--- old/src/share/vm/runtime/advancedThresholdPolicy.hpp
          +++ new/src/share/vm/runtime/advancedThresholdPolicy.hpp

   1    1  /*
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   3    3   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4    4   *
   5    5   * This code is free software; you can redistribute it and/or modify it
   6    6   * under the terms of the GNU General Public License version 2 only, as
   7    7   * published by the Free Software Foundation.
   8    8   *
   9    9   * This code is distributed in the hope that it will be useful, but WITHOUT
  10   10   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11   11   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12   12   * version 2 for more details (a copy is included in the LICENSE file that
  13   13   * accompanied this code).
  14   14   *
  15   15   * You should have received a copy of the GNU General Public License version
  16   16   * 2 along with this work; if not, write to the Free Software Foundation,
  17   17   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18   18   *
  19   19   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20   20   * or visit www.oracle.com if you need additional information or have any
  21   21   * questions.
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  24   24  
  25   25  #ifndef SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP
  26   26  #define SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP
  27   27  
  28   28  #include "runtime/simpleThresholdPolicy.hpp"
  29   29  
  30   30  #ifdef TIERED
  31   31  class CompileTask;
  32   32  class CompileQueue;
  33   33  
  34   34  /*
  35   35   *  The system supports 5 execution levels:
  36   36   *  * level 0 - interpreter
  37   37   *  * level 1 - C1 with full optimization (no profiling)
  38   38   *  * level 2 - C1 with invocation and backedge counters
  39   39   *  * level 3 - C1 with full profiling (level 2 + MDO)
  40   40   *  * level 4 - C2
  41   41   *
  42   42   * Levels 0, 2 and 3 periodically notify the runtime about the current value of the counters
  43   43   * (invocation counters and backedge counters). The frequency of these notifications is
  44   44   * different at each level. These notifications are used by the policy to decide what transition
  45   45   * to make.
  46   46   *
  47   47   * Execution starts at level 0 (interpreter), then the policy can decide either to compile the
  48   48   * method at level 3 or level 2. The decision is based on the following factors:
  49   49   *    1. The length of the C2 queue determines the next level. The observation is that level 2
  50   50   * is generally faster than level 3 by about 30%, therefore we would want to minimize the time
  51   51   * a method spends at level 3. We should only spend the time at level 3 that is necessary to get
  52   52   * adequate profiling. So, if the C2 queue is long enough it is more beneficial to go first to
  53   53   * level 2, because if we transitioned to level 3 we would be stuck there until our C2 compile
  54   54   * request makes its way through the long queue. When the load on C2 recedes we are going to
  55   55   * recompile at level 3 and start gathering profiling information.
  56   56   *    2. The length of C1 queue is used to dynamically adjust the thresholds, so as to introduce
  57   57   * additional filtering if the compiler is overloaded. The rationale is that by the time a
  58   58   * method gets compiled it can become unused, so it doesn't make sense to put too much onto the
  59   59   * queue.
  60   60   *
  61   61   * After profiling is completed at level 3 the transition is made to level 4. Again, the length
  62   62   * of the C2 queue is used as a feedback to adjust the thresholds.
  63   63   *
  64   64   * After the first C1 compile some basic information is determined about the code like the number
  65   65   * of the blocks and the number of the loops. Based on that it can be decided that a method
  66   66   * is trivial and compiling it with C1 will yield the same code. In this case the method is
  67   67   * compiled at level 1 instead of 4.
  68   68   *
  69   69   * We also support profiling at level 0. If C1 is slow enough to produce the level 3 version of
  70   70   * the code and the C2 queue is sufficiently small we can decide to start profiling in the
  71   71   * interpreter (and continue profiling in the compiled code once the level 3 version arrives).
  72   72   * If the profiling at level 0 is fully completed before level 3 version is produced, a level 2
  73   73   * version is compiled instead in order to run faster waiting for a level 4 version.
  74   74   *
  75   75   * Compile queues are implemented as priority queues - for each method in the queue we compute
  76   76   * the event rate (the number of invocation and backedge counter increments per unit of time).
