1 /*
2 * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26
27 #include "gc/shenandoah/shenandoahFreeSet.hpp"
28 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
29 #include "gc/shenandoah/shenandoahPacer.hpp"
30 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
31 #include "runtime/atomic.hpp"
32 #include "runtime/javaThread.inline.hpp"
33 #include "runtime/mutexLocker.hpp"
34 #include "runtime/threadSMR.hpp"
35
36 /*
37 * In normal concurrent cycle, we have to pace the application to let GC finish.
38 *
39 * Here, we do not know how large would be the collection set, and what are the
40 * relative performances of the each stage in the concurrent cycle, and so we have to
41 * make some assumptions.
42 *
43 * For concurrent mark, there is no clear notion of progress. The moderately accurate
44 * and easy to get metric is the amount of live objects the mark had encountered. But,
45 * that does directly correlate with the used heap, because the heap might be fully
46 * dead or fully alive. We cannot assume either of the extremes: we would either allow
47 * application to run out of memory if we assume heap is fully dead but it is not, and,
48 * conversely, we would pacify application excessively if we assume heap is fully alive
49 * but it is not. So we need to guesstimate the particular expected value for heap liveness.
50 * The best way to do this is apparently recording the past history.
51 *
52 * For concurrent evac and update-refs, we are walking the heap per-region, and so the
53 * notion of progress is clear: we get reported the "used" size from the processed regions
54 * and use the global heap-used as the baseline.
55 *
56 * The allocatable space when GC is running is "free" at the start of phase, but the
57 * accounted budget is based on "used". So, we need to adjust the tax knowing that.
58 */
59
60 void ShenandoahPacer::setup_for_mark() {
61 assert(ShenandoahPacing, "Only be here when pacing is enabled");
62
63 size_t live = update_and_get_progress_history();
64 size_t free = _heap->free_set()->available();
65
66 size_t non_taxable = free * ShenandoahPacingCycleSlack / 100;
67 size_t taxable = free - non_taxable;
68
69 double tax = 1.0 * live / taxable; // base tax for available free space
70 tax *= 1; // mark can succeed with immediate garbage, claim all available space
71 tax *= ShenandoahPacingSurcharge; // additional surcharge to help unclutter heap
72
73 restart_with(non_taxable, tax);
74
75 log_info(gc, ergo)("Pacer for Mark. Expected Live: " SIZE_FORMAT "%s, Free: " SIZE_FORMAT "%s, "
76 "Non-Taxable: " SIZE_FORMAT "%s, Alloc Tax Rate: %.1fx",
77 byte_size_in_proper_unit(live), proper_unit_for_byte_size(live),
78 byte_size_in_proper_unit(free), proper_unit_for_byte_size(free),
79 byte_size_in_proper_unit(non_taxable), proper_unit_for_byte_size(non_taxable),
80 tax);
81 }
82
83 void ShenandoahPacer::setup_for_evac() {
84 assert(ShenandoahPacing, "Only be here when pacing is enabled");
85
86 size_t used = _heap->collection_set()->used();
87 size_t free = _heap->free_set()->available();
88
89 size_t non_taxable = free * ShenandoahPacingCycleSlack / 100;
90 size_t taxable = free - non_taxable;
91
92 double tax = 1.0 * used / taxable; // base tax for available free space
93 tax *= 2; // evac is followed by update-refs, claim 1/2 of remaining free
94 tax = MAX2<double>(1, tax); // never allocate more than GC processes during the phase
95 tax *= ShenandoahPacingSurcharge; // additional surcharge to help unclutter heap
96
97 restart_with(non_taxable, tax);
98
99 log_info(gc, ergo)("Pacer for Evacuation. Used CSet: " SIZE_FORMAT "%s, Free: " SIZE_FORMAT "%s, "
100 "Non-Taxable: " SIZE_FORMAT "%s, Alloc Tax Rate: %.1fx",
101 byte_size_in_proper_unit(used), proper_unit_for_byte_size(used),
102 byte_size_in_proper_unit(free), proper_unit_for_byte_size(free),
103 byte_size_in_proper_unit(non_taxable), proper_unit_for_byte_size(non_taxable),
104 tax);
105 }
106
107 void ShenandoahPacer::setup_for_updaterefs() {
108 assert(ShenandoahPacing, "Only be here when pacing is enabled");
109
110 size_t used = _heap->used();
111 size_t free = _heap->free_set()->available();
112
113 size_t non_taxable = free * ShenandoahPacingCycleSlack / 100;
114 size_t taxable = free - non_taxable;
115
116 double tax = 1.0 * used / taxable; // base tax for available free space
117 tax *= 1; // update-refs is the last phase, claim the remaining free
118 tax = MAX2<double>(1, tax); // never allocate more than GC processes during the phase
119 tax *= ShenandoahPacingSurcharge; // additional surcharge to help unclutter heap
120
121 restart_with(non_taxable, tax);
122
123 log_info(gc, ergo)("Pacer for Update Refs. Used: " SIZE_FORMAT "%s, Free: " SIZE_FORMAT "%s, "
124 "Non-Taxable: " SIZE_FORMAT "%s, Alloc Tax Rate: %.1fx",
125 byte_size_in_proper_unit(used), proper_unit_for_byte_size(used),
126 byte_size_in_proper_unit(free), proper_unit_for_byte_size(free),
127 byte_size_in_proper_unit(non_taxable), proper_unit_for_byte_size(non_taxable),
128 tax);
129 }
130
131 /*
132 * In idle phase, we have to pace the application to let control thread react with GC start.
