--- /dev/null	2011-03-03 14:50:42.000000000 -0800
+++ new/src/share/vm/runtime/advancedThresholdPolicy.hpp	2011-03-03 14:50:42.726666000 -0800
@@ -0,0 +1,207 @@
+/*
+* Copyright (c) 2010, 2011 Oracle and/or its affiliates. All rights reserved.
+* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
+*/
+
+#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);
+  // 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, TRAPS);
+  // 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, TRAPS);
+  // event() from SimpleThresholdPolicy would call these.
+  virtual void method_invocation_event(methodHandle method, methodHandle inlinee,
+                                       CompLevel level, TRAPS);
+  virtual void method_back_branch_event(methodHandle method, methodHandle inlinee,
+                                        int bci, CompLevel level, TRAPS);
+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();
+};
+
+#endif // TIERED
+
+#endif // SHARE_VM_RUNTIME_ADVANCEDTHRESHOLDPOLICY_HPP