Commit | Line | Data |
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7ac06cef | 1 | Userspace RCU Implementation |
c97ae6eb | 2 | by Mathieu Desnoyers and Paul E. McKenney |
6991f61a | 3 | |
c97ae6eb PMF |
4 | BUILDING |
5 | -------- | |
6991f61a | 6 | |
48d848c7 PMF |
7 | ./bootstrap (skip if using tarball) |
8 | ./configure | |
c97ae6eb PMF |
9 | make |
10 | make install | |
9ca52251 | 11 | |
7d413817 | 12 | Hints: Forcing 32-bit build: |
c4c18179 | 13 | * CFLAGS="-m32 -g -O2" ./configure |
9ca52251 MD |
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: |
c5b9f8ff | 19 | * CFLAGS="-m32 -g -O2" ./configure --host=i386-pc-linux-gnu |
7d413817 | 20 | |
795d506a MD |
21 | Forcing a 32-bit build for Sparcv9 (typical for Sparc v9) |
22 | * CFLAGS="-m32 -Wa,-Av9a -g -O2" ./configure | |
23 | ||
c51e75e6 MD |
24 | ARCHITECTURES SUPPORTED |
25 | ----------------------- | |
26 | ||
c0a68bfa | 27 | Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x |
795d506a | 28 | and Sparcv9 32/64 are supported. Only tested on Linux so far, but should |
c0a68bfa | 29 | theoretically work on other operating systems. |
c51e75e6 | 30 | |
c97ae6eb PMF |
31 | QUICK START GUIDE |
32 | ----------------- | |
aa8c36e0 | 33 | |
0a1d290b MD |
34 | Usage of all urcu libraries |
35 | ||
36 | * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible | |
37 | before including the urcu.h or urcu-qsbr.h header. If your application | |
38 | is distributed under another license, function calls will be generated | |
39 | instead of inlines, so your application can link with the library. | |
40 | * Linking with one of the libraries below is always necessary even for | |
41 | LGPL and GPL applications. | |
42 | ||
43 | Usage of liburcu | |
44 | ||
45 | * #include <urcu.h> | |
46 | * Link the application with "-lurcu". | |
fdf01eed MD |
47 | * This is the preferred version of the library, in terms of |
48 | grace-period detection speed, read-side speed and flexibility. | |
49 | Dynamically detects kernel support for sys_membarrier(). Falls back | |
50 | on urcu-mb scheme if support is not present, which has slower | |
51 | read-side. | |
0a1d290b MD |
52 | |
53 | Usage of liburcu-qsbr | |
54 | ||
55 | * #include <urcu-qsbr.h> | |
56 | * Link with "-lurcu-qsbr". | |
57 | * The QSBR flavor of RCU needs to have each reader thread executing | |
58 | rcu_quiescent_state() periodically to progress. rcu_thread_online() | |
59 | and rcu_thread_offline() can be used to mark long periods for which | |
60 | the threads are not active. It provides the fastest read-side at the | |
61 | expense of more intrusiveness in the application code. | |
62 | ||
fdf01eed MD |
63 | Usage of liburcu-mb |
64 | ||
65 | * #include <urcu.h> | |
66 | * Compile any _LGPL_SOURCE code using this library with "-DRCU_MB". | |
67 | * Link with "-lurcu-mb". | |
68 | * This version of the urcu library uses memory barriers on the writer | |
69 | and reader sides. This results in faster grace-period detection, but | |
70 | results in slower reads. | |
71 | ||
72 | Usage of liburcu-signal | |
73 | ||
74 | * #include <urcu-signal.h> | |
75 | * Link the application with "-lurcu-signal". | |
76 | * Version of the library that requires a signal, typically SIGUSR1. Can | |
77 | be overridden with -DSIGRCU by modifying Makefile.build.inc. | |
78 | ||
fdee2e6d MD |
79 | Usage of liburcu-bp |
80 | ||
81 | * #include <urcu-bp.h> | |
82 | * Link with "-lurcu-bp". | |
83 | * The BP library flavor stands for "bulletproof". It is specifically | |
84 | designed to help tracing library to hook on applications without | |
02be5561 | 85 | requiring to modify these applications. rcu_init(), |
fdee2e6d MD |
86 | rcu_register_thread() and rcu_unregister_thread() all become nops. |
87 | The state is dealt with by the library internally at the expense of | |
88 | read-side and write-side performance. | |
89 | ||
c97ae6eb PMF |
90 | Initialization |
91 | ||
92 | Each thread that has reader critical sections (that uses | |
93 | rcu_read_lock()/rcu_read_unlock() must first register to the URCU | |
4c1471de MD |
94 | library. This is done by calling rcu_register_thread(). Unregistration |
95 | must be performed before exiting the thread by using | |
96 | rcu_unregister_thread(). | |
