X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=Documentation%2FRCU%2Frcu.txt;h=2a23523ce4712d2b972a0d99ea22fcf00912ab8c;hb=6b3ef48adf847f7adf11c870e3ffacac150f1564;hp=6fa092251586e14930c6d51d8bde1d4566512138;hpb=dd81eca83c8300c95d8a1eaf0d38f56513711535;p=safe%2Fjmp%2Flinux-2.6

diff --git a/Documentation/RCU/rcu.txt b/Documentation/RCU/rcu.txt
index 6fa0922..2a23523 100644
--- 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_TREE_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?
 
@@ -45,7 +53,11 @@ 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",
-	"synchronize_rcu", and "synchronize_net".
+	"srcu_read_lock", "srcu_read_unlock", "synchronize_rcu",
+	"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?
 
@@ -66,7 +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_TREE_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?
 
@@ -111,6 +127,11 @@ o	What are all these files in this directory?
 
 		You are reading it!
 
+	rcuref.txt
+
+		Describes how to combine use of reference counts
+		with RCU.
+
 	whatisRCU.txt
 
 		Overview of how the RCU implementation works.  Along