Merge branch 'for-linus' of git://git.monstr.eu/linux-2.6-microblaze

[pandora-kernel.git] / Documentation / RCU / rcu.txt

diff --git a/Documentation/RCU/rcu.txt b/Documentation/RCU/rcu.txt
index f84407c..7aa2002 100644 (file)
--- a/Documentation/RCU/rcu.txt
+++ b/Documentation/RCU/rcu.txt
@@ -36,6 +36,14 @@ o    How can the updater tell when a grace period has completed
        executed in user mode, or executed in the idle loop, we can
        safely free up that item.
 
+       Preemptible variants of RCU (CONFIG_PREEMPT_RCU) get the
+       same effect, but require that the readers manipulate CPU-local
+       counters.  These counters allow limited types of blocking
+       within RCU read-side critical sections.  SRCU also uses
+       CPU-local counters, and permits general blocking within
+       RCU read-side critical sections.  These two variants of
+       RCU detect grace periods by sampling these counters.
+
 o      If I am running on a uniprocessor kernel, which can only do one
        thing at a time, why should I wait for a grace period?
 
@@ -46,7 +54,10 @@ o    How can I see where RCU is currently used in the Linux kernel?
        Search for "rcu_read_lock", "rcu_read_unlock", "call_rcu",
        "rcu_read_lock_bh", "rcu_read_unlock_bh", "call_rcu_bh",
        "srcu_read_lock", "srcu_read_unlock", "synchronize_rcu",
-       "synchronize_net", and "synchronize_srcu".
+       "synchronize_net", "synchronize_srcu", and the other RCU
+       primitives.  Or grab one of the cscope databases from:
+
+       http://www.rdrop.com/users/paulmck/RCU/linuxusage/rculocktab.html
 
 o      What guidelines should I follow when writing code that uses RCU?
 
@@ -67,7 +78,11 @@ o    I hear that RCU is patented?  What is with that?
 
 o      I hear that RCU needs work in order to support realtime kernels?
 
-       Yes, work in progress.
+       This work is largely completed.  Realtime-friendly RCU can be
+       enabled via the CONFIG_PREEMPT_RCU kernel configuration parameter.
+       However, work is in progress for enabling priority boosting of
+       preempted RCU read-side critical sections.  This is needed if you
+       have CPU-bound realtime threads.
 
 o      Where can I find more information on RCU?