1 /*
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 12  * version 2 for more details (a copy is included in the LICENSE file that
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 24 
 25 #ifndef SHARE_COMPILER_COMPILATIONPOLICY_HPP
 26 #define SHARE_COMPILER_COMPILATIONPOLICY_HPP
 27 
 28 #include "code/nmethod.hpp"
 29 #include "compiler/compileBroker.hpp"
 30 #include "oops/methodData.hpp"
 31 #include "utilities/globalDefinitions.hpp"
 32 
 33 class CompileTask;
 34 class CompileQueue;
 35 /*
 36  *  The system supports 5 execution levels:
 37  *  * level 0 - interpreter (Profiling is tracked by a MethodData object, or MDO in short)
 38  *  * level 1 - C1 with full optimization (no profiling)
 39  *  * level 2 - C1 with invocation and backedge counters
 40  *  * level 3 - C1 with full profiling (level 2 + All other MDO profiling information)
 41  *  * level 4 - C2 with full profile guided optimization
 42  *
 43  * The MethodData object is created by both the interpreter or either compiler to store any
 44  * profiling information collected on a method (ciMethod::ensure_method_data() for C1 and C2
 45  * and CompilationPolicy::create_mdo() for the interpreter). Both the interpreter and code
 46  * compiled by C1 at level 3 will constantly update profiling information in the MDO during
 47  * execution. The information in the MDO is then used by C1 and C2 during compilation, via
 48  * the compiler interface (ciMethodXXX).
 49  * See ciMethod.cpp and ciMethodData.cpp for information transfer from an MDO to the compilers
 50  * through the compiler interface.
 51  *
 52  * Levels 0, 2 and 3 periodically notify the runtime about the current value of the counters
 53  * (invocation counters and backedge counters). The frequency of these notifications is
 54  * different at each level. These notifications are used by the policy to decide what transition
 55  * to make.
 56  *
 57  * Execution starts at level 0 (interpreter), then the policy can decide either to compile the
 58  * method at level 3 or level 2. The decision is based on the following factors:
 59  *    1. The length of the C2 queue determines the next level. The observation is that level 2
 60  * is generally faster than level 3 by about 30%, therefore we would want to minimize the time
 61  * a method spends at level 3. We should only spend the time at level 3 that is necessary to get
 62  * adequate profiling. So, if the C2 queue is long enough it is more beneficial to go first to
 63  * level 2, because if we transitioned to level 3 we would be stuck there until our C2 compile
 64  * request makes its way through the long queue. When the load on C2 recedes we are going to
 65  * recompile at level 3 and start gathering profiling information.
 66  *    2. The length of C1 queue is used to dynamically adjust the thresholds, so as to introduce
 67  * additional filtering if the compiler is overloaded. The rationale is that by the time a
 68  * method gets compiled it can become unused, so it doesn't make sense to put too much onto the
 69  * queue.
 70  *
 71  * After profiling is completed at level 3 the transition is made to level 4. Again, the length
 72  * of the C2 queue is used as a feedback to adjust the thresholds.
 73  *
 74  * After the first C1 compile some basic information is determined about the code like the number
 75  * of the blocks and the number of the loops. Based on that it can be decided that a method
 76  * is trivial and compiling it with C1 will yield the same code. In this case the method is
 77  * compiled at level 1 instead of 4.
 78  *
 79  * We also support profiling at level 0. If C1 is slow enough to produce the level 3 version of
 80  * the code and the C2 queue is sufficiently small we can decide to start profiling in the
 81  * interpreter (and continue profiling in the compiled code once the level 3 version arrives).
 82  * If the profiling at level 0 is fully completed before level 3 version is produced, a level 2
 83  * version is compiled instead in order to run faster waiting for a level 4 version.
 84  *
 85  * Compile queues are implemented as priority queues - for each method in the queue we compute
 86  * the event rate (the number of invocation and backedge counter increments per unit of time).
 87  * When getting an element off the queue we pick the one with the largest rate. Maintaining the
 88  * rate also allows us to remove stale methods (the ones that got on the queue but stopped
 89  * being used shortly after that).
 90 */
 91 
 92 /* Command line options:
 93  * - Tier?InvokeNotifyFreqLog and Tier?BackedgeNotifyFreqLog control the frequency of method
 94  *   invocation and backedge notifications. Basically every n-th invocation or backedge a mutator thread
 95  *   makes a call into the runtime.
 96  *
 97  * - Tier?InvocationThreshold, Tier?CompileThreshold, Tier?BackEdgeThreshold, Tier?MinInvocationThreshold control
 98  *   compilation thresholds.
 99  *   Level 2 thresholds are not used and are provided for option-compatibility and potential future use.
100  *   Other thresholds work as follows:
101  *
102  *   Transition from interpreter (level 0) to C1 with full profiling (level 3) happens when
103  *   the following predicate is true (X is the level):
104  *
105  *   i > TierXInvocationThreshold * s || (i > TierXMinInvocationThreshold * s  && i + b > TierXCompileThreshold * s),
106  *
107  *   where $i$ is the number of method invocations, $b$ number of backedges and $s$ is the scaling
108  *   coefficient that will be discussed further.
109  *   The intuition is to equalize the time that is spend profiling each method.
110  *   The same predicate is used to control the transition from level 3 to level 4 (C2). It should be
111  *   noted though that the thresholds are relative. Moreover i and b for the 0->3 transition come
112  *   from Method* and for 3->4 transition they come from MDO (since profiled invocations are
113  *   counted separately). Finally, if a method does not contain anything worth profiling, a transition
114  *   from level 3 to level 4 occurs without considering thresholds (e.g., with fewer invocations than
115  *   what is specified by Tier4InvocationThreshold).
116  *
117  *   OSR transitions are controlled simply with b > TierXBackEdgeThreshold * s predicates.
118  *
119  * - Tier?LoadFeedback options are used to automatically scale the predicates described above depending
120  *   on the compiler load. The scaling coefficients are computed as follows:
121  *
122  *   s = queue_size_X / (TierXLoadFeedback * compiler_count_X) + 1,
123  *
124  *   where queue_size_X is the current size of the compiler queue of level X, and compiler_count_X
125  *   is the number of level X compiler threads.
126  *
127  *   Basically these parameters describe how many methods should be in the compile queue
128  *   per compiler thread before the scaling coefficient increases by one.
129  *
130  *   This feedback provides the mechanism to automatically control the flow of compilation requests
131  *   depending on the machine speed, mutator load and other external factors.
132  *
133  * - Tier3DelayOn and Tier3DelayOff parameters control another important feedback loop.
134  *   Consider the following observation: a method compiled with full profiling (level 3)
135  *   is about 30% slower than a method at level 2 (just invocation and backedge counters, no MDO).
136  *   Normally, the following transitions will occur: 0->3->4. The problem arises when the C2 queue
137  *   gets congested and the 3->4 transition is delayed. While the method is the C2 queue it continues
138  *   executing at level 3 for much longer time than is required by the predicate and at suboptimal speed.
139  *   The idea is to dynamically change the behavior of the system in such a way that if a substantial
140  *   load on C2 is detected we would first do the 0->2 transition allowing a method to run faster.
141  *   And then when the load decreases to allow 2->3 transitions.
142  *
143  *   Tier3Delay* parameters control this switching mechanism.
144  *   Tier3DelayOn is the number of methods in the C2 queue per compiler thread after which the policy
145  *   no longer does 0->3 transitions but does 0->2 transitions instead.
146  *   Tier3DelayOff switches the original behavior back when the number of methods in the C2 queue
147  *   per compiler thread falls below the specified amount.
148  *   The hysteresis is necessary to avoid jitter.
149  *
150  * - TieredCompileTaskTimeout is the amount of time an idle method can spend in the compile queue.
151  *   Basically, since we use the event rate d(i + b)/dt as a value of priority when selecting a method to
152  *   compile from the compile queue, we also can detect stale methods for which the rate has been
153  *   0 for some time in the same iteration. Stale methods can appear in the queue when an application
154  *   abruptly changes its behavior.
155  *
156  * - TieredStopAtLevel, is used mostly for testing. It allows to bypass the policy logic and stick
157  *   to a given level. For example it's useful to set TieredStopAtLevel = 1 in order to compile everything
158  *   with pure c1.
159  *
160  * - Tier0ProfilingStartPercentage allows the interpreter to start profiling when the inequalities in the
161  *   0->3 predicate are already exceeded by the given percentage but the level 3 version of the
162  *   method is still not ready. We can even go directly from level 0 to 4 if c1 doesn't produce a compiled
163  *   version in time. This reduces the overall transition to level 4 and decreases the startup time.
164  *   Note that this behavior is also guarded by the Tier3Delay mechanism: when the c2 queue is too long
165  *   these is not reason to start profiling prematurely.
166  *
167  * - TieredRateUpdateMinTime and TieredRateUpdateMaxTime are parameters of the rate computation.
168  *   Basically, the rate is not computed more frequently than TieredRateUpdateMinTime and is considered
169  *   to be zero if no events occurred in TieredRateUpdateMaxTime.
170  */
171 
172 class CompilationPolicy : AllStatic {
173   friend class CallPredicate;
174   friend class LoopPredicate;
175 
176   static jlong _start_time;
177   static int _c1_count, _c2_count;
178   static double _increase_threshold_at_ratio;
179 
180   // Set carry flags in the counters (in Method* and MDO).
181   inline static void handle_counter_overflow(const methodHandle& method);
182   // Verify that a level is consistent with the compilation mode
183   static bool verify_level(CompLevel level);
184   // Clamp the request level according to various constraints.
185   inline static CompLevel limit_level(CompLevel level);
186   // Common transition function. Given a predicate determines if a method should transition to another level.
187   template<typename Predicate>
188   static CompLevel common(const methodHandle& method, CompLevel cur_level, bool disable_feedback = false);
189   // Transition functions.
190   // call_event determines if a method should be compiled at a different
191   // level with a regular invocation entry.
192   static CompLevel call_event(const methodHandle& method, CompLevel cur_level, Thread* thread);
193   // loop_event checks if a method should be OSR compiled at a different
194   // level.
195   static CompLevel loop_event(const methodHandle& method, CompLevel cur_level, Thread* thread);
196   static void print_counters(const char* prefix, const Method* m);
197   // Has a method been long around?
198   // We don't remove old methods from the compile queue even if they have
199   // very low activity (see select_task()).
200   inline static bool is_old(const methodHandle& method);
201   // Was a given method inactive for a given number of milliseconds.
202   // If it is, we would remove it from the queue (see select_task()).
203   inline static bool is_stale(jlong t, jlong timeout, const methodHandle& method);
204   // Compute the weight of the method for the compilation scheduling
205   inline static double weight(Method* method);
206   // Apply heuristics and return true if x should be compiled before y
207   inline static bool compare_methods(Method* x, Method* y);
208   // Compute event rate for a given method. The rate is the number of event (invocations + backedges)
209   // per millisecond.
210   inline static void update_rate(jlong t, const methodHandle& method);
211   // Compute threshold scaling coefficient
212   inline static double threshold_scale(CompLevel level, int feedback_k);
213   // If a method is old enough and is still in the interpreter we would want to
214   // start profiling without waiting for the compiled method to arrive. This function
215   // determines whether we should do that.
216   inline static bool should_create_mdo(const methodHandle& method, CompLevel cur_level);
217   // Create MDO if necessary.
218   static void create_mdo(const methodHandle& mh, JavaThread* THREAD);
219   // Is method profiled enough?
220   static bool is_method_profiled(const methodHandle& method);
221 
222   static void set_c1_count(int x) { _c1_count = x;    }
223   static void set_c2_count(int x) { _c2_count = x;    }
224 
225   enum EventType { CALL, LOOP, COMPILE, REMOVE_FROM_QUEUE, UPDATE_IN_QUEUE, REPROFILE, MAKE_NOT_ENTRANT };
226   static void print_event(EventType type, const Method* m, const Method* im, int bci, CompLevel level);
227   // Check if the method can be compiled, change level if necessary
228   static void compile(const methodHandle& mh, int bci, CompLevel level, TRAPS);
229   // Simple methods are as good being compiled with C1 as C2.
230   // This function tells if it's such a function.
231   inline static bool is_trivial(const methodHandle& method);
232   // Force method to be compiled at CompLevel_simple?
233   inline static bool force_comp_at_level_simple(const methodHandle& method);
234 
235   // Get a compilation level for a given method.
236   static CompLevel comp_level(Method* method);
237   static void method_invocation_event(const methodHandle& method, const methodHandle& inlinee,
238                                CompLevel level, CompiledMethod* nm, TRAPS);
239   static void method_back_branch_event(const methodHandle& method, const methodHandle& inlinee,
240                                 int bci, CompLevel level, CompiledMethod* nm, TRAPS);
241 
242   static void set_increase_threshold_at_ratio() { _increase_threshold_at_ratio = 100 / (100 - (double)IncreaseFirstTierCompileThresholdAt); }
243   static void set_start_time(jlong t) { _start_time = t;    }
244   static jlong start_time()           { return _start_time; }
245 
246   // m must be compiled before executing it
247   static bool must_be_compiled(const methodHandle& m, int comp_level = CompLevel_any);
248 public:
249   static int min_invocations() { return Tier4MinInvocationThreshold; }
250   static int c1_count() { return _c1_count; }
251   static int c2_count() { return _c2_count; }
252   static int compiler_count(CompLevel comp_level);
253 
254   // If m must_be_compiled then request a compilation from the CompileBroker.
255   // This supports the -Xcomp option.
256   static void compile_if_required(const methodHandle& m, TRAPS);
257 
258   // m is allowed to be compiled
259   static bool can_be_compiled(const methodHandle& m, int comp_level = CompLevel_any);
260   // m is allowed to be osr compiled
261   static bool can_be_osr_compiled(const methodHandle& m, int comp_level = CompLevel_any);
262   static bool is_compilation_enabled();
263 
264   static CompileTask* select_task_helper(CompileQueue* compile_queue);
265   // Return initial compile level to use with Xcomp (depends on compilation mode).
266   static void reprofile(ScopeDesc* trap_scope, bool is_osr);
267   static nmethod* event(const methodHandle& method, const methodHandle& inlinee,
268                  int branch_bci, int bci, CompLevel comp_level, CompiledMethod* nm, TRAPS);
269   // Select task is called by CompileBroker. We should return a task or nullptr.
270   static CompileTask* select_task(CompileQueue* compile_queue);
271   // Tell the runtime if we think a given method is adequately profiled.
272   static bool is_mature(Method* method);
273   // Initialize: set compiler thread count
274   static void initialize();
275   static bool should_not_inline(ciEnv* env, ciMethod* callee);
276 
277   // Return desired initial compilation level for Xcomp
278   static CompLevel initial_compile_level(const methodHandle& method);
279   // Return highest level possible
280   static CompLevel highest_compile_level();
281 };
282 
283 #endif // SHARE_COMPILER_COMPILATIONPOLICY_HPP