the level 3 version of | |
51 * the code and the C2 queue is sufficiently small we can decide to start profiling in the | |
52 * interpreter (and continue profiling in the compiled code once the level 3 version arrives). | |
53 * If the profiling at level 0 is fully completed before level 3 version is produced, a level 2 | |
54 * version is compiled instead in order to run faster waiting for a level 4 version. | |
55 * | |
56 * Compile queues are implemented as priority queues - for each method in the queue we compute | |
57 * the event rate (the number of invocation and backedge counter increments per unit of time). | |
58 * When getting an element off the queue we pick the one with the largest rate. Maintaining the | |
59 * rate also allows us to remove stale methods (the ones that got on the queue but stopped | |
60 * being used shortly after that). | |
61 */ | |
62 | |
63 /* Command line options: | |
64 * - Tier?InvokeNotifyFreqLog and Tier?BackedgeNotifyFreqLog control the frequency of method | |
65 * invocation and backedge notifications. Basically every n-th invocation or backedge a mutator thread | |
66 * makes a call into the runtime. | |
67 * | |
68 * - Tier?CompileThreshold, Tier?BackEdgeThreshold, Tier?MinInvocationThreshold control | |
69 * compilation thresholds. | |
70 * Level 2 thresholds are not used and are provided for option-compatibility and potential future use. | |
71 * Other thresholds work as follows: | |
72 * | |
73 * Transition from interpreter (level 0) to C1 with full profiling (level 3) happens when | |
74 * the following predicate is true (X is the level): | |
75 * | |
76 * i > TierXInvocationThreshold * s || (i > TierXMinInvocationThreshold * s && i + b > TierXCompileThreshold * s), | |
77 * | |
78 * where $i$ is the number of method invocations, $b$ number of backedges and $s$ is the scaling | |
79 * coefficient that will be discussed further. | |
80 * The intuition is to equalize the time that is spend profiling each method. | |
81 * The same predicate is used to control the transition from level 3 to level 4 (C2). It should be | |
82 * noted though that the thresholds are relative. Moreover i and b for the 0->3 transition come | |
83 * from methodOop and for 3->4 transition they come from MDO (since profiled invocations are | |
84 * counted separately). | |
85 * | |
86 * OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates. | |
87 * | |
88 * - Tier?LoadFeedback options are used to automatically scale the predicates described above depending | |
89 * on the compiler load. The scaling coefficients are computed as follows: | |
90 * | |
91 * s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1, | |
92 * | |
93 * where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X | |
94 * is the number of level X compiler threads. | |
95 * | |
96 * Basically these parameters describe how many methods should be in the compile queue | |
97 * per compiler thread before the scaling coefficient increases by one. | |
98 * | |
99 * This feedback provides the mechanism to automatically control the flow of compilation requests | |
100 * depending on the machine speed, mutator load and other external factors. | |
101 * | |
102 * - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop. | |
103 * Consider the following observation: a method compiled with full profiling (level 3) | |
104 * is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO). | |
105 * Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue | |
106 * gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues | |
107 * executing at level 3 for much longer time than is required by the predicate and at suboptimal speed. | |
108 * The idea is to dynamically change the behavior of the system in such a way that if a substantial | |
109 * load on C2 is detected we would first do the 0->2 transition allowing a method to run faster. | |
110 * And then when the load decreases to allow 2->3 transitions. | |
111 * | |
112 * Tier3Delay* parameters control this switching mechanism. | |
113 * Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy | |
114 * no longer does 0->3 transitions but does 0->2 transitions instead. | |
115 * Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue | |
116 * per compiler thread falls below the specified amount. | |
117 * The hysteresis is necessary to avoid jitter. | |
118 * | |
119 * - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue. | |
120 * Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to | |
121 * compile from the compile queue, we also can detect stale methods for which the rate has been | |
122 * 0 for some time in the same iteration. Stale methods can appear in the queue when an application | |
