On 08/31/2012 02:45 AM, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> > > 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 <paul...@linux.vnet.ibm.com>
Good. (Sorry, I'm late.) Reviewed-by: Lai Jiangshan <la...@cn.fujitsu.com> > --- > Documentation/RCU/checklist.txt | 6 ++++++ > Documentation/RCU/whatisRCU.txt | 9 +++++++-- > 2 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt > index fc103d7..cdb20d4 100644 > --- a/Documentation/RCU/checklist.txt > +++ b/Documentation/RCU/checklist.txt > @@ -310,6 +310,12 @@ over a rather long period of time, but improvements are > always welcome! > code under the influence of preempt_disable(), you instead > need to use synchronize_irq() or synchronize_sched(). > > + This same limitation also applies to synchronize_rcu_bh() > + and synchronize_srcu(), as well as to the asynchronous and > + expedited forms of the three primitives, namely call_rcu(), > + call_rcu_bh(), call_srcu(), synchronize_rcu_expedited(), > + synchronize_rcu_bh_expedited(), and synchronize_srcu_expedited(). > + > 12. Any lock acquired by an RCU callback must be acquired elsewhere > with softirq disabled, e.g., via spin_lock_irqsave(), > spin_lock_bh(), etc. Failing to disable irq on a given > diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt > index 69ee188..bf0f6de 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
