Commit-ID: fea651267e52a88e7b81e01b6717d968254b6ddb Gitweb: http://git.kernel.org/tip/fea651267e52a88e7b81e01b6717d968254b6ddb Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Sun, 23 Jan 2011 22:35:45 -0800 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Fri, 4 Mar 2011 08:05:25 -0800 rcu: add documentation saying which RCU flavor to choose Reported-by: Paul Mackerras <paulus@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- Documentation/RCU/whatisRCU.txt | 31 +++++++++++++++++++++++++++++++ 1 files changed, 31 insertions(+), 0 deletions(-) diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index cfaac34..6ef6926 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 -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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