c97ae6eb PMF |
97 | |
98 | Reading | |
99 | ||
100 | Reader critical sections must be protected by locating them between | |
101 | calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock, | |
102 | rcu_dereference() may be called to read an RCU protected pointer. | |
103 | ||
104 | Writing | |
105 | ||
106 | rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere. | |
9fb223da MD |
107 | After, synchronize_rcu() must be called. When it returns, the old |
108 | values are not in usage anymore. | |
c97ae6eb | 109 | |
ec4e58a3 MD |
110 | Usage of liburcu-defer |
111 | ||
112 | * #include <urcu-defer.h> | |
24c9669d MD |
113 | * Link with "-lurcu-defer", and also with one of the urcu library |
114 | (either urcu, urcu-bp, urcu-mb or urcu-qsbr). | |
632dd6ba | 115 | * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued |
ec4e58a3 | 116 | callbacks are executed in batch periodically after a grace period. |
632dd6ba | 117 | Do _not_ use defer_rcu() within a read-side critical section, because |
ec4e58a3 | 118 | it may call synchronize_rcu() if the thread queue is full. |
ec8e44cf MD |
119 | * Provides defer_rcu_ratelimit() primitive, which acts just like |
120 | defer_rcu(), but takes an additional rate limiter callback forcing | |
121 | synchronized callback execution of the limiter returns non-zero. | |
83dd659a MD |
122 | * Requires that rcu_defer_barrier() must be called in library destructor |
123 | if a library queues callbacks and is expected to be unloaded with | |
124 | dlclose(). | |
9c55af9f MD |
125 | * Its API is currently experimental. It may change in future library |
126 | releases. | |
ec4e58a3 | 127 | |
dd052bd3 PMF |
128 | Being careful with signals |
129 | ||
0a1d290b | 130 | The liburcu library uses signals internally. The signal handler is |
dd052bd3 PMF |
131 | registered with the SA_RESTART flag. However, these signals may cause |
132 | some non-restartable system calls to fail with errno = EINTR. Care | |
133 | should be taken to restart system calls manually if they fail with this | |
134 | error. A list of non-restartable system calls may be found in | |
0a1d290b MD |
135 | signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU |
136 | library do not require any signal. | |
c97ae6eb | 137 | |
0a1d290b | 138 | Read-side critical sections are allowed in a signal handler with |
7ac06cef MD |
139 | liburcu and liburcu-mb. Be careful, however, to disable these signals |
140 | between thread creation and calls to rcu_register_thread(), because a | |
141 | signal handler nesting on an unregistered thread would not be allowed to | |
142 | call rcu_read_lock(). | |
cee02f0a | 143 | |
0a1d290b MD |
144 | Read-side critical sections are _not_ allowed in a signal handler with |
145 | liburcu-qsbr, unless signals are disabled explicitly around each | |
146 | rcu_quiescent_state() calls, when threads are put offline and around | |
147 | calls to synchronize_rcu(). Even then, we do not recommend it. | |
c97ae6eb | 148 | |
955f5e52 MD |
149 | Interaction with mutexes |
150 | ||
151 | One must be careful to do not cause deadlocks due to interaction of | |
152 | synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu() | |
153 | is called with a mutex held, this mutex (or any mutex which has this | |
154 | mutex in its dependency chain) should not be acquired from within a RCU | |
155 | read-side critical section. | |
156 | ||
cee02f0a MD |
157 | Usage of DEBUG_RCU |
158 | ||
159 | DEBUG_RCU is used to add internal debugging self-checks to the | |
0a1d290b | 160 | RCU library. This define adds a performance penalty when enabled. |
fb6e510b MD |
161 | Can be enabled by uncommenting the corresponding line in |
162 | Makefile.build.inc. | |
c97ae6eb PMF |
163 | |
164 | Usage of DEBUG_YIELD | |
165 | ||
166 | DEBUG_YIELD is used to add random delays in the code for testing | |
167 | purposes. | |
7d413817 MD |
168 | |
169 | SMP support | |
170 | ||
171 | By default the library is configured to use synchronization primitives | |
172 | adequate for SMP systems. On uniprocessor systems, support for SMP | |
173 | systems can be disabled with: | |
174 | ||
175 | ./configure --disable-smp-support | |
176 | ||
177 | theoretically yielding slightly better performance. |