1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHAGECENSUS_HPP
26 #define SHARE_GC_SHENANDOAH_SHENANDOAHAGECENSUS_HPP
27
28 #include "gc/shared/ageTable.hpp"
29
30 #ifndef PRODUCT
31 // Enable noise instrumentation
32 #define SHENANDOAH_CENSUS_NOISE 1
33 #endif // PRODUCT
34
35 #ifdef SHENANDOAH_CENSUS_NOISE
36
37 #define CENSUS_NOISE(x) x
38 #define NO_CENSUS_NOISE(x)
39
40 struct ShenandoahNoiseStats {
41 size_t skipped; // Volume of objects skipped
42 size_t aged; // Volume of objects from aged regions
43 size_t clamped; // Volume of objects whose ages were clamped
44 size_t young; // Volume of (rejuvenated) objects of retrograde age
45
46 ShenandoahNoiseStats() {
47 clear();
48 }
49
50 void clear() {
51 skipped = 0;
52 aged = 0;
53 clamped = 0;
54 young = 0;
55 }
56
57 #ifndef PRODUCT
58 bool is_clear() {
59 return (skipped + aged + clamped + young) == 0;
60 }
61 #endif // !PRODUCT
62
63 void merge(ShenandoahNoiseStats& other) {
64 skipped += other.skipped;
65 aged += other.aged;
66 clamped += other.clamped;
67 young += other.young;
68 }
69
70 void print(size_t total);
71 };
72 #else // SHENANDOAH_CENSUS_NOISE
73 #define CENSUS_NOISE(x)
74 #define NO_CENSUS_NOISE(x) x
75 #endif // SHENANDOAH_CENSUS_NOISE
76
77 // A class for tracking a sequence of cohort population vectors (or,
78 // interchangeably, age tables) for up to C=MAX_COHORTS age cohorts, where a cohort
79 // represents the set of objects allocated during a specific inter-GC epoch.
80 // Epochs are demarcated by GC cycles, with those surviving a cycle aging by
81 // an epoch. The census tracks the historical variation of cohort demographics
82 // across N=MAX_SNAPSHOTS recent epochs. Since there are at most C age cohorts in
83 // the population, we need only track at most N=C epochal snapshots to track a
84 // maximal longitudinal demographics of every object's longitudinal cohort in
85 // the young generation. The _global_age_table is thus, currently, a C x N (row-major)
86 // matrix, with C=16, and, for now N=C=16, currently.
87 // In theory, we might decide to track even longer (N=MAX_SNAPSHOTS) demographic
88 // histories, but that isn't the case today. In particular, the current tenuring
89 // threshold algorithm uses only 2 most recent snapshots, with the remaining
90 // MAX_SNAPSHOTS-2=14 reserved for research purposes.
91 //
92 // In addition, this class also maintains per worker population vectors into which
93 // census for the current minor GC is accumulated (during marking or, optionally, during
94 // evacuation). These are cleared after each marking (resectively, evacuation) cycle,
95 // once the per-worker data is consolidated into the appropriate population vector
96 // per minor collection. The _local_age_table is thus C x N, for N GC workers.
97 class ShenandoahAgeCensus: public CHeapObj<mtGC> {
98 AgeTable** _global_age_table; // Global age table used for adapting tenuring threshold, one per snapshot
99 AgeTable** _local_age_table; // Local scratch age tables to track object ages, one per worker
100
101 #ifdef SHENANDOAH_CENSUS_NOISE
102 ShenandoahNoiseStats* _global_noise; // Noise stats, one per snapshot
103 ShenandoahNoiseStats* _local_noise; // Local scratch table for noise stats, one per worker
104 #endif // SHENANDOAH_CENSUS_NOISE
105
106 uint _epoch; // Current epoch (modulo max age)
107 uint *_tenuring_threshold; // An array of the last N tenuring threshold values we
108 // computed.
109
110 // A private work method invoked by the public compute_tenuring_threshold() method.
111 // This uses the data in the ShenandoahAgeCensus object's _global_age_table and the
112 // current _epoch to compute a new tenuring threshold, which will be remembered
113 // until the next invocation of compute_tenuring_threshold.
114 uint compute_tenuring_threshold_work();
115
116 // Mortality rate of a cohort, given its population in
117 // previous and current epochs
118 double mortality_rate(size_t prev_pop, size_t cur_pop);
119
120 // Update the tenuring threshold, calling
121 // compute_tenuring_threshold to calculate the new
122 // value
123 void update_tenuring_threshold();
124 uint compute_tenuring_threshold();
125
126 public:
127 enum {
128 MAX_COHORTS = AgeTable::table_size, // = markWord::max_age + 1
129 MAX_SNAPSHOTS = MAX_COHORTS // May change in the future
130 };
131
132 ShenandoahAgeCensus();
133
134 // Return the local age table (population vector) for worker_id.
135 // Only used in the case of (ShenandoahGenerationalAdaptiveTenuring && !ShenandoahGenerationalCensusAtEvac)
136 AgeTable* get_local_age_table(uint worker_id) {
137 return (AgeTable*) _local_age_table[worker_id];
138 }
139
140 // Update the local age table for worker_id by size for
141 // given obj_age, region_age, and region_youth
142 CENSUS_NOISE(void add(uint obj_age, uint region_age, uint region_youth, size_t size, uint worker_id);)
143 NO_CENSUS_NOISE(void add(uint obj_age, uint region_age, size_t size, uint worker_id);)
144
145 #ifdef SHENANDOAH_CENSUS_NOISE
146 // Update the local skip table for worker_id by size
147 void add_skipped(size_t size, uint worker_id);
148 // Update the local aged region volume table for worker_id by size
149 void add_aged(size_t size, uint worker_id);
150 // Update the local clamped object volume table for worker_id by size
151 void add_clamped(size_t size, uint worker_id);
152 // Update the local (rejuvenated) object volume (retrograde age) for worker_id by size
153 void add_young(size_t size, uint worker_id);
154 #endif // SHENANDOAH_CENSUS_NOISE
155
156 // Update to a new epoch, creating a slot for new census.
157 void prepare_for_census_update();
158
159 // Update the census data, and compute the new tenuring threshold.
160 // age0_pop is the population of Cohort 0 that may have been missed in
161 // the regular census.
162 void update_census(size_t age0_pop, AgeTable* pv1 = nullptr, AgeTable* pv2 = nullptr);
163
164 // Return the most recently computed tenuring threshold
165 uint tenuring_threshold() const { return _tenuring_threshold[_epoch]; }
166
167 // Return the tenuring threshold computed for the previous epoch
168 uint previous_tenuring_threshold() const {
169 assert(_epoch < MAX_SNAPSHOTS, "Error");
170 uint prev = _epoch - 1;
171 if (prev >= MAX_SNAPSHOTS) {
172 // _epoch is 0
173 prev = MAX_SNAPSHOTS - 1;
174 }
175 return _tenuring_threshold[prev];
176 }
177
178 // Reset the epoch, clearing accumulated census history
179 void reset_global();
180 // Reset any partial census information
181 void reset_local();
182
183 // Check whether census information is clear
184 bool is_clear_global();
185 bool is_clear_local();
186
187 // Print the age census information
188 void print();
189 };
190
191 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHAGECENSUS_HPP