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-rw-r--r--Documentation/RCU/whatisRCU.txt19
1 files changed, 14 insertions, 5 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 6ef692667e2..6bbe8dcdc3d 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -4,6 +4,7 @@ to start learning about RCU:
1. What is RCU, Fundamentally? http://lwn.net/Articles/262464/
2. What is RCU? Part 2: Usage http://lwn.net/Articles/263130/
3. RCU part 3: the RCU API http://lwn.net/Articles/264090/
+4. The RCU API, 2010 Edition http://lwn.net/Articles/418853/
What is RCU?
@@ -834,6 +835,8 @@ SRCU: Critical sections Grace period Barrier
srcu_read_lock synchronize_srcu N/A
srcu_read_unlock synchronize_srcu_expedited
+ srcu_read_lock_raw
+ srcu_read_unlock_raw
srcu_dereference
SRCU: Initialization/cleanup
@@ -855,27 +858,33 @@ list can be helpful:
a. Will readers need to block? If so, you need SRCU.
-b. What about the -rt patchset? If readers would need to block
+b. Is it necessary to start a read-side critical section in a
+ hardirq handler or exception handler, and then to complete
+ this read-side critical section in the task that was
+ interrupted? If so, you need SRCU's srcu_read_lock_raw() and
+ srcu_read_unlock_raw() primitives.
+
+c. What about the -rt patchset? If readers would need to block
in an non-rt kernel, you need SRCU. If readers would block
in a -rt kernel, but not in a non-rt kernel, SRCU is not
necessary.
-c. Do you need to treat NMI handlers, hardirq handlers,
+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.
-d. Do you need RCU grace periods to complete even in the face
+e. Do you need RCU grace periods to complete even in the face
of softirq monopolization of one or more of the CPUs? For
example, is your code subject to network-based denial-of-service
attacks? If so, you need RCU-bh.
-e. Is your workload too update-intensive for normal use of
+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!
-f. Otherwise, use RCU.
+g. Otherwise, use RCU.
Of course, this all assumes that you have determined that RCU is in fact
the right tool for your job.