133 *
134 * Here, we have rendezvous with concurrent thread that adds up the budget as it acknowledges
135 * it had seen recent allocations. It will naturally pace the allocations if control thread is
136 * not catching up. To bootstrap this feedback cycle, we need to start with some initial budget
137 * for applications to allocate at.
138 */
139
140 void ShenandoahPacer::setup_for_idle() {
141 assert(ShenandoahPacing, "Only be here when pacing is enabled");
142
143 size_t initial = _heap->max_capacity() / 100 * ShenandoahPacingIdleSlack;
144 double tax = 1;
145
146 restart_with(initial, tax);
147
148 log_info(gc, ergo)("Pacer for Idle. Initial: " SIZE_FORMAT "%s, Alloc Tax Rate: %.1fx",
149 byte_size_in_proper_unit(initial), proper_unit_for_byte_size(initial),
150 tax);
151 }
152
153 /*
154 * There is no useful notion of progress for these operations. To avoid stalling
155 * the allocators unnecessarily, allow them to run unimpeded.
156 */
157
158 void ShenandoahPacer::setup_for_reset() {
159 assert(ShenandoahPacing, "Only be here when pacing is enabled");
160
161 size_t initial = _heap->max_capacity();
162 restart_with(initial, 1.0);
163
164 log_info(gc, ergo)("Pacer for Reset. Non-Taxable: " SIZE_FORMAT "%s",
165 byte_size_in_proper_unit(initial), proper_unit_for_byte_size(initial));
166 }
167
168 size_t ShenandoahPacer::update_and_get_progress_history() {
169 if (_progress == -1) {
170 // First initialization, report some prior
171 Atomic::store(&_progress, (intptr_t)PACING_PROGRESS_ZERO);
172 return (size_t) (_heap->max_capacity() * 0.1);
173 } else {
174 // Record history, and reply historical data
175 _progress_history->add(_progress);
176 Atomic::store(&_progress, (intptr_t)PACING_PROGRESS_ZERO);
177 return (size_t) (_progress_history->avg() * HeapWordSize);
178 }
179 }
180
181 void ShenandoahPacer::restart_with(size_t non_taxable_bytes, double tax_rate) {
182 size_t initial = (size_t)(non_taxable_bytes * tax_rate) >> LogHeapWordSize;
183 STATIC_ASSERT(sizeof(size_t) <= sizeof(intptr_t));
184 Atomic::xchg(&_budget, (intptr_t)initial, memory_order_relaxed);
185 Atomic::store(&_tax_rate, tax_rate);
186 Atomic::inc(&_epoch);
187
188 // Shake up stalled waiters after budget update.
189 _need_notify_waiters.try_set();
190 }
191
192 bool ShenandoahPacer::claim_for_alloc(size_t words, bool force) {
193 assert(ShenandoahPacing, "Only be here when pacing is enabled");
194
195 intptr_t tax = MAX2<intptr_t>(1, words * Atomic::load(&_tax_rate));
196
197 intptr_t cur = 0;
198 intptr_t new_val = 0;
199 do {
200 cur = Atomic::load(&_budget);
201 if (cur < tax && !force) {
202 // Progress depleted, alas.
203 return false;
204 }
205 new_val = cur - tax;
206 } while (Atomic::cmpxchg(&_budget, cur, new_val, memory_order_relaxed) != cur);
207 return true;
208 }
209
210 void ShenandoahPacer::unpace_for_alloc(intptr_t epoch, size_t words) {
211 assert(ShenandoahPacing, "Only be here when pacing is enabled");
212
213 if (Atomic::load(&_epoch) != epoch) {
214 // Stale ticket, no need to unpace.