  77   77   * When getting an element off the queue we pick the one with the largest rate. Maintaining the
  78   78   * rate also allows us to remove stale methods (the ones that got on the queue but stopped
  79   79   * being used shortly after that).
  80   80  */
  81   81  
  82   82  /* Command line options:
  83   83   * - Tier?InvokeNotifyFreqLog and Tier?BackedgeNotifyFreqLog control the frequency of method
  84   84   *   invocation and backedge notifications. Basically every n-th invocation or backedge a mutator thread
  85   85   *   makes a call into the runtime.
  86   86   *
  87   87   * - Tier?CompileThreshold, Tier?BackEdgeThreshold, Tier?MinInvocationThreshold control
  88   88   *   compilation thresholds.
  89   89   *   Level 2 thresholds are not used and are provided for option-compatibility and potential future use.
  90   90   *   Other thresholds work as follows:
  91   91   *
  92   92   *   Transition from interpreter (level 0) to C1 with full profiling (level 3) happens when
  93   93   *   the following predicate is true (X is the level):
  94   94   *
  95   95   *   i > TierXInvocationThreshold * s || (i > TierXMinInvocationThreshold * s  && i + b > TierXCompileThreshold * s),
  96   96   *
  97   97   *   where $i$ is the number of method invocations, $b$ number of backedges and $s$ is the scaling
  98   98   *   coefficient that will be discussed further.
  99   99   *   The intuition is to equalize the time that is spend profiling each method.
 100  100   *   The same predicate is used to control the transition from level 3 to level 4 (C2). It should be
 101  101   *   noted though that the thresholds are relative. Moreover i and b for the 0->3 transition come
 102  102   *   from methodOop and for 3->4 transition they come from MDO (since profiled invocations are
 103  103   *   counted separately).
 104  104   *
 105  105   *   OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates.
 106  106   *
 107  107   * - Tier?LoadFeedback options are used to automatically scale the predicates described above depending
 108  108   *   on the compiler load. The scaling coefficients are computed as follows:
 109  109   *
 110  110   *   s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1,
 111  111   *
 112  112   *   where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X
 113  113   *   is the number of level X compiler threads.
 114  114   *
 115  115   *   Basically these parameters describe how many methods should be in the compile queue
 116  116   *   per compiler thread before the scaling coefficient increases by one.
 117  117   *
 118  118   *   This feedback provides the mechanism to automatically control the flow of compilation requests
 119  119   *   depending on the machine speed, mutator load and other external factors.
 120  120   *
 121  121   * - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop.
 122  122   *   Consider the following observation: a method compiled with full profiling (level 3)
 123  123   *   is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO).
 124  124   *   Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue
 125  125   *   gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues
 126  126   *   executing at level 3 for much longer time than is required by the predicate and at suboptimal speed.
 127  127   *   The idea is to dynamically change the behavior of the system in such a way that if a substantial
 128  128   *   load on C2 is detected we would first do the 0->2 transition allowing a method to run faster.
 129  129   *   And then when the load decreases to allow 2->3 transitions.
 130  130   *
 131  131   *   Tier3Delay* parameters control this switching mechanism.
 132  132   *   Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy
 133  133   *   no longer does 0->3 transitions but does 0->2 transitions instead.
 134  134   *   Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue
 135  135   *   per compiler thread falls below the specified amount.
 136  136   *   The hysteresis is necessary to avoid jitter.
 137  137   *
 138  138   * - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue.
 139  139   *   Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to
 140  140   *   compile from the compile queue, we also can detect stale methods for which the rate has been
 141  141   *   0 for some time in the same iteration. Stale methods can appear in the queue when an application
 142  142   *   abruptly changes its behavior.
 143  143   *
 144  144   * - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick
 145  145   *   to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything
 146  146   *   with pure c1.
 147  147   *
 148  148   * - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the
 149  149   *   0->3 predicate are already exceeded by the given percentage but the level 3 version of the
 150  150   *   method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled
 151  151   *   version in time. This reduces the overall transition to level 4 and decreases the startup time.
 152  152   *   Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long
 153  153   *   these is not reason to start profiling prematurely.
 154  154   *
 155  155   * - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation.
 156  156   *   Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered
 157  157   *   to be zero if no events occurred in TieredRateUpdateMaxTime.
