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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 *

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 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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

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

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#ifndef SHARE_VM_RUNTIME_SIMPLETHRESHOLDPOLICY_HPP

#define SHARE_VM_RUNTIME_SIMPLETHRESHOLDPOLICY_HPP

#include "code/nmethod.hpp"

#include "oops/methodData.hpp"

#include "runtime/compilationPolicy.hpp"

#include "utilities/globalDefinitions.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?InvocationThreshold, 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 Method* and for 3->4 transition they come from MDO (since profiled invocations are

 *   counted separately). Finally, if a method does not contain anything worth profiling, a transition

 *   from level 3 to level 4 occurs without considering thresholds (e.g., with fewer invocations than

 *   what is specified by Tier4InvocationThreshold).

 *

 *   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 SimpleThresholdPolicy : public CompilationPolicy {

  jlong _start_time;

  int _c1_count, _c2_count;

  // Check if the counter is big enough and set carry (effectively infinity).

  inline void set_carry_if_necessary(InvocationCounter *counter);

  // Set carry flags in the counters (in Method* and MDO).

  inline void handle_counter_overflow(Method* method);

  // Call and loop predicates determine whether a transition to a higher compilation

  // level should be performed (pointers to predicate functions are passed to common_TF().

  // Predicates also take compiler load into account.

  typedef bool (SimpleThresholdPolicy::*Predicate)(int i, int b, CompLevel cur_level, Method* method);

  bool call_predicate(int i, int b, CompLevel cur_level, Method* method);

  bool loop_predicate(int i, int b, CompLevel cur_level, Method* method);

  // Common transition function. Given a predicate determines if a method should transition to another level.

  CompLevel common(Predicate p, Method* 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(Method* method, CompLevel cur_level, JavaThread* thread);

  // loop_event checks if a method should be OSR compiled at a different

  // level.

  CompLevel loop_event(Method* method, CompLevel cur_level, JavaThread* thread);

  void print_counters(const char* prefix, const methodHandle& mh);

  // 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(Method* 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, Method* m);

  // Compute the weight of the method for the compilation scheduling

  inline double weight(Method* method);

  // Apply heuristics and return true if x should be compiled before y

  inline bool compare_methods(Method* x, Method* 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, Method* 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(Method* method, CompLevel cur_level);

  // Create MDO if necessary.

  void create_mdo(const methodHandle& mh, JavaThread* thread);

  // Is method profiled enough?

  bool is_method_profiled(Method* method);

  double _increase_threshold_at_ratio;

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

protected:

  int c1_count() const     { return _c1_count; }

  int c2_count() const     { return _c2_count; }

  void set_c1_count(int x) { _c1_count = x;    }

  void set_c2_count(int x) { _c2_count = x;    }

  enum EventType { CALL, LOOP, COMPILE, REMOVE_FROM_QUEUE, UPDATE_IN_QUEUE, REPROFILE, MAKE_NOT_ENTRANT };

  void print_event(EventType type, const methodHandle& mh, const methodHandle& imh, int bci, CompLevel level);

  // Print policy-specific information if necessary

  virtual void print_specific(EventType type, const methodHandle& mh, const methodHandle& imh, int bci, CompLevel level);

  // Check if the method can be compiled, change level if necessary

  void compile(const methodHandle& mh, int bci, CompLevel level, JavaThread* thread);

  // Submit a given method for compilation

  virtual void submit_compile(const methodHandle& mh, int bci, CompLevel level, JavaThread* thread);

  // Simple methods are as good being compiled with C1 as C2.

  // This function tells if it's such a function.

  inline bool is_trivial(Method* method);

  // Predicate helpers are used by .*_predicate() methods as well as others.

  // They check the given counter values, multiplied by the scale against the thresholds.

  template<CompLevel level> static inline bool call_predicate_helper(int i, int b, double scale, Method* method);

  template<CompLevel level> static inline bool loop_predicate_helper(int i, int b, double scale, Method* method);

  // Get a compilation level for a given method.

  static CompLevel comp_level(Method* method);

  virtual void method_invocation_event(const methodHandle& method, const methodHandle& inlinee,

                                       CompLevel level, CompiledMethod* nm, JavaThread* thread);

  virtual void method_back_branch_event(const methodHandle& method, const methodHandle& inlinee,

                                        int bci, CompLevel level, CompiledMethod* nm, JavaThread* thread);

  void set_increase_threshold_at_ratio() { _increase_threshold_at_ratio = 100 / (100 - (double)IncreaseFirstTierCompileThresholdAt); }

  void set_start_time(jlong t) { _start_time = t;    }

  jlong start_time() const     { return _start_time; }

public:

  SimpleThresholdPolicy() : _start_time(0), _c1_count(0), _c2_count(0) { }

  virtual int compiler_count(CompLevel comp_level) {

    if (is_c1_compile(comp_level)) return c1_count();

    if (is_c2_compile(comp_level)) return c2_count();

    return 0;

  }

  virtual CompLevel initial_compile_level() { return MIN2((CompLevel)TieredStopAtLevel, CompLevel_initial_compile); }

  virtual void do_safepoint_work() { }

  virtual void delay_compilation(Method* method) { }

  virtual void disable_compilation(Method* method) { }

  virtual void reprofile(ScopeDesc* trap_scope, bool is_osr);

  virtual nmethod* event(const methodHandle& method, const methodHandle& inlinee,

                         int branch_bci, int bci, CompLevel comp_level, CompiledMethod* nm, JavaThread* thread);

  // Select task is called by CompileBroker. We should return a task or NULL.

  virtual CompileTask* select_task(CompileQueue* compile_queue);

  // Tell the runtime if we think a given method is adequately profiled.

  virtual bool is_mature(Method* method);

  // Initialize: set compiler thread count

  virtual void initialize();

  virtual bool should_not_inline(ciEnv* env, ciMethod* callee);

};

#endif // TIERED

#endif // SHARE_VM_RUNTIME_SIMPLETHRESHOLDPOLICY_HPP