path: root/Documentation/RCU/rcu.txt
diff options
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2008-01-25 21:08:25 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-25 21:08:25 +0100
commitf85d6c7168887e6659f4d00fa5f34fa23dbde1bb (patch)
tree8a06a394c5963fe1428d023e03ac9896087b23b2 /Documentation/RCU/rcu.txt
parenteaf649e9fe6685f4c5a392cd0e16df5fd6660b7c (diff)
Preempt-RCU: update RCU Documentation.
This patch updates the RCU documentation to reflect preemptible RCU as well as recent publications. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> Reviewed-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'Documentation/RCU/rcu.txt')
1 files changed, 17 insertions, 2 deletions
diff --git a/Documentation/RCU/rcu.txt b/Documentation/RCU/rcu.txt
index f84407cba816..95821a29ae41 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_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?