X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=README;h=796b9cfcd4dbad1d87775b22e53559dcdf7df7ed;hp=f9af1eb483d83d3cee27625efc0eaa5c48dbbe3e;hb=eaf2c3f4b9041d2a6a85d7f9e56f6014603367d4;hpb=fb6e510b9ae45b9b984b4646b4be6b9d7a2bbf7c diff --git a/README b/README index f9af1eb..796b9cf 100644 --- a/README +++ b/README @@ -1,21 +1,114 @@ -Userspace RCU Implementatation +Userspace RCU Implementation by Mathieu Desnoyers and Paul E. McKenney BUILDING -------- + ./bootstrap (skip if using tarball) + ./configure make make install - + + Hints: Forcing 32-bit build: + * CFLAGS="-m32 -g -O2" ./configure + + Forcing 64-bit build: + * CFLAGS="-m64 -g -O2" ./configure + + Forcing a 32-bit build with 386 backward compatibility: + * CFLAGS="-m32 -g -O2" ./configure --host=i386-pc-linux-gnu + + Forcing a 32-bit build for Sparcv9 (typical for Sparc v9) + * CFLAGS="-m32 -Wa,-Av9a -g -O2" ./configure + +ARCHITECTURES SUPPORTED +----------------------- + +Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x +ARMv7l, Alpha, ia64 and Sparcv9 32/64 are supported. Only tested on Linux so +far, but should theoretically work on other operating systems. + +ARMv7l depends on running a Linux kernel 2.6.15 or better. + +The gcc compiler versions 3.3, 3.4, 4.0, 4.1, 4.2, 4.3, 4.4 and 4.5 are +supported, with the following exceptions: + +- gcc 3.3 and 3.4 have a bug that prevents them from generating volatile + accesses to offsets in a TLS structure on 32-bit x86. These versions are + therefore not compatible with liburcu on x86 32-bit (i386, i486, i586, i686). + The problem has been reported to the gcc community: + http://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg281255.html +- Alpha, ia64 and ARMv7l architectures depend on 4.x gcc with atomic builtins + support. + 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, in terms of + grace-period detection speed, read-side speed and flexibility. + Dynamically detects kernel support for sys_membarrier(). Falls back + on urcu-mb scheme if support is not present, which has slower + read-side. + +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-mb + + * #include + * Compile any _LGPL_SOURCE code using this library with "-DRCU_MB". + * Link with "-lurcu-mb". + * This version of the urcu library uses memory barriers on the writer + and reader sides. This results in faster grace-period detection, but + results in slower reads. + +Usage of liburcu-signal + + * #include + * Compile any _LGPL_SOURCE code using this library with "-DRCU_SIGNAL". + * Link the application with "-lurcu-signal". + * Version of the library that requires a signal, typically SIGUSR1. Can + be overridden with -DSIGRCU by modifying Makefile.build.inc. + +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. rcu_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 +122,57 @@ 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", and also with one of the urcu library + (either urcu, urcu-bp, urcu-mb or urcu-qsbr). + * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued + callbacks are executed in batch periodically after a grace period. + Do _not_ use defer_rcu() within a read-side critical section, because + it may call synchronize_rcu() if the thread queue is full. + * Provides defer_rcu_ratelimit() primitive, which acts just like + defer_rcu(), but takes an additional rate limiter callback forcing + synchronized callback execution of the limiter returns non-zero. + * Requires that rcu_defer_barrier() must be called in library destructor + if a library queues callbacks and is expected to be unloaded with + dlclose(). + * Its API is currently experimental. It may change in future library + releases. + 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. + signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU + library do not require any signal. + + 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(). - 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(). + 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 CONFIG_URCU_AVOID_SIGNALS +Interaction with mutexes - CONFIG_URCU_AVOID_SIGNALS uses full SMP barriers for readers. This - eliminates the need for signals but results in slower reads. + One must be careful to do not cause deadlocks due to interaction of + synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu() + is called with a mutex held, this mutex (or any mutex which has this + mutex in its dependency chain) should not be acquired from within a RCU + read-side critical section. 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. @@ -60,3 +180,13 @@ Usage of DEBUG_YIELD DEBUG_YIELD is used to add random delays in the code for testing purposes. + +SMP support + + By default the library is configured to use synchronization primitives + adequate for SMP systems. On uniprocessor systems, support for SMP + systems can be disabled with: + + ./configure --disable-smp-support + + theoretically yielding slightly better performance.