add missing comment to wfstack.c

[urcu.git] / README

diff --git a/README b/README
index ba9c16dbdd5f6dfb8f7b96ad719eafda11b8a02f..796b9cfcd4dbad1d87775b22e53559dcdf7df7ed 100644 (file)
--- a/README
+++ b/README
@@ -25,8 +25,22 @@ 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.
+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
 -----------------
@@ -44,19 +58,11 @@ Usage of liburcu
 
        * #include <urcu.h>
        * 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 -DSIGRCU by modifying Makefile.build.inc.
-
-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 does not need to
-         reserve a signal number. RCU_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
 
@@ -68,6 +74,23 @@ 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 <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>
@@ -138,6 +161,14 @@ 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