Mercurial > hg > truffle
view src/share/vm/runtime/advancedThresholdPolicy.hpp @ 4974:ab906cea36f7
First round of minimizing diff vs OpenJDK.
author | Thomas Wuerthinger <thomas.wuerthinger@oracle.com> |
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date | Mon, 27 Feb 2012 15:15:59 +0100 |
parents | 20334ed5ed3c |
children | da91efe96a93 |
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/* * Copyright (c) 2010, 2011, 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 * questions. * */ #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 methodOop 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, methodOop 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(methodOop method, CompLevel cur_level); // loop_event checks if a method should be OSR compiled at a different // level. CompLevel loop_event(methodOop 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(methodOop 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, methodOop m); // Compute the weight of the method for the compilation scheduling inline double weight(methodOop method); // Apply heuristics and return true if x should be compiled before y inline bool compare_methods(methodOop x, methodOop 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, methodOop 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(methodOop method, CompLevel cur_level); // Create MDO if necessary. void create_mdo(methodHandle mh, JavaThread* thread); // Is method profiled enough? bool is_method_profiled(methodOop method); protected: void print_specific(EventType type, methodHandle mh, methodHandle imh, int bci, CompLevel level); 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