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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-01-23 22:35:45 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-03-04 08:05:25 -0800
commitfea651267e52a88e7b81e01b6717d968254b6ddb (patch)
treee8dd6001a6c6aba5d747fe7fdee5b91fd13a4246 /Documentation/RCU
parent37743de384951ef97c040e69039820c987849501 (diff)
downloadlinux-fea651267e52a88e7b81e01b6717d968254b6ddb.tar.gz
rcu: add documentation saying which RCU flavor to choose
Reported-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/whatisRCU.txt31
1 files changed, 31 insertions, 0 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index cfaac34c455..6ef692667e2 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -849,6 +849,37 @@ All: lockdep-checked RCU-protected pointer access
See the comment headers in the source code (or the docbook generated
from them) for more information.
+However, given that there are no fewer than four families of RCU APIs
+in the Linux kernel, how do you choose which one to use? The following
+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
+ 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,
+ 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
+ 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
+ RCU, but inappropriate for other synchronization mechanisms?
+ If so, consider SLAB_DESTROY_BY_RCU. But please be careful!
+
+f. Otherwise, use RCU.
+
+Of course, this all assumes that you have determined that RCU is in fact
+the right tool for your job.
+
8. ANSWERS TO QUICK QUIZZES