On Tue, Sep 18, 2012 at 05:12:16PM +0800, Lai Jiangshan wrote:
> On 08/31/2012 02:45 AM, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <[email protected]>
> >
> > 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 <[email protected]>
>
> Good. (Sorry, I'm late.)
But, as it turns out, not too late. ;-)
Thank you for the review!
Thanx, Paul
> Reviewed-by: Lai Jiangshan <[email protected]>
>
> > ---
> > 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 [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