 158  158   */
 159  159  
 160  160  

 161  161  class AdvancedThresholdPolicy : public SimpleThresholdPolicy {
 162  162    jlong _start_time;
 163  163  
 164  164    // Call and loop predicates determine whether a transition to a higher compilation
 165  165    // level should be performed (pointers to predicate functions are passed to common().
 166  166    // Predicates also take compiler load into account.
 167  167    typedef bool (AdvancedThresholdPolicy::*Predicate)(int i, int b, CompLevel cur_level);
 168  168    bool call_predicate(int i, int b, CompLevel cur_level);
 169  169    bool loop_predicate(int i, int b, CompLevel cur_level);
 170  170    // Common transition function. Given a predicate determines if a method should transition to another level.
 171      -  CompLevel common(Predicate p, methodOop method, CompLevel cur_level);
      171 +  CompLevel common(Predicate p, methodOop method, CompLevel cur_level, bool disable_feedback = false);
 172  172    // Transition functions.
 173  173    // call_event determines if a method should be compiled at a different
 174  174    // level with a regular invocation entry.
 175  175    CompLevel call_event(methodOop method, CompLevel cur_level);
 176  176    // loop_event checks if a method should be OSR compiled at a different
 177  177    // level.
 178  178    CompLevel loop_event(methodOop method, CompLevel cur_level);
 179  179    // Has a method been long around?
 180  180    // We don't remove old methods from the compile queue even if they have
 181  181    // very low activity (see select_task()).

 182  182    inline bool is_old(methodOop method);
 183  183    // Was a given method inactive for a given number of milliseconds.
 184  184    // If it is, we would remove it from the queue (see select_task()).
 185  185    inline bool is_stale(jlong t, jlong timeout, methodOop m);
 186  186    // Compute the weight of the method for the compilation scheduling
 187  187    inline double weight(methodOop method);
 188  188    // Apply heuristics and return true if x should be compiled before y
 189  189    inline bool compare_methods(methodOop x, methodOop y);
 190  190    // Compute event rate for a given method. The rate is the number of event (invocations + backedges)
 191  191    // per millisecond.
 192  192    inline void update_rate(jlong t, methodOop m);
 193  193    // Compute threshold scaling coefficient
 194  194    inline double threshold_scale(CompLevel level, int feedback_k);
 195  195    // If a method is old enough and is still in the interpreter we would want to
 196  196    // start profiling without waiting for the compiled method to arrive. This function
 197  197    // determines whether we should do that.
 198  198    inline bool should_create_mdo(methodOop method, CompLevel cur_level);
 199  199    // Create MDO if necessary.
 200  200    void create_mdo(methodHandle mh, TRAPS);
 201  201    // Is method profiled enough?
 202  202    bool is_method_profiled(methodOop method);
 203  203  
 204  204  protected:
 205  205    void print_specific(EventType type, methodHandle mh, methodHandle imh, int bci, CompLevel level);
 206  206  
 207  207    void set_start_time(jlong t) { _start_time = t;    }
 208  208    jlong start_time() const     { return _start_time; }
 209  209  
 210  210    // Submit a given method for compilation (and update the rate).
 211  211    virtual void submit_compile(methodHandle mh, int bci, CompLevel level, TRAPS);
 212  212    // event() from SimpleThresholdPolicy would call these.
 213  213    virtual void method_invocation_event(methodHandle method, methodHandle inlinee,
 214  214                                         CompLevel level, nmethod* nm, TRAPS);
 215  215    virtual void method_back_branch_event(methodHandle method, methodHandle inlinee,
 216  216                                          int bci, CompLevel level, nmethod* nm, TRAPS);
 217  217  public:
 218  218    AdvancedThresholdPolicy() : _start_time(0) { }
 219  219    // Select task is called by CompileBroker. We should return a task or NULL.
 220  220    virtual CompileTask* select_task(CompileQueue* compile_queue);
 221  221    virtual void initialize();
 222  222    virtual bool should_not_inline(ciEnv* env, ciMethod* callee);
 223  223  
 224  224  };
 225  225  
 226  226  #endif // TIERED
 227  227  
 228  228  #endif // SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP

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