234 lines
13 KiB
C++
234 lines
13 KiB
C++
/*
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* Copyright (c) 2010, 2015, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#ifndef SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP
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#define SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP
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#include "runtime/simpleThresholdPolicy.hpp"
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#ifdef TIERED
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class CompileTask;
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class CompileQueue;
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/*
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* The system supports 5 execution levels:
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* * level 0 - interpreter
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* * level 1 - C1 with full optimization (no profiling)
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* * level 2 - C1 with invocation and backedge counters
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* * level 3 - C1 with full profiling (level 2 + MDO)
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* * level 4 - C2
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*
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* Levels 0, 2 and 3 periodically notify the runtime about the current value of the counters
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* (invocation counters and backedge counters). The frequency of these notifications is
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* different at each level. These notifications are used by the policy to decide what transition
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* to make.
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*
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* Execution starts at level 0 (interpreter), then the policy can decide either to compile the
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* method at level 3 or level 2. The decision is based on the following factors:
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* 1. The length of the C2 queue determines the next level. The observation is that level 2
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* is generally faster than level 3 by about 30%, therefore we would want to minimize the time
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* a method spends at level 3. We should only spend the time at level 3 that is necessary to get
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* adequate profiling. So, if the C2 queue is long enough it is more beneficial to go first to
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* level 2, because if we transitioned to level 3 we would be stuck there until our C2 compile
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* request makes its way through the long queue. When the load on C2 recedes we are going to
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* recompile at level 3 and start gathering profiling information.
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* 2. The length of C1 queue is used to dynamically adjust the thresholds, so as to introduce
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* additional filtering if the compiler is overloaded. The rationale is that by the time a
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* method gets compiled it can become unused, so it doesn't make sense to put too much onto the
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* queue.
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*
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* After profiling is completed at level 3 the transition is made to level 4. Again, the length
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* of the C2 queue is used as a feedback to adjust the thresholds.
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*
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* After the first C1 compile some basic information is determined about the code like the number
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* of the blocks and the number of the loops. Based on that it can be decided that a method
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* is trivial and compiling it with C1 will yield the same code. In this case the method is
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* compiled at level 1 instead of 4.
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*
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* We also support profiling at level 0. If C1 is slow enough to produce the level 3 version of
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* the code and the C2 queue is sufficiently small we can decide to start profiling in the
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* interpreter (and continue profiling in the compiled code once the level 3 version arrives).
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* If the profiling at level 0 is fully completed before level 3 version is produced, a level 2
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* version is compiled instead in order to run faster waiting for a level 4 version.
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*
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* Compile queues are implemented as priority queues - for each method in the queue we compute
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* the event rate (the number of invocation and backedge counter increments per unit of time).
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* When getting an element off the queue we pick the one with the largest rate. Maintaining the
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* rate also allows us to remove stale methods (the ones that got on the queue but stopped
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* being used shortly after that).
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*/
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/* Command line options:
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* - Tier?InvokeNotifyFreqLog and Tier?BackedgeNotifyFreqLog control the frequency of method
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* invocation and backedge notifications. Basically every n-th invocation or backedge a mutator thread
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* makes a call into the runtime.
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*
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* - Tier?InvocationThreshold, Tier?CompileThreshold, Tier?BackEdgeThreshold, Tier?MinInvocationThreshold control
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* compilation thresholds.
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* Level 2 thresholds are not used and are provided for option-compatibility and potential future use.
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* Other thresholds work as follows:
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*
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* Transition from interpreter (level 0) to C1 with full profiling (level 3) happens when
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* the following predicate is true (X is the level):
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*
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* i > TierXInvocationThreshold * s || (i > TierXMinInvocationThreshold * s && i + b > TierXCompileThreshold * s),
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*
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* where $i$ is the number of method invocations, $b$ number of backedges and $s$ is the scaling
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* coefficient that will be discussed further.
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* The intuition is to equalize the time that is spend profiling each method.
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* The same predicate is used to control the transition from level 3 to level 4 (C2). It should be
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* noted though that the thresholds are relative. Moreover i and b for the 0->3 transition come
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* from Method* and for 3->4 transition they come from MDO (since profiled invocations are
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* counted separately). Finally, if a method does not contain anything worth profiling, a transition
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* from level 3 to level 4 occurs without considering thresholds (e.g., with fewer invocations than
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* what is specified by Tier4InvocationThreshold).
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*
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* OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates.
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*
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* - Tier?LoadFeedback options are used to automatically scale the predicates described above depending
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* on the compiler load. The scaling coefficients are computed as follows:
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*
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* s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1,
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*
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* where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X
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* is the number of level X compiler threads.
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*
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* Basically these parameters describe how many methods should be in the compile queue
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* per compiler thread before the scaling coefficient increases by one.
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*
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* This feedback provides the mechanism to automatically control the flow of compilation requests
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* depending on the machine speed, mutator load and other external factors.
