Mon, 09 Aug 2010 05:41:05 -0700
6966222: G1: simplify TaskQueue overflow handling
Reviewed-by: tonyp, ysr
1 /*
2 * Copyright (c) 2001, 2010, 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 */
25 # include "incls/_precompiled.incl"
26 # include "incls/_taskqueue.cpp.incl"
28 #ifdef TRACESPINNING
29 uint ParallelTaskTerminator::_total_yields = 0;
30 uint ParallelTaskTerminator::_total_spins = 0;
31 uint ParallelTaskTerminator::_total_peeks = 0;
32 #endif
34 #if TASKQUEUE_STATS
35 const char * const TaskQueueStats::_names[last_stat_id] = {
36 "qpush", "qpop", "qpop-s", "qattempt", "qsteal", "opush", "omax"
37 };
39 TaskQueueStats & TaskQueueStats::operator +=(const TaskQueueStats & addend)
40 {
41 for (unsigned int i = 0; i < last_stat_id; ++i) {
42 _stats[i] += addend._stats[i];
43 }
44 return *this;
45 }
47 void TaskQueueStats::print_header(unsigned int line, outputStream* const stream,
48 unsigned int width)
49 {
50 // Use a width w: 1 <= w <= max_width
51 const unsigned int max_width = 40;
52 const unsigned int w = MAX2(MIN2(width, max_width), 1U);
54 if (line == 0) { // spaces equal in width to the header
55 const unsigned int hdr_width = w * last_stat_id + last_stat_id - 1;
56 stream->print("%*s", hdr_width, " ");
57 } else if (line == 1) { // labels
58 stream->print("%*s", w, _names[0]);
59 for (unsigned int i = 1; i < last_stat_id; ++i) {
60 stream->print(" %*s", w, _names[i]);
61 }
62 } else if (line == 2) { // dashed lines
63 char dashes[max_width + 1];
64 memset(dashes, '-', w);
65 dashes[w] = '\0';
66 stream->print("%s", dashes);
67 for (unsigned int i = 1; i < last_stat_id; ++i) {
68 stream->print(" %s", dashes);
69 }
70 }
71 }
73 void TaskQueueStats::print(outputStream* stream, unsigned int width) const
74 {
75 #define FMT SIZE_FORMAT_W(*)
76 stream->print(FMT, width, _stats[0]);
77 for (unsigned int i = 1; i < last_stat_id; ++i) {
78 stream->print(" " FMT, width, _stats[i]);
79 }
80 #undef FMT
81 }
83 #ifdef ASSERT
84 // Invariants which should hold after a TaskQueue has been emptied and is
85 // quiescent; they do not hold at arbitrary times.
86 void TaskQueueStats::verify() const
87 {
88 assert(get(push) == get(pop) + get(steal),
89 err_msg("push=" SIZE_FORMAT " pop=" SIZE_FORMAT " steal=" SIZE_FORMAT,
90 get(push), get(pop), get(steal)));
91 assert(get(pop_slow) <= get(pop),
92 err_msg("pop_slow=" SIZE_FORMAT " pop=" SIZE_FORMAT,
93 get(pop_slow), get(pop)));
94 assert(get(steal) <= get(steal_attempt),
95 err_msg("steal=" SIZE_FORMAT " steal_attempt=" SIZE_FORMAT,
96 get(steal), get(steal_attempt)));
97 assert(get(overflow) == 0 || get(push) != 0,
98 err_msg("overflow=" SIZE_FORMAT " push=" SIZE_FORMAT,
99 get(overflow), get(push)));
100 assert(get(overflow_max_len) == 0 || get(overflow) != 0,
101 err_msg("overflow_max_len=" SIZE_FORMAT " overflow=" SIZE_FORMAT,
102 get(overflow_max_len), get(overflow)));
103 }
104 #endif // ASSERT
105 #endif // TASKQUEUE_STATS
107 int TaskQueueSetSuper::randomParkAndMiller(int *seed0) {
108 const int a = 16807;
109 const int m = 2147483647;
110 const int q = 127773; /* m div a */
111 const int r = 2836; /* m mod a */
112 assert(sizeof(int) == 4, "I think this relies on that");
113 int seed = *seed0;
114 int hi = seed / q;
115 int lo = seed % q;
116 int test = a * lo - r * hi;
117 if (test > 0)
118 seed = test;
119 else
120 seed = test + m;
121 *seed0 = seed;
122 return seed;
123 }
125 ParallelTaskTerminator::
126 ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set) :
127 _n_threads(n_threads),
128 _queue_set(queue_set),
129 _offered_termination(0) {}
131 bool ParallelTaskTerminator::peek_in_queue_set() {
132 return _queue_set->peek();
133 }
135 void ParallelTaskTerminator::yield() {
136 assert(_offered_termination <= _n_threads, "Invariant");
137 os::yield();
138 }
140 void ParallelTaskTerminator::sleep(uint millis) {
141 assert(_offered_termination <= _n_threads, "Invariant");
142 os::sleep(Thread::current(), millis, false);
143 }
145 bool
146 ParallelTaskTerminator::offer_termination(TerminatorTerminator* terminator) {
147 assert(_offered_termination < _n_threads, "Invariant");
148 Atomic::inc(&_offered_termination);
150 uint yield_count = 0;
151 // Number of hard spin loops done since last yield
152 uint hard_spin_count = 0;
153 // Number of iterations in the hard spin loop.