123 * abruptly changes its behavior. | |
124 * | |
125 * - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick | |
126 * to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything | |
127 * with pure c1. | |
128 * | |
129 * - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the | |
130 * 0->3 predicate are already exceeded by the given percentage but the level 3 version of the | |
131 * method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled | |
132 * version in time. This reduces the overall transition to level 4 and decreases the startup time. | |
133 * Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long | |
134 * these is not reason to start profiling prematurely. | |
135 * | |
136 * - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation. | |
137 * Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered | |
138 * to be zero if no events occurred in TieredRateUpdateMaxTime. | |
139 */ | |
140 | |
141 | |
142 class AdvancedThresholdPolicy : public SimpleThresholdPolicy { | |
143 jlong _start_time; | |
144 | |
145 // Call and loop predicates determine whether a transition to a higher compilation | |
146 // level should be performed (pointers to predicate functions are passed to common(). | |
147 // Predicates also take compiler load into account. | |
148 typedef bool (AdvancedThresholdPolicy::*Predicate)(int i, int b, CompLevel cur_level); | |
149 bool call_predicate(int i, int b, CompLevel cur_level); | |
150 bool loop_predicate(int i, int b, CompLevel cur_level); | |
151 // Common transition function. Given a predicate determines if a method should transition to another level. | |
152 CompLevel common(Predicate p, methodOop method, CompLevel cur_level); | |
153 // Transition functions. | |
154 // call_event determines if a method should be compiled at a different | |
155 // level with a regular invocation entry. | |
156 CompLevel call_event(methodOop method, CompLevel cur_level); | |
157 // loop_event checks if a method should be OSR compiled at a different | |
158 // level. | |
159 CompLevel loop_event(methodOop method, CompLevel cur_level); | |
160 // Has a method been long around? | |
161 // We don't remove old methods from the compile queue even if they have | |
162 // very low activity (see select_task()). | |
163 inline bool is_old(methodOop method); | |
164 // Was a given method inactive for a given number of milliseconds. | |
165 // If it is, we would remove it from the queue (see select_task()). | |
166 inline bool is_stale(jlong t, jlong timeout, methodOop m); | |
167 // Compute the weight of the method for the compilation scheduling | |
168 inline double weight(methodOop method); | |
169 // Apply heuristics and return true if x should be compiled before y | |
170 inline bool compare_methods(methodOop x, methodOop y); | |
171 // Compute event rate for a given method. The rate is the number of event (invocations + backedges) | |
172 // per millisecond. | |
173 inline void update_rate(jlong t, methodOop m); | |
174 // Compute threshold scaling coefficient | |
175 inline double threshold_scale(CompLevel level, int feedback_k); | |
176 // If a method is old enough and is still in the interpreter we would want to | |
177 // start profiling without waiting for the compiled method to arrive. This function | |
178 // determines whether we should do that. | |
179 inline bool should_create_mdo(methodOop method, CompLevel cur_level); | |
180 // Create MDO if necessary. | |
181 void create_mdo(methodHandle mh, TRAPS); | |
182 // Is method profiled enough? | |
183 bool is_method_profiled(methodOop method); | |
184 | |
185 protected: | |
186 void print_specific(EventType type, methodHandle mh, methodHandle imh, int bci, CompLevel level); | |
187 | |
188 void set_start_time(jlong t) { _start_time = t; } | |
189 jlong start_time() const { return _start_time; } | |
190 | |
191 // Submit a given method for compilation (and update the rate). | |
192 virtual void submit_compile(methodHandle mh, int bci, CompLevel level, TRAPS); | |
193 // event() from SimpleThresholdPolicy would call these. | |
194 virtual void method_invocation_event(methodHandle method, methodHandle inlinee, | |
195 CompLevel level, TRAPS); | |
196 virtual void method_back_branch_event(methodHandle method, methodHandle inlinee, | |
197 int bci, CompLevel level, TRAPS); | |
198 public: | |
199 AdvancedThresholdPolicy() : _start_time(0) { } | |
200 // Select task is called by CompileBroker. We should return a task or NULL. | |
201 virtual CompileTask* select_task(CompileQueue* compile_queue); | |
202 virtual void initialize(); | |
203 }; | |
204 | |
205 #endif // TIERED | |
206 | |
207 #endif // SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP |