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8251462: Simplify compilation policy

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Reviewed-by: cjplummer, kvn
This commit is contained in:
Igor Veresov 2021-01-28 20:51:12 +00:00
parent 71128cf4ce
commit 1519632597
98 changed files with 2343 additions and 3818 deletions
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281
src/hotspot/share/compiler/compilationPolicy.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2010, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -27,23 +27,222 @@
#include "code/nmethod.hpp"
#include "compiler/compileBroker.hpp"
#include "memory/allocation.hpp"
#include "runtime/vmOperations.hpp"
#include "utilities/growableArray.hpp"
#include "oops/methodData.hpp"
#include "utilities/globalDefinitions.hpp"
// The CompilationPolicy selects which method (if any) should be compiled.
// It also decides which methods must always be compiled (i.e., are never
// interpreted).
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).
*/
class CompilationPolicy : public CHeapObj<mtCompiler> {
static CompilationPolicy* _policy;
/* 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 CompilationPolicy : AllStatic {
friend class CallPredicate;
friend class LoopPredicate;
static jlong _start_time;
static int _c1_count, _c2_count;
static double _increase_threshold_at_ratio;
// Set carry flags in the counters (in Method* and MDO).
inline static void handle_counter_overflow(Method* method);
// Verify that a level is consistent with the compilation mode
static bool verify_level(CompLevel level);
// Clamp the request level according to various constraints.
inline static CompLevel limit_level(CompLevel level);
// Common transition function. Given a predicate determines if a method should transition to another level.
template<typename Predicate>
static CompLevel common(const methodHandle& 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.
static CompLevel call_event(const methodHandle& method, CompLevel cur_level, Thread* thread);
// loop_event checks if a method should be OSR compiled at a different
// level.
static CompLevel loop_event(const methodHandle& method, CompLevel cur_level, Thread* thread);
static void print_counters(const char* prefix, Method* m);
// 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 static 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 static bool is_stale(jlong t, jlong timeout, Method* m);
// Compute the weight of the method for the compilation scheduling
inline static double weight(Method* method);
// Apply heuristics and return true if x should be compiled before y
inline static 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 static void update_rate(jlong t, Method* m);
// Compute threshold scaling coefficient
inline static 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 static bool should_create_mdo(const methodHandle& method, CompLevel cur_level);
// Create MDO if necessary.
static void create_mdo(const methodHandle& mh, Thread* thread);
// Is method profiled enough?
static bool is_method_profiled(const methodHandle& method);
static bool maybe_switch_to_aot(const methodHandle& mh, CompLevel cur_level, CompLevel next_level, Thread* thread);
static void set_c1_count(int x) { _c1_count = x; }
static void set_c2_count(int x) { _c2_count = x; }
enum EventType { CALL, LOOP, COMPILE, REMOVE_FROM_QUEUE, UPDATE_IN_QUEUE, REPROFILE, MAKE_NOT_ENTRANT };
static void print_event(EventType type, Method* m, Method* im, int bci, CompLevel level);
// Check if the method can be compiled, change level if necessary
static void compile(const methodHandle& mh, int bci, CompLevel level, TRAPS);
// Simple methods are as good being compiled with C1 as C2.
// This function tells if it's such a function.
inline static bool is_trivial(Method* method);
// Force method to be compiled at CompLevel_simple?
inline static bool force_comp_at_level_simple(const methodHandle& method);
// Get a compilation level for a given method.
static CompLevel comp_level(Method* method);
static void method_invocation_event(const methodHandle& method, const methodHandle& inlinee,
CompLevel level, CompiledMethod* nm, TRAPS);
static void method_back_branch_event(const methodHandle& method, const methodHandle& inlinee,
int bci, CompLevel level, CompiledMethod* nm, TRAPS);
static void set_increase_threshold_at_ratio() { _increase_threshold_at_ratio = 100 / (100 - (double)IncreaseFirstTierCompileThresholdAt); }
static void set_start_time(jlong t) { _start_time = t; }
static jlong start_time() { return _start_time; }
// m must be compiled before executing it
static bool must_be_compiled(const methodHandle& m, int comp_level = CompLevel_all);
public:
static int c1_count() { return _c1_count; }
static int c2_count() { return _c2_count; }
static int compiler_count(CompLevel comp_level);
// If m must_be_compiled then request a compilation from the CompileBroker.