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*
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* - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop.
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* Consider the following observation: a method compiled with full profiling (level 3)
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* is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO).
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* Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue
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* gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues
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* executing at level 3 for much longer time than is required by the predicate and at suboptimal speed.
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* The idea is to dynamically change the behavior of the system in such a way that if a substantial
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* load on C2 is detected we would first do the 0->2 transition allowing a method to run faster.
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* And then when the load decreases to allow 2->3 transitions.
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*
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* Tier3Delay* parameters control this switching mechanism.
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* Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy
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* no longer does 0->3 transitions but does 0->2 transitions instead.
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* Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue
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* per compiler thread falls below the specified amount.
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* The hysteresis is necessary to avoid jitter.
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*
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* - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue.
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* Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to
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* compile from the compile queue, we also can detect stale methods for which the rate has been
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* 0 for some time in the same iteration. Stale methods can appear in the queue when an application
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* abruptly changes its behavior.
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*
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* - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick
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* to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything
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* with pure c1.
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*
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* - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the
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* 0->3 predicate are already exceeded by the given percentage but the level 3 version of the
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* method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled
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* version in time. This reduces the overall transition to level 4 and decreases the startup time.
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* Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long
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* these is not reason to start profiling prematurely.
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*
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* - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation.
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* Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered
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* to be zero if no events occurred in TieredRateUpdateMaxTime.
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*/
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class AdvancedThresholdPolicy : public SimpleThresholdPolicy {
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jlong _start_time;
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// Call and loop predicates determine whether a transition to a higher compilation
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// level should be performed (pointers to predicate functions are passed to common().
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// Predicates also take compiler load into account.
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typedef bool (AdvancedThresholdPolicy::*Predicate)(int i, int b, CompLevel cur_level, Method* method);
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bool call_predicate(int i, int b, CompLevel cur_level, Method* method);
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bool loop_predicate(int i, int b, CompLevel cur_level, Method* method);
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// Common transition function. Given a predicate determines if a method should transition to another level.
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CompLevel common(Predicate p, Method* method, CompLevel cur_level, bool disable_feedback = false);
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// Transition functions.
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// call_event determines if a method should be compiled at a different
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// level with a regular invocation entry.
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CompLevel call_event(Method* method, CompLevel cur_level);
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// loop_event checks if a method should be OSR compiled at a different
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// level.
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CompLevel loop_event(Method* method, CompLevel cur_level);
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// Has a method been long around?
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// We don't remove old methods from the compile queue even if they have
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// very low activity (see select_task()).
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inline bool is_old(Method* method);
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// Was a given method inactive for a given number of milliseconds.
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// If it is, we would remove it from the queue (see select_task()).
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inline bool is_stale(jlong t, jlong timeout, Method* m);
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// Compute the weight of the method for the compilation scheduling
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inline double weight(Method* method);
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// Apply heuristics and return true if x should be compiled before y
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inline bool compare_methods(Method* x, Method* y);
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// Compute event rate for a given method. The rate is the number of event (invocations + backedges)
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// per millisecond.
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inline void update_rate(jlong t, Method* m);
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// Compute threshold scaling coefficient
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inline double threshold_scale(CompLevel level, int feedback_k);
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// If a method is old enough and is still in the interpreter we would want to
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// start profiling without waiting for the compiled method to arrive. This function
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// determines whether we should do that.
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inline bool should_create_mdo(Method* method, CompLevel cur_level);
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// Create MDO if necessary.
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void create_mdo(methodHandle mh, JavaThread* thread);
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// Is method profiled enough?
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bool is_method_profiled(Method* method);
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double _increase_threshold_at_ratio;
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protected:
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void print_specific(EventType type, methodHandle mh, methodHandle imh, int bci, CompLevel level);
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void set_increase_threshold_at_ratio() { _increase_threshold_at_ratio = 100 / (100 - (double)IncreaseFirstTierCompileThresholdAt); }
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void set_start_time(jlong t) { _start_time = t; }
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jlong start_time() const { return _start_time; }
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// Submit a given method for compilation (and update the rate).
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virtual void submit_compile(const methodHandle& mh, int bci, CompLevel level, JavaThread* thread);
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// event() from SimpleThresholdPolicy would call these.
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virtual void method_invocation_event(const methodHandle& method, const methodHandle& inlinee,
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CompLevel level, nmethod* nm, JavaThread* thread);
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virtual void method_back_branch_event(const methodHandle& method, const methodHandle& inlinee,
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int bci, CompLevel level, nmethod* nm, JavaThread* thread);
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public:
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AdvancedThresholdPolicy() : _start_time(0) { }
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// Select task is called by CompileBroker. We should return a task or NULL.
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virtual CompileTask* select_task(CompileQueue* compile_queue);
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virtual void initialize();
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virtual bool should_not_inline(ciEnv* env, ciMethod* callee);
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};
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#endif // TIERED
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#endif // SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP
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