update README

- Add comment about new threads and signals
- document DEBUG_RCU

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

diff --git a/README b/README
index ae8b6619cb5645dfcab48f3bf96d257b20b42973..0ec723dea10186d13e6c11705e18a0c8149ae288 100644 (file)
--- a/README
+++ b/README
@@ -39,11 +39,20 @@ Being careful with signals
        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().
+
 Usage of CONFIG_URCU_AVOID_SIGNALS
 
        CONFIG_URCU_AVOID_SIGNALS uses full SMP barriers for readers. This
        eliminates the need for signals but results in slower reads.
 
+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.
 
 Usage of DEBUG_YIELD