154 uint hard_spin_limit = WorkStealingHardSpins;
156 // If WorkStealingSpinToYieldRatio is 0, no hard spinning is done.
157 // If it is greater than 0, then start with a small number
158 // of spins and increase number with each turn at spinning until
159 // the count of hard spins exceeds WorkStealingSpinToYieldRatio.
160 // Then do a yield() call and start spinning afresh.
161 if (WorkStealingSpinToYieldRatio > 0) {
162 hard_spin_limit = WorkStealingHardSpins >> WorkStealingSpinToYieldRatio;
163 hard_spin_limit = MAX2(hard_spin_limit, 1U);
164 }
165 // Remember the initial spin limit.
166 uint hard_spin_start = hard_spin_limit;
168 // Loop waiting for all threads to offer termination or
169 // more work.
170 while (true) {
171 assert(_offered_termination <= _n_threads, "Invariant");
172 // Are all threads offering termination?
173 if (_offered_termination == _n_threads) {
174 return true;
175 } else {
176 // Look for more work.
177 // Periodically sleep() instead of yield() to give threads
178 // waiting on the cores the chance to grab this code
179 if (yield_count <= WorkStealingYieldsBeforeSleep) {
180 // Do a yield or hardspin. For purposes of deciding whether
181 // to sleep, count this as a yield.
182 yield_count++;
184 // Periodically call yield() instead spinning
185 // After WorkStealingSpinToYieldRatio spins, do a yield() call
186 // and reset the counts and starting limit.
187 if (hard_spin_count > WorkStealingSpinToYieldRatio) {
188 yield();
189 hard_spin_count = 0;
190 hard_spin_limit = hard_spin_start;
191 #ifdef TRACESPINNING
192 _total_yields++;
193 #endif
194 } else {
195 // Hard spin this time
196 // Increase the hard spinning period but only up to a limit.
197 hard_spin_limit = MIN2(2*hard_spin_limit,
198 (uint) WorkStealingHardSpins);
199 for (uint j = 0; j < hard_spin_limit; j++) {
200 SpinPause();
201 }
202 hard_spin_count++;
203 #ifdef TRACESPINNING
204 _total_spins++;
205 #endif
206 }
207 } else {
208 if (PrintGCDetails && Verbose) {
209 gclog_or_tty->print_cr("ParallelTaskTerminator::offer_termination() "
210 "thread %d sleeps after %d yields",
211 Thread::current(), yield_count);
212 }
213 yield_count = 0;
214 // A sleep will cause this processor to seek work on another processor's
215 // runqueue, if it has nothing else to run (as opposed to the yield
216 // which may only move the thread to the end of the this processor's
217 // runqueue).
218 sleep(WorkStealingSleepMillis);
219 }
221 #ifdef TRACESPINNING
222 _total_peeks++;
223 #endif
224 if (peek_in_queue_set() ||
225 (terminator != NULL && terminator->should_exit_termination())) {
226 Atomic::dec(&_offered_termination);
227 assert(_offered_termination < _n_threads, "Invariant");
228 return false;
229 }
230 }
231 }
232 }
234 #ifdef TRACESPINNING
235 void ParallelTaskTerminator::print_termination_counts() {
236 gclog_or_tty->print_cr("ParallelTaskTerminator Total yields: %lld "
237 "Total spins: %lld Total peeks: %lld",
238 total_yields(),
239 total_spins(),
240 total_peeks());
241 }
242 #endif
244 void ParallelTaskTerminator::reset_for_reuse() {
245 if (_offered_termination != 0) {
246 assert(_offered_termination == _n_threads,
247 "Terminator may still be in use");
248 _offered_termination = 0;
249 }
250 }
252 #ifdef ASSERT
253 bool ObjArrayTask::is_valid() const {
254 return _obj != NULL && _obj->is_objArray() && _index > 0 &&
255 _index < objArrayOop(_obj)->length();
256 }
257 #endif // ASSERT