1 /*

     2  * Copyright (c) 2010, 2017, 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  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    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(const 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(const methodHandle& mh, CompLevel cur_level, CompLevel next_level, JavaThread* thread);

   209 

   210 protected:

   211   void print_specific(EventType type, const methodHandle& mh, const 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