Mercurial > hg > truffle
annotate src/share/vm/runtime/biasedLocking.hpp @ 1711:a6bff45449bc
6973570: OrderAccess::storestore() scales poorly on multi-socket x64 and sparc: cache-line ping-ponging
Summary: volatile store to static variable removed in favour of a volatile store to stack to avoid excessive cache coherency traffic; verified that the volatile store is not elided by any of our current compilers.
Reviewed-by: dholmes, dice, jcoomes, kvn
author | ysr |
---|---|
date | Tue, 10 Aug 2010 14:53:35 -0700 |
parents | c18cbe5936b8 |
children | f95d63e2154a |
rev | line source |
---|---|
0 | 1 /* |
1552
c18cbe5936b8
6941466: Oracle rebranding changes for Hotspot repositories
trims
parents:
0
diff
changeset
|
2 * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved. |
0 | 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 * | |
1552
c18cbe5936b8
6941466: Oracle rebranding changes for Hotspot repositories
trims
parents:
0
diff
changeset
|
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
c18cbe5936b8
6941466: Oracle rebranding changes for Hotspot repositories
trims
parents:
0
diff
changeset
|
20 * or visit www.oracle.com if you need additional information or have any |
c18cbe5936b8
6941466: Oracle rebranding changes for Hotspot repositories
trims
parents:
0
diff
changeset
|
21 * questions. |
0 | 22 * |
23 */ | |
24 | |
25 // This class describes operations to implement Store-Free Biased | |
26 // Locking. The high-level properties of the scheme are similar to | |
27 // IBM's lock reservation, Dice-Moir-Scherer QR locks, and other biased | |
28 // locking mechanisms. The principal difference is in the handling of | |
29 // recursive locking which is how this technique achieves a more | |
30 // efficient fast path than these other schemes. | |
31 // | |
32 // The basic observation is that in HotSpot's current fast locking | |
33 // scheme, recursive locking (in the fast path) causes no update to | |
34 // the object header. The recursion is described simply by stack | |
35 // records containing a specific value (NULL). Only the last unlock by | |
36 // a given thread causes an update to the object header. | |
37 // | |
38 // This observation, coupled with the fact that HotSpot only compiles | |
39 // methods for which monitor matching is obeyed (and which therefore | |
40 // can not throw IllegalMonitorStateException), implies that we can | |
41 // completely eliminate modifications to the object header for | |
42 // recursive locking in compiled code, and perform similar recursion | |
43 // checks and throwing of IllegalMonitorStateException in the | |
44 // interpreter with little or no impact on the performance of the fast | |
45 // path. | |
46 // | |
47 // The basic algorithm is as follows (note, see below for more details | |
48 // and information). A pattern in the low three bits is reserved in | |
49 // the object header to indicate whether biasing of a given object's | |
50 // lock is currently being done or is allowed at all. If the bias | |
51 // pattern is present, the contents of the rest of the header are | |
52 // either the JavaThread* of the thread to which the lock is biased, | |
53 // or NULL, indicating that the lock is "anonymously biased". The | |
54 // first thread which locks an anonymously biased object biases the | |
55 // lock toward that thread. If another thread subsequently attempts to | |
56 // lock the same object, the bias is revoked. | |
57 // | |
58 // Because there are no updates to the object header at all during | |
59 // recursive locking while the lock is biased, the biased lock entry | |
60 // code is simply a test of the object header's value. If this test | |
61 // succeeds, the lock has been acquired by the thread. If this test | |
62 // fails, a bit test is done to see whether the bias bit is still | |
63 // set. If not, we fall back to HotSpot's original CAS-based locking | |
64 // scheme. If it is set, we attempt to CAS in a bias toward this | |
65 // thread. The latter operation is expected to be the rarest operation | |
66 // performed on these locks. We optimistically expect the biased lock | |
67 // entry to hit most of the time, and want the CAS-based fallthrough | |
68 // to occur quickly in the situations where the bias has been revoked. | |
69 // | |
70 // Revocation of the lock's bias is fairly straightforward. We want to | |
71 // restore the object's header and stack-based BasicObjectLocks and | |
72 // BasicLocks to the state they would have been in had the object been | |
73 // locked by HotSpot's usual fast locking scheme. To do this, we bring | |
74 // the system to a safepoint and walk the stack of the thread toward | |
75 // which the lock is biased. We find all of the lock records on the | |
76 // stack corresponding to this object, in particular the first / | |
77 // "highest" record. We fill in the highest lock record with the | |
78 // object's displaced header (which is a well-known value given that | |
79 // we don't maintain an identity hash nor age bits for the object | |
