X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=README;h=f9437dba2857856b726cc4539b6deeafaf09f668;hp=0ec723dea10186d13e6c11705e18a0c8149ae288;hb=64c4cafd597aff7423be003dcf41735904126f66;hpb=cee02f0ab0a6766662490f2d815d487c098c17b1 diff --git a/README b/README index 0ec723d..f9437db 100644 --- a/README +++ b/README @@ -1,21 +1,87 @@ -Userspace RCU Implementatation +Userspace RCU Implementation by Mathieu Desnoyers and Paul E. McKenney BUILDING -------- + ./bootstrap (skip if using tarball) + ./configure make make install - + + Note: Forcing 32-bit build: + * CFLAGS=-m32 ./configure + + Forcing 64-bit build: + * CFLAGS=-m64 ./configure + +ARCHITECTURES SUPPORTED +----------------------- + +Currently, x86 (only P6+), x86 64, PowerPC 32/64 and S390 are +supported. The current use of sys_futex() makes it Linux-dependent, although +this portability limitation might go away in a near future by using the pthread +cond vars. Also, the restriction against i386, i486 and Pentium might go away if +we integrate some of glibc runtime CPU-detection tests. QUICK START GUIDE ----------------- +Usage of all urcu libraries + + * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible + before including the urcu.h or urcu-qsbr.h header. If your application + is distributed under another license, function calls will be generated + instead of inlines, so your application can link with the library. + * Linking with one of the libraries below is always necessary even for + LGPL and GPL applications. + +Usage of liburcu + + * #include + * Link the application with "-lurcu". + * This is the preferred version of the library, both in terms of speed + and flexibility. Requires a signal, typically SIGUSR1. Can be + overridden with -DSIGURCU by modifying Makefile.build.inc. + +Usage of liburcu-mb + + * #include + * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB". + * Link with "-lurcu-mb". + * This version of the urcu library does not need to + reserve a signal number. URCU_MB uses full memory barriers for + readers. This eliminates the need for signals but results in slower + reads. + +Usage of liburcu-qsbr + + * #include + * Link with "-lurcu-qsbr". + * The QSBR flavor of RCU needs to have each reader thread executing + rcu_quiescent_state() periodically to progress. rcu_thread_online() + and rcu_thread_offline() can be used to mark long periods for which + the threads are not active. It provides the fastest read-side at the + expense of more intrusiveness in the application code. + +Usage of liburcu-bp + + * #include + * Link with "-lurcu-bp". + * The BP library flavor stands for "bulletproof". It is specifically + designed to help tracing library to hook on applications without + requiring to modify these applications. urcu_init(), + rcu_register_thread() and rcu_unregister_thread() all become nops. + The state is dealt with by the library internally at the expense of + read-side and write-side performance. + Initialization Each thread that has reader critical sections (that uses rcu_read_lock()/rcu_read_unlock() must first register to the URCU - library. This is done by calling rcu_register_thread(). + library. This is done by calling rcu_register_thread(). Unregistration + must be performed before exiting the thread by using + rcu_unregister_thread(). Reading @@ -29,30 +95,42 @@ Writing After, synchronize_rcu() must be called. When it returns, the old values are not in usage anymore. +Usage of liburcu-defer + + * #include + * Link with "-lurcu-defer" + * Provides call_rcu() primitive to enqueue delayed callbacks. Queued + callbacks are executed in batch periodically after a grace period. + Do _not_ use call_rcu() within a read-side critical section, because + it may call synchronize_rcu() if the thread queue is full. + Being careful with signals - The library uses signals internally. The signal handler is + The liburcu library uses signals internally. The signal handler is registered with the SA_RESTART flag. However, these signals may cause some non-restartable system calls to fail with errno = EINTR. Care should be taken to restart system calls manually if they fail with this error. A list of non-restartable system calls may be found in - signal(7). To ensure the Userspace RCU library does not use signals, - define CONFIG_URCU_AVOID_SIGNALS at compile-time. - - Read-side critical sections can sit in a signal handler. Be careful, - however, to disable these signals between thread creation and calls to - rcu_register_thread(), because a signal handler nesting on an - unregistered thread would not be allowed to call rcu_read_lock(). + signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU + library do not require any signal. -Usage of CONFIG_URCU_AVOID_SIGNALS + Read-side critical sections are allowed in a signal handler with + liburcu and liburcu-mb. Be careful, however, to disable these signals + between thread creation and calls to rcu_register_thread(), because a + signal handler nesting on an unregistered thread would not be allowed to + call rcu_read_lock(). - CONFIG_URCU_AVOID_SIGNALS uses full SMP barriers for readers. This - eliminates the need for signals but results in slower reads. + Read-side critical sections are _not_ allowed in a signal handler with + liburcu-qsbr, unless signals are disabled explicitly around each + rcu_quiescent_state() calls, when threads are put offline and around + calls to synchronize_rcu(). Even then, we do not recommend it. Usage of DEBUG_RCU DEBUG_RCU is used to add internal debugging self-checks to the - RCU library. This define adds a performance penality when enabled. + RCU library. This define adds a performance penalty when enabled. + Can be enabled by uncommenting the corresponding line in + Makefile.build.inc. Usage of DEBUG_YIELD