X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=README;h=1e76f2d1b098bb9579d573fcf8f36211c3c7c5f9;hp=e5c04b179cae49d202a49809d09a76f714ada711;hb=bc2433a9853a945a825c244e9ccfe341b73b2ceb;hpb=ec4e58a3aba2084440012f8ccac3a31eb6101183 diff --git a/README b/README index e5c04b1..1e76f2d 100644 --- a/README +++ b/README @@ -4,11 +4,46 @@ by Mathieu Desnoyers and Paul E. McKenney BUILDING -------- + ./bootstrap (skip if using tarball) + ./configure make - #force 32-bit build with: make -f Makefile32 - #force 64-bit build with: make -f Makefile64 make install - + ldconfig + + 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, +ARM, Alpha, ia64 and Sparcv9 32/64 are supported. Only tested on Linux so +far, but should theoretically work on other operating systems. + +ARM 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 +- gcc 3.3 cannot match the "xchg" instruction on 32-bit x86 build. + See: http://kerneltrap.org/node/7507 +- Alpha, ia64 and ARM architectures depend on 4.x gcc with atomic builtins + support. + QUICK START GUIDE ----------------- @@ -26,19 +61,11 @@ 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. + * 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 @@ -50,6 +77,34 @@ Usage of liburcu-qsbr 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 @@ -72,12 +127,36 @@ Writing Usage of liburcu-defer - * #include - * Link with "-lurcu-defer" - * Provides call_rcu() primitive to enqueue delayed callbacks. Queued + * Follow instructions for either liburcu, liburcu-qsbr, + liburcu-mb, liburcu-signal, or liburcu-bp above. + The liburcu-defer functionality is pulled into each of + those library modules. + * Provides defer_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 + Do _not_ use defer_rcu() within a read-side critical section, because it may call synchronize_rcu() if the thread queue is full. + This can lead to deadlock or worse. + * 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. + +Usage of urcu-call-rcu + + * Follow instructions for either liburcu, liburcu-qsbr, + liburcu-mb, liburcu-signal, or liburcu-bp above. + The urcu-call-rcu functionality is provided for each of + these library modules. + * Provides the call_rcu() primitive to enqueue delayed callbacks + in a manner similar to defer_rcu(), but without ever delaying + for a grace period. On the other hand, call_rcu()'s best-case + overhead is not quite as good as that of defer_rcu(). + * Provides call_rcu() to allow asynchronous handling of RCU + grace periods. A number of additional functions are provided + to manage the helper threads used by call_rcu(), but reasonable + defaults are used if these additional functions are not invoked. + See API.txt for more details. Being careful with signals @@ -100,6 +179,14 @@ Being careful with signals rcu_quiescent_state() calls, when threads are put offline and around calls to synchronize_rcu(). Even then, we do not recommend it. +Interaction with mutexes + + 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 @@ -111,3 +198,34 @@ 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. + +Interaction with fork() + + Special care must be taken for applications performing fork() without + any following exec(). This is caused by the fact that Linux only clones + the thread calling fork(), and thus never replicates any of the other + parent thread into the child process. Most liburcu implementations + require that all registrations (as reader, defer_rcu and call_rcu + threads) should be released before a fork() is performed, except for the + rather common scenario where fork() is immediately followed by exec() in + the child process. The only implementation not subject to that rule is + liburcu-bp, which is designed to handle fork() by calling + rcu_bp_before_fork, rcu_bp_after_fork_parent and + rcu_bp_after_fork_child. + + Applications that use call_rcu() and that fork() without + doing an immediate exec() must take special action. The parent + must invoke call_rcu_before_fork() before the fork() and + call_rcu_after_fork_parent() after the fork(). The child + process must invoke call_rcu_after_fork_child(). + These three APIs are suitable for passing to pthread_atfork().