Commit | Line | Data |
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7ac06cef | 1 | Userspace RCU Implementation |
c97ae6eb | 2 | by Mathieu Desnoyers and Paul E. McKenney |
6991f61a | 3 | |
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4 | BUILDING |
5 | -------- | |
6991f61a | 6 | |
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7 | ./bootstrap (skip if using tarball) |
8 | ./configure | |
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9 | make |
10 | make install | |
9ca52251 | 11 | |
7d413817 | 12 | Hints: Forcing 32-bit build: |
c4c18179 | 13 | * CFLAGS="-m32 -g -O2" ./configure |
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14 | |
15 | Forcing 64-bit build: | |
c4c18179 | 16 | * CFLAGS="-m64 -g -O2" ./configure |
aa8c36e0 | 17 | |
f39cd442 | 18 | Forcing a 32-bit build with 386 backward compatibility: |
c4c18179 | 19 | * CFLAGS="-m32 -g -O2" ./configure --target=i386-pc-linux-gnu |
7d413817 | 20 | |
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21 | ARCHITECTURES SUPPORTED |
22 | ----------------------- | |
23 | ||
7d413817 | 24 | Currently, x86 (i386, i486, i586, i686), x86 64, PowerPC 32/64 and S390 are |
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25 | supported. The current use of sys_futex() makes it Linux-dependent, although |
26 | this portability limitation might go away in a near future by using the pthread | |
7d413817 | 27 | cond vars. |
c51e75e6 | 28 | |
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29 | QUICK START GUIDE |
30 | ----------------- | |
aa8c36e0 | 31 | |
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32 | Usage of all urcu libraries |
33 | ||
34 | * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible | |
35 | before including the urcu.h or urcu-qsbr.h header. If your application | |
36 | is distributed under another license, function calls will be generated | |
37 | instead of inlines, so your application can link with the library. | |
38 | * Linking with one of the libraries below is always necessary even for | |
39 | LGPL and GPL applications. | |
40 | ||
41 | Usage of liburcu | |
42 | ||
43 | * #include <urcu.h> | |
44 | * Link the application with "-lurcu". | |
45 | * This is the preferred version of the library, both in terms of speed | |
46 | and flexibility. Requires a signal, typically SIGUSR1. Can be | |
47 | overridden with -DSIGURCU by modifying Makefile.build.inc. | |
48 | ||
49 | Usage of liburcu-mb | |
50 | ||
51 | * #include <urcu.h> | |
256dd999 | 52 | * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB". |
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53 | * Link with "-lurcu-mb". |
54 | * This version of the urcu library does not need to | |
55 | reserve a signal number. URCU_MB uses full memory barriers for | |
56 | readers. This eliminates the need for signals but results in slower | |
57 | reads. | |
58 | ||
59 | Usage of liburcu-qsbr | |
60 | ||
61 | * #include <urcu-qsbr.h> | |
62 | * Link with "-lurcu-qsbr". | |
63 | * The QSBR flavor of RCU needs to have each reader thread executing | |
64 | rcu_quiescent_state() periodically to progress. rcu_thread_online() | |
65 | and rcu_thread_offline() can be used to mark long periods for which | |
66 | the threads are not active. It provides the fastest read-side at the | |
67 | expense of more intrusiveness in the application code. | |
68 | ||
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69 | Usage of liburcu-bp |
70 | ||
71 | * #include <urcu-bp.h> | |
72 | * Link with "-lurcu-bp". | |
73 | * The BP library flavor stands for "bulletproof". It is specifically | |
74 | designed to help tracing library to hook on applications without | |
75 | requiring to modify these applications. urcu_init(), | |
76 | rcu_register_thread() and rcu_unregister_thread() all become nops. | |
77 | The state is dealt with by the library internally at the expense of | |
78 | read-side and write-side performance. | |
79 | ||
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80 | Initialization |
81 | ||
82 | Each thread that has reader critical sections (that uses | |
83 | rcu_read_lock()/rcu_read_unlock() must first register to the URCU | |
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84 | library. This is done by calling rcu_register_thread(). Unregistration |
85 | must be performed before exiting the thread by using | |
86 | rcu_unregister_thread(). | |
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87 | |
88 | Reading | |
89 | ||
90 | Reader critical sections must be protected by locating them between | |
91 | calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock, | |
92 | rcu_dereference() may be called to read an RCU protected pointer. | |
93 | ||
94 | Writing | |
95 | ||
96 | rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere. | |
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97 | After, synchronize_rcu() must be called. When it returns, the old |
98 | values are not in usage anymore. | |
c97ae6eb | 99 | |
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100 | Usage of liburcu-defer |
101 | ||
102 | * #include <urcu-defer.h> | |
103 | * Link with "-lurcu-defer" | |
104 | * Provides call_rcu() primitive to enqueue delayed callbacks. Queued | |
105 | callbacks are executed in batch periodically after a grace period. | |
106 | Do _not_ use call_rcu() within a read-side critical section, because | |
107 | it may call synchronize_rcu() if the thread queue is full. | |
108 | ||
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109 | Being careful with signals |
110 | ||
0a1d290b | 111 | The liburcu library uses signals internally. The signal handler is |
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112 | registered with the SA_RESTART flag. However, these signals may cause |
113 | some non-restartable system calls to fail with errno = EINTR. Care | |
114 | should be taken to restart system calls manually if they fail with this | |
115 | error. A list of non-restartable system calls may be found in | |
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116 | signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU |
117 | library do not require any signal. | |
c97ae6eb | 118 | |
0a1d290b | 119 | Read-side critical sections are allowed in a signal handler with |
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120 | liburcu and liburcu-mb. Be careful, however, to disable these signals |
121 | between thread creation and calls to rcu_register_thread(), because a | |
122 | signal handler nesting on an unregistered thread would not be allowed to | |
123 | call rcu_read_lock(). | |
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125 | Read-side critical sections are _not_ allowed in a signal handler with |
126 | liburcu-qsbr, unless signals are disabled explicitly around each | |
127 | rcu_quiescent_state() calls, when threads are put offline and around | |
128 | calls to synchronize_rcu(). Even then, we do not recommend it. | |
c97ae6eb | 129 | |
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130 | Usage of DEBUG_RCU |
131 | ||
132 | DEBUG_RCU is used to add internal debugging self-checks to the | |
0a1d290b | 133 | RCU library. This define adds a performance penalty when enabled. |
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134 | Can be enabled by uncommenting the corresponding line in |
135 | Makefile.build.inc. | |
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136 | |
137 | Usage of DEBUG_YIELD | |
138 | ||
139 | DEBUG_YIELD is used to add random delays in the code for testing | |
140 | purposes. | |
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141 | |
142 | SMP support | |
143 | ||
144 | By default the library is configured to use synchronization primitives | |
145 | adequate for SMP systems. On uniprocessor systems, support for SMP | |
146 | systems can be disabled with: | |
147 | ||
148 | ./configure --disable-smp-support | |
149 | ||
150 | theoretically yielding slightly better performance. |