215 return;
216 }
217
218 size_t tax = MAX2<size_t>(1, words * Atomic::load(&_tax_rate));
219 add_budget(tax);
220 }
221
222 intptr_t ShenandoahPacer::epoch() {
223 return Atomic::load(&_epoch);
224 }
225
226 void ShenandoahPacer::pace_for_alloc(size_t words) {
227 assert(ShenandoahPacing, "Only be here when pacing is enabled");
228
229 // Fast path: try to allocate right away
230 bool claimed = claim_for_alloc(words, false);
231 if (claimed) {
232 return;
233 }
234
235 // Forcefully claim the budget: it may go negative at this point, and
236 // GC should replenish for this and subsequent allocations. After this claim,
237 // we would wait a bit until our claim is matched by additional progress,
238 // or the time budget depletes.
239 claimed = claim_for_alloc(words, true);
240 assert(claimed, "Should always succeed");
241
242 // Threads that are attaching should not block at all: they are not
243 // fully initialized yet. Blocking them would be awkward.
244 // This is probably the path that allocates the thread oop itself.
245 //
246 // Thread which is not an active Java thread should also not block.
247 // This can happen during VM init when main thread is still not an
248 // active Java thread.
249 JavaThread* current = JavaThread::current();
250 if (current->is_attaching_via_jni() ||
251 !current->is_active_Java_thread()) {
252 return;
253 }
254
255 double start = os::elapsedTime();
256
257 size_t max_ms = ShenandoahPacingMaxDelay;
258 size_t total_ms = 0;
259
260 while (true) {
261 // We could instead assist GC, but this would suffice for now.
262 size_t cur_ms = (max_ms > total_ms) ? (max_ms - total_ms) : 1;
263 wait(cur_ms);
264
265 double end = os::elapsedTime();
266 total_ms = (size_t)((end - start) * 1000);
267
268 if (total_ms > max_ms || Atomic::load(&_budget) >= 0) {
269 // Exiting if either:
270 // a) Spent local time budget to wait for enough GC progress.
271 // Breaking out and allocating anyway, which may mean we outpace GC,
272 // and start Degenerated GC cycle.
273 // b) The budget had been replenished, which means our claim is satisfied.
274 ShenandoahThreadLocalData::add_paced_time(JavaThread::current(), end - start);
275 break;
276 }
277 }
278 }
279
280 void ShenandoahPacer::wait(size_t time_ms) {
281 // Perform timed wait. It works like like sleep(), except without modifying
282 // the thread interruptible status. MonitorLocker also checks for safepoints.
283 assert(time_ms > 0, "Should not call this with zero argument, as it would stall until notify");
284 assert(time_ms <= LONG_MAX, "Sanity");
285 MonitorLocker locker(_wait_monitor);
286 _wait_monitor->wait((long)time_ms);
287 }
288
289 void ShenandoahPacer::notify_waiters() {
290 if (_need_notify_waiters.try_unset()) {
291 MonitorLocker locker(_wait_monitor);
292 _wait_monitor->notify_all();
293 }
294 }
295
296 void ShenandoahPacer::flush_stats_to_cycle() {
297 double sum = 0;
298 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
299 sum += ShenandoahThreadLocalData::paced_time(t);
300 }
301 ShenandoahHeap::heap()->phase_timings()->record_phase_time(ShenandoahPhaseTimings::pacing, sum);
302 }
303
304 void ShenandoahPacer::print_cycle_on(outputStream* out) {
305 MutexLocker lock(Threads_lock);
306
307 double now = os::elapsedTime();
308 double total = now - _last_time;
309 _last_time = now;
310
311 out->cr();
312 out->print_cr("Allocation pacing accrued:");
313
314 size_t threads_total = 0;
315 size_t threads_nz = 0;
316 double sum = 0;
317 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
318 double d = ShenandoahThreadLocalData::paced_time(t);
319 if (d > 0) {
320 threads_nz++;
321 sum += d;
322 out->print_cr(" %5.0f of %5.0f ms (%5.1f%%): %s",
323 d * 1000, total * 1000, d/total*100, t->name());
324 }
325 threads_total++;
326 ShenandoahThreadLocalData::reset_paced_time(t);
327 }
328 out->print_cr(" %5.0f of %5.0f ms (%5.1f%%): <total>",
329 sum * 1000, total * 1000, sum/total*100);
330
331 if (threads_total > 0) {
332 out->print_cr(" %5.0f of %5.0f ms (%5.1f%%): <average total>",
333 sum / threads_total * 1000, total * 1000, sum / threads_total / total * 100);
334 }
335 if (threads_nz > 0) {
336 out->print_cr(" %5.0f of %5.0f ms (%5.1f%%): <average non-zero>",
337 sum / threads_nz * 1000, total * 1000, sum / threads_nz / total * 100);
338 }
339 out->cr();
340 }