// This supports the -Xcomp option.
static void compile_if_required(const methodHandle& m, TRAPS);
@ -53,57 +252,25 @@ public:
// m is allowed to be osr compiled
static bool can_be_osr_compiled(const methodHandle& m, int comp_level = CompLevel_all);
static bool is_compilation_enabled();
static void set_policy(CompilationPolicy* policy) { _policy = policy; }
static CompilationPolicy* policy() { return _policy; }
static void do_safepoint_work() { }
static CompileTask* select_task_helper(CompileQueue* compile_queue);
// Return initial compile level that is used with Xcomp
virtual CompLevel initial_compile_level(const methodHandle& method) = 0;
virtual int compiler_count(CompLevel comp_level) = 0;
// main notification entry, return a pointer to an nmethod if the OSR is required,
// returns NULL otherwise.
virtual nmethod* event(const methodHandle& method, const methodHandle& inlinee, int branch_bci, int bci, CompLevel comp_level, CompiledMethod* nm, TRAPS) = 0;
// safepoint() is called at the end of the safepoint
virtual void do_safepoint_work() = 0;
// reprofile request
virtual void reprofile(ScopeDesc* trap_scope, bool is_osr) = 0;
// delay_compilation(method) can be called by any component of the runtime to notify the policy
// that it's recommended to delay the compilation of this method.
virtual void delay_compilation(Method* method) = 0;
// Select task is called by CompileBroker. The queue is guaranteed to have at least one
// element and is locked. The function should select one and return it.
virtual CompileTask* select_task(CompileQueue* compile_queue) = 0;
// Return initial compile level to use with Xcomp (depends on compilation mode).
static void reprofile(ScopeDesc* trap_scope, bool is_osr);
static nmethod* event(const methodHandle& method, const methodHandle& inlinee,
int branch_bci, int bci, CompLevel comp_level, CompiledMethod* nm, TRAPS);
// Select task is called by CompileBroker. We should return a task or NULL.
static CompileTask* select_task(CompileQueue* compile_queue);
// Tell the runtime if we think a given method is adequately profiled.
virtual bool is_mature(Method* method) = 0;
// Do policy initialization
virtual void initialize() = 0;
virtual bool should_not_inline(ciEnv* env, ciMethod* method) { return false; }
};
static bool is_mature(Method* method);
// Initialize: set compiler thread count
static void initialize();
static bool should_not_inline(ciEnv* env, ciMethod* callee);
// A simple compilation policy.
class SimpleCompPolicy : public CompilationPolicy {
int _compiler_count;
private:
static void trace_frequency_counter_overflow(const methodHandle& m, int branch_bci, int bci);
static void trace_osr_request(const methodHandle& method, nmethod* osr, int bci);
static void trace_osr_completion(nmethod* osr_nm);
void reset_counter_for_invocation_event(const methodHandle& method);
void reset_counter_for_back_branch_event(const methodHandle& method);
void method_invocation_event(const methodHandle& m, TRAPS);
void method_back_branch_event(const methodHandle& m, int bci, TRAPS);
public:
SimpleCompPolicy() : _compiler_count(0) { }
virtual CompLevel initial_compile_level(const methodHandle& m) { return CompLevel_highest_tier; }
virtual int compiler_count(CompLevel comp_level);
virtual void do_safepoint_work();
virtual void reprofile(ScopeDesc* trap_scope, bool is_osr);
virtual void delay_compilation(Method* method);
virtual bool is_mature(Method* method);
virtual void initialize();
virtual CompileTask* select_task(CompileQueue* compile_queue);
virtual nmethod* event(const methodHandle& method, const methodHandle& inlinee, int branch_bci, int bci, CompLevel comp_level, CompiledMethod* nm, TRAPS);
// Return desired initial compilation level for Xcomp
static CompLevel initial_compile_level(const methodHandle& method);
// Return highest level possible
static CompLevel highest_compile_level();
};
#endif // SHARE_COMPILER_COMPILATIONPOLICY_HPP