80 // while it's in the biased state) and all other lock records with 0, | |
81 // the value for recursive locks. When the safepoint is released, the | |
82 // formerly-biased thread and all other threads revert back to | |
83 // HotSpot's CAS-based locking. | |
84 // | |
85 // This scheme can not handle transfers of biases of single objects | |
86 // from thread to thread efficiently, but it can handle bulk transfers | |
87 // of such biases, which is a usage pattern showing up in some | |
88 // applications and benchmarks. We implement "bulk rebias" and "bulk | |
89 // revoke" operations using a "bias epoch" on a per-data-type basis. | |
90 // If too many bias revocations are occurring for a particular data | |
91 // type, the bias epoch for the data type is incremented at a | |
92 // safepoint, effectively meaning that all previous biases are | |
93 // invalid. The fast path locking case checks for an invalid epoch in | |
94 // the object header and attempts to rebias the object with a CAS if | |
95 // found, avoiding safepoints or bulk heap sweeps (the latter which | |
96 // was used in a prior version of this algorithm and did not scale | |
97 // well). If too many bias revocations persist, biasing is completely | |
98 // disabled for the data type by resetting the prototype header to the | |
99 // unbiased markOop. The fast-path locking code checks to see whether | |
100 // the instance's bias pattern differs from the prototype header's and | |
101 // causes the bias to be revoked without reaching a safepoint or, | |
102 // again, a bulk heap sweep. | |
103 | |
104 // Biased locking counters | |
105 class BiasedLockingCounters VALUE_OBJ_CLASS_SPEC { | |
106 private: | |
107 int _total_entry_count; | |
108 int _biased_lock_entry_count; | |
109 int _anonymously_biased_lock_entry_count; | |
110 int _rebiased_lock_entry_count; | |
111 int _revoked_lock_entry_count; | |
112 int _fast_path_entry_count; | |
113 int _slow_path_entry_count; | |
114 | |
115 public: | |
116 BiasedLockingCounters() : | |
117 _total_entry_count(0), | |
118 _biased_lock_entry_count(0), | |
119 _anonymously_biased_lock_entry_count(0), | |
120 _rebiased_lock_entry_count(0), | |
121 _revoked_lock_entry_count(0), | |
122 _fast_path_entry_count(0), | |
123 _slow_path_entry_count(0) {} | |
124 | |
125 int slow_path_entry_count(); // Compute this field if necessary | |
126 | |
127 int* total_entry_count_addr() { return &_total_entry_count; } | |
128 int* biased_lock_entry_count_addr() { return &_biased_lock_entry_count; } | |
129 int* anonymously_biased_lock_entry_count_addr() { return &_anonymously_biased_lock_entry_count; } | |
130 int* rebiased_lock_entry_count_addr() { return &_rebiased_lock_entry_count; } | |
131 int* revoked_lock_entry_count_addr() { return &_revoked_lock_entry_count; } | |
132 int* fast_path_entry_count_addr() { return &_fast_path_entry_count; } | |
133 int* slow_path_entry_count_addr() { return &_slow_path_entry_count; } | |
134 | |
135 bool nonzero() { return _total_entry_count > 0; } | |
136 | |
137 void print_on(outputStream* st); | |
138 void print() { print_on(tty); } | |
139 }; | |
140 | |
141 | |
142 class BiasedLocking : AllStatic { | |
143 private: | |
144 static BiasedLockingCounters _counters; | |
145 | |
146 public: | |
147 static int* total_entry_count_addr(); | |
148 static int* biased_lock_entry_count_addr(); | |
149 static int* anonymously_biased_lock_entry_count_addr(); | |
150 static int* rebiased_lock_entry_count_addr(); | |
151 static int* revoked_lock_entry_count_addr(); | |
152 static int* fast_path_entry_count_addr(); | |
153 static int* slow_path_entry_count_addr(); | |
154 | |
155 enum Condition { | |
156 NOT_BIASED = 1, | |
157 BIAS_REVOKED = 2, | |
158 BIAS_REVOKED_AND_REBIASED = 3 | |
159 }; | |
160 | |
161 // This initialization routine should only be called once and | |
162 // schedules a PeriodicTask to turn on biased locking a few seconds | |
163 // into the VM run to avoid startup time regressions | |
164 static void init(); | |
165 | |
166 // This provides a global switch for leaving biased locking disabled | |
167 // for the first part of a run and enabling it later | |
168 static bool enabled(); | |
169 | |
170 // This should be called by JavaThreads to revoke the bias of an object | |
171 static Condition revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS); | |
172 | |
173 // These do not allow rebiasing; they are used by deoptimization to | |
174 // ensure that monitors on the stack can be migrated | |
175 static void revoke(GrowableArray<Handle>* objs); | |
176 static void revoke_at_safepoint(Handle obj); | |
177 static void revoke_at_safepoint(GrowableArray<Handle>* objs); | |
178 | |
179 static void print_counters() { _counters.print(); } | |
180 static BiasedLockingCounters* counters() { return &_counters; } | |
181 | |
182 // These routines are GC-related and should not be called by end | |
183 // users. GCs which do not do preservation of mark words do not need | |
184 // to call these routines. | |
185 static void preserve_marks(); | |
186 static void restore_marks(); | |
187 }; |