1/*
2 * Copyright (c) 2018, Oracle and/or its affiliates. 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#include "gc/shared/collectedHeap.hpp"
27#include "gc/shared/workerPolicy.hpp"
28#include "logging/log.hpp"
29#include "memory/universe.hpp"
30#include "runtime/os.inline.hpp"
31#include "runtime/vm_version.hpp"
32
33bool WorkerPolicy::_debug_perturbation = false;
34uint WorkerPolicy::_parallel_worker_threads = 0;
35bool WorkerPolicy::_parallel_worker_threads_initialized = false;
36
37uint WorkerPolicy::nof_parallel_worker_threads(uint num,
38 uint den,
39 uint switch_pt) {
40 if (FLAG_IS_DEFAULT(ParallelGCThreads)) {
41 assert(ParallelGCThreads == 0, "Default ParallelGCThreads is not 0");
42 uint threads;
43 // For very large machines, there are diminishing returns
44 // for large numbers of worker threads. Instead of
45 // hogging the whole system, use a fraction of the workers for every
46 // processor after the first 8. For example, on a 72 cpu machine
47 // and a chosen fraction of 5/8
48 // use 8 + (72 - 8) * (5/8) == 48 worker threads.
49 uint ncpus = (uint) os::initial_active_processor_count();
50 threads = (ncpus <= switch_pt) ?
51 ncpus :
52 (switch_pt + ((ncpus - switch_pt) * num) / den);
53#ifndef _LP64
54 // On 32-bit binaries the virtual address space available to the JVM
55 // is usually limited to 2-3 GB (depends on the platform).
56 // Do not use up address space with too many threads (stacks and per-thread
57 // data). Note that x86 apps running on Win64 have 2 stacks per thread.
58 // GC may more generally scale down threads by max heap size (etc), but the
59 // consequences of over-provisioning threads are higher on 32-bit JVMS,
60 // so add hard limit here:
61 threads = MIN2(threads, (2 * switch_pt));
62#endif
63 return threads;
64 } else {
65 return ParallelGCThreads;
66 }
67}
68
69uint WorkerPolicy::calc_parallel_worker_threads() {
70 uint den = VM_Version::parallel_worker_threads_denominator();
71 return nof_parallel_worker_threads(5, den, 8);
72}
73
74uint WorkerPolicy::parallel_worker_threads() {
75 if (!_parallel_worker_threads_initialized) {
76 if (FLAG_IS_DEFAULT(ParallelGCThreads)) {
77 _parallel_worker_threads = WorkerPolicy::calc_parallel_worker_threads();
78 } else {
79 _parallel_worker_threads = ParallelGCThreads;
80 }
81 _parallel_worker_threads_initialized = true;
82 }
83 return _parallel_worker_threads;
84}
85
86// If the number of GC threads was set on the command line, use it.
87// Else
88// Calculate the number of GC threads based on the number of Java threads.
89// Calculate the number of GC threads based on the size of the heap.
90// Use the larger.
91uint WorkerPolicy::calc_default_active_workers(uintx total_workers,
92 const uintx min_workers,
93 uintx active_workers,
94 uintx application_workers) {
95 // If the user has specifically set the number of GC threads, use them.
96
97 // If the user has turned off using a dynamic number of GC threads
98 // or the users has requested a specific number, set the active
99 // number of workers to all the workers.
100
101 uintx new_active_workers = total_workers;
102 uintx prev_active_workers = active_workers;
103 uintx active_workers_by_JT = 0;
104 uintx active_workers_by_heap_size = 0;
105
106 // Always use at least min_workers but use up to
107 // GCThreadsPerJavaThreads * application threads.
108 active_workers_by_JT =
109 MAX2((uintx) GCWorkersPerJavaThread * application_workers,
110 min_workers);
111
112 // Choose a number of GC threads based on the current size
113 // of the heap. This may be complicated because the size of
114 // the heap depends on factors such as the throughput goal.
115 // Still a large heap should be collected by more GC threads.
116 active_workers_by_heap_size =
117 MAX2((size_t) 2U, Universe::heap()->capacity() / HeapSizePerGCThread);
118
119 uintx max_active_workers =
120 MAX2(active_workers_by_JT, active_workers_by_heap_size);
121
122 new_active_workers = MIN2(max_active_workers, (uintx) total_workers);
123
124 // Increase GC workers instantly but decrease them more
125 // slowly.
126 if (new_active_workers < prev_active_workers) {
127 new_active_workers =
128 MAX2(min_workers, (prev_active_workers + new_active_workers) / 2);
129 }
130
131 // Check once more that the number of workers is within the limits.
132 assert(min_workers <= total_workers, "Minimum workers not consistent with total workers");
133 assert(new_active_workers >= min_workers, "Minimum workers not observed");
134 assert(new_active_workers <= total_workers, "Total workers not observed");
135
136 if (ForceDynamicNumberOfGCThreads) {
137 // Assume this is debugging and jiggle the number of GC threads.
138 if (new_active_workers == prev_active_workers) {
139 if (new_active_workers < total_workers) {
140 new_active_workers++;
141 } else if (new_active_workers > min_workers) {
142 new_active_workers--;
143 }
144 }
145 if (new_active_workers == total_workers) {
146 if (_debug_perturbation) {
147 new_active_workers = min_workers;
148 }
149 _debug_perturbation = !_debug_perturbation;
150 }
151 assert((new_active_workers <= ParallelGCThreads) &&
152 (new_active_workers >= min_workers),
153 "Jiggled active workers too much");
154 }
155
156 log_trace(gc, task)("WorkerPolicy::calc_default_active_workers() : "
157 "active_workers(): " UINTX_FORMAT " new_active_workers: " UINTX_FORMAT " "
158 "prev_active_workers: " UINTX_FORMAT "\n"
159 " active_workers_by_JT: " UINTX_FORMAT " active_workers_by_heap_size: " UINTX_FORMAT,
160 active_workers, new_active_workers, prev_active_workers,
161 active_workers_by_JT, active_workers_by_heap_size);
162 assert(new_active_workers > 0, "Always need at least 1");
163 return new_active_workers;
164}
165
166uint WorkerPolicy::calc_active_workers(uintx total_workers,
167 uintx active_workers,
168 uintx application_workers) {
169 // If the user has specifically set the number of GC threads, use them.
170
171 // If the user has turned off using a dynamic number of GC threads
172 // or the users has requested a specific number, set the active
173 // number of workers to all the workers.
174
175 uint new_active_workers;
176 if (!UseDynamicNumberOfGCThreads ||
177 (!FLAG_IS_DEFAULT(ParallelGCThreads) && !ForceDynamicNumberOfGCThreads)) {
178 new_active_workers = total_workers;
179 } else {
180 uintx min_workers = (total_workers == 1) ? 1 : 2;
181 new_active_workers = calc_default_active_workers(total_workers,
182 min_workers,
183 active_workers,
184 application_workers);
185 }
186 assert(new_active_workers > 0, "Always need at least 1");
187 return new_active_workers;
188}
189
190uint WorkerPolicy::calc_active_conc_workers(uintx total_workers,
191 uintx active_workers,
192 uintx application_workers) {
193 if (!UseDynamicNumberOfGCThreads ||
194 (!FLAG_IS_DEFAULT(ConcGCThreads) && !ForceDynamicNumberOfGCThreads)) {
195 return ConcGCThreads;
196 } else {
197 uint no_of_gc_threads = calc_default_active_workers(total_workers,
198 1, /* Minimum number of workers */
199 active_workers,
200 application_workers);
201 return no_of_gc_threads;
202 }
203}
204