-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
+and Sparcv9 32/64 are supported. Only tested on Linux so far, but should
+theoretically work on other operating systems.
+
+Alpha and ia64 architectures are supported, but depend on 4.x gcc with atomic
+builtins support.
+
+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
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 <urcu.h>
+ * 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 <urcu-qsbr.h>
+ * 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 <urcu.h>
+ * 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 <urcu.h>
+ * 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 <urcu-bp.h>
+ * 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
After, synchronize_rcu() must be called. When it returns, the old
values are not in usage anymore.
+Usage of liburcu-defer
+
+ * #include <urcu-defer.h>
+ * 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.
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.
projects / urcu.git / blobdiff