path: root/Documentation/RCU/whatisRCU.txt
diff options
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-08-03 16:41:23 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-09-23 07:42:23 -0700
commit2aef619c7524d73d18ff7b102a1706066b69141d (patch)
treeda1409acbdc4baca4858af9fbc7e413fd5efa0d0 /Documentation/RCU/whatisRCU.txt
parent13dbf9140c726c307a9c7e2b7ff83cf95da3bb44 (diff)
rcu: Document SRCU dead-CPU capabilities, emphasize read-side limits
The current documentation did not help someone grepping for SRCU to learn that disabling preemption is not a replacement for srcu_read_lock(), so upgrade the documentation to bring this out, not just for SRCU, but also for RCU-bh. Also document the fact that SRCU readers are respected on CPUs executing in user mode, idle CPUs, and even on offline CPUs. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Diffstat (limited to 'Documentation/RCU/whatisRCU.txt')
1 files changed, 7 insertions, 2 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 69ee188515e7..bf0f6de2aa00 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -873,7 +873,7 @@ d. Do you need to treat NMI handlers, hardirq handlers,
and code segments with preemption disabled (whether
via preempt_disable(), local_irq_save(), local_bh_disable(),
or some other mechanism) as if they were explicit RCU readers?
- If so, you need RCU-sched.
+ If so, RCU-sched is the only choice that will work for you.
e. Do you need RCU grace periods to complete even in the face
of softirq monopolization of one or more of the CPUs? For
@@ -884,7 +884,12 @@ f. Is your workload too update-intensive for normal use of
RCU, but inappropriate for other synchronization mechanisms?
If so, consider SLAB_DESTROY_BY_RCU. But please be careful!
-g. Otherwise, use RCU.
+g. Do you need read-side critical sections that are respected
+ even though they are in the middle of the idle loop, during
+ user-mode execution, or on an offlined CPU? If so, SRCU is the
+ only choice that will work for you.
+h. Otherwise, use RCU.
Of course, this all assumes that you have determined that RCU is in fact
the right tool for your job.