| /* |
| * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
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| */ |
| |
| #ifndef SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP |
| #define SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP |
| |
| #include "runtime/simpleThresholdPolicy.hpp" |
| |
| #ifdef TIERED |
| class CompileTask; |
| class CompileQueue; |
| |
| /* |
| * The system supports 5 execution levels: |
| * * level 0 - interpreter |
| * * level 1 - C1 with full optimization (no profiling) |
| * * level 2 - C1 with invocation and backedge counters |
| * * level 3 - C1 with full profiling (level 2 + MDO) |
| * * level 4 - C2 |
| * |
| * Levels 0, 2 and 3 periodically notify the runtime about the current value of the counters |
| * (invocation counters and backedge counters). The frequency of these notifications is |
| * different at each level. These notifications are used by the policy to decide what transition |
| * to make. |
| * |
| * Execution starts at level 0 (interpreter), then the policy can decide either to compile the |
| * method at level 3 or level 2. The decision is based on the following factors: |
| * 1. The length of the C2 queue determines the next level. The observation is that level 2 |
| * is generally faster than level 3 by about 30%, therefore we would want to minimize the time |
| * a method spends at level 3. We should only spend the time at level 3 that is necessary to get |
| * adequate profiling. So, if the C2 queue is long enough it is more beneficial to go first to |
| * level 2, because if we transitioned to level 3 we would be stuck there until our C2 compile |
| * request makes its way through the long queue. When the load on C2 recedes we are going to |
| * recompile at level 3 and start gathering profiling information. |
| * 2. The length of C1 queue is used to dynamically adjust the thresholds, so as to introduce |
| * additional filtering if the compiler is overloaded. The rationale is that by the time a |
| * method gets compiled it can become unused, so it doesn't make sense to put too much onto the |
| * queue. |
| * |
| * After profiling is completed at level 3 the transition is made to level 4. Again, the length |
| * of the C2 queue is used as a feedback to adjust the thresholds. |
| * |
| * After the first C1 compile some basic information is determined about the code like the number |
| * of the blocks and the number of the loops. Based on that it can be decided that a method |
| * is trivial and compiling it with C1 will yield the same code. In this case the method is |
| * compiled at level 1 instead of 4. |
| * |
| * We also support profiling at level 0. If C1 is slow enough to produce the level 3 version of |
| * the code and the C2 queue is sufficiently small we can decide to start profiling in the |
| * interpreter (and continue profiling in the compiled code once the level 3 version arrives). |
| * If the profiling at level 0 is fully completed before level 3 version is produced, a level 2 |
| * version is compiled instead in order to run faster waiting for a level 4 version. |
| * |
| * Compile queues are implemented as priority queues - for each method in the queue we compute |
| * the event rate (the number of invocation and backedge counter increments per unit of time). |
| * When getting an element off the queue we pick the one with the largest rate. Maintaining the |
| * rate also allows us to remove stale methods (the ones that got on the queue but stopped |
| * being used shortly after that). |
| */ |
| |
| /* Command line options: |
| * - Tier?InvokeNotifyFreqLog and Tier?BackedgeNotifyFreqLog control the frequency of method |
| * invocation and backedge notifications. Basically every n-th invocation or backedge a mutator thread |
| * makes a call into the runtime. |
| * |
| * - Tier?CompileThreshold, Tier?BackEdgeThreshold, Tier?MinInvocationThreshold control |
| * compilation thresholds. |
| * Level 2 thresholds are not used and are provided for option-compatibility and potential future use. |
| * Other thresholds work as follows: |
| * |
| * Transition from interpreter (level 0) to C1 with full profiling (level 3) happens when |
| * the following predicate is true (X is the level): |
| * |
| * i > TierXInvocationThreshold * s || (i > TierXMinInvocationThreshold * s && i + b > TierXCompileThreshold * s), |
| * |
| * where $i$ is the number of method invocations, $b$ number of backedges and $s$ is the scaling |
| * coefficient that will be discussed further. |
| * The intuition is to equalize the time that is spend profiling each method. |
| * The same predicate is used to control the transition from level 3 to level 4 (C2). It should be |
| * noted though that the thresholds are relative. Moreover i and b for the 0->3 transition come |
| * from Method* and for 3->4 transition they come from MDO (since profiled invocations are |
| * counted separately). |
| * |
| * OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates. |
| * |
| * - Tier?LoadFeedback options are used to automatically scale the predicates described above depending |
| * on the compiler load. The scaling coefficients are computed as follows: |
| * |
| * s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1, |
| * |
| * where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X |
| * is the number of level X compiler threads. |
| * |
| * Basically these parameters describe how many methods should be in the compile queue |
| * per compiler thread before the scaling coefficient increases by one. |
| * |
| * This feedback provides the mechanism to automatically control the flow of compilation requests |
| * depending on the machine speed, mutator load and other external factors. |
| * |
| * - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop. |
| * Consider the following observation: a method compiled with full profiling (level 3) |
| * is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO). |
| * Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue |
| * gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues |
| * executing at level 3 for much longer time than is required by the predicate and at suboptimal speed. |
| * The idea is to dynamically change the behavior of the system in such a way that if a substantial |
| * load on C2 is detected we would first do the 0->2 transition allowing a method to run faster. |
| * And then when the load decreases to allow 2->3 transitions. |
| * |
| * Tier3Delay* parameters control this switching mechanism. |
| * Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy |
| * no longer does 0->3 transitions but does 0->2 transitions instead. |
| * Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue |
| * per compiler thread falls below the specified amount. |
| * The hysteresis is necessary to avoid jitter. |
| * |
| * - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue. |
| * Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to |
| * compile from the compile queue, we also can detect stale methods for which the rate has been |
| * 0 for some time in the same iteration. Stale methods can appear in the queue when an application |
| * abruptly changes its behavior. |
| * |
| * - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick |
| * to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything |
| * with pure c1. |
| * |
| * - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the |
| * 0->3 predicate are already exceeded by the given percentage but the level 3 version of the |
| * method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled |
| * version in time. This reduces the overall transition to level 4 and decreases the startup time. |
| * Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long |
| * these is not reason to start profiling prematurely. |
| * |
| * - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation. |
| * Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered |
| * to be zero if no events occurred in TieredRateUpdateMaxTime. |
| */ |
| |
| |
| class AdvancedThresholdPolicy : public SimpleThresholdPolicy { |
| jlong _start_time; |
| |
| // Call and loop predicates determine whether a transition to a higher compilation |
| // level should be performed (pointers to predicate functions are passed to common(). |
| // Predicates also take compiler load into account. |
| typedef bool (AdvancedThresholdPolicy::*Predicate)(int i, int b, CompLevel cur_level); |
| bool call_predicate(int i, int b, CompLevel cur_level); |
| bool loop_predicate(int i, int b, CompLevel cur_level); |
| // Common transition function. Given a predicate determines if a method should transition to another level. |
| CompLevel common(Predicate p, Method* method, CompLevel cur_level, bool disable_feedback = false); |
| // Transition functions. |
| // call_event determines if a method should be compiled at a different |
| // level with a regular invocation entry. |
| CompLevel call_event(Method* method, CompLevel cur_level); |
| // loop_event checks if a method should be OSR compiled at a different |
| // level. |
| CompLevel loop_event(Method* method, CompLevel cur_level); |
| // Has a method been long around? |
| // We don't remove old methods from the compile queue even if they have |
| // very low activity (see select_task()). |
| inline bool is_old(Method* method); |
| // Was a given method inactive for a given number of milliseconds. |
| // If it is, we would remove it from the queue (see select_task()). |
| inline bool is_stale(jlong t, jlong timeout, Method* m); |
| // Compute the weight of the method for the compilation scheduling |
| inline double weight(Method* method); |
| // Apply heuristics and return true if x should be compiled before y |
| inline bool compare_methods(Method* x, Method* y); |
| // Compute event rate for a given method. The rate is the number of event (invocations + backedges) |
| // per millisecond. |
| inline void update_rate(jlong t, Method* m); |
| // Compute threshold scaling coefficient |
| inline double threshold_scale(CompLevel level, int feedback_k); |
| // If a method is old enough and is still in the interpreter we would want to |
| // start profiling without waiting for the compiled method to arrive. This function |
| // determines whether we should do that. |
| inline bool should_create_mdo(Method* method, CompLevel cur_level); |
| // Create MDO if necessary. |
| void create_mdo(methodHandle mh, JavaThread* thread); |
| // Is method profiled enough? |
| bool is_method_profiled(Method* method); |
| |
| double _increase_threshold_at_ratio; |
| |
| protected: |
| void print_specific(EventType type, methodHandle mh, methodHandle imh, int bci, CompLevel level); |
| |
| void set_increase_threshold_at_ratio() { _increase_threshold_at_ratio = 100 / (100 - (double)IncreaseFirstTierCompileThresholdAt); } |
| void set_start_time(jlong t) { _start_time = t; } |
| jlong start_time() const { return _start_time; } |
| |
| // Submit a given method for compilation (and update the rate). |
| virtual void submit_compile(methodHandle mh, int bci, CompLevel level, JavaThread* thread); |
| // event() from SimpleThresholdPolicy would call these. |
| virtual void method_invocation_event(methodHandle method, methodHandle inlinee, |
| CompLevel level, nmethod* nm, JavaThread* thread); |
| virtual void method_back_branch_event(methodHandle method, methodHandle inlinee, |
| int bci, CompLevel level, nmethod* nm, JavaThread* thread); |
| public: |
| AdvancedThresholdPolicy() : _start_time(0) { } |
| // Select task is called by CompileBroker. We should return a task or NULL. |
| virtual CompileTask* select_task(CompileQueue* compile_queue); |
| virtual void initialize(); |
| virtual bool should_not_inline(ciEnv* env, ciMethod* callee); |
| |
| }; |
| |
| #endif // TIERED |
| |
| #endif // SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP |