From: Josh Triplett <josh@joshtriplett.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com,
fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org
Subject: Re: [PATCH tip/core/rcu 3/5] rcu: Document SRCU dead-CPU capabilities, emphasize read-side limits
Date: Thu, 30 Aug 2012 12:01:46 -0700 [thread overview]
Message-ID: <20120830190146.GD6749@jtriplet-mobl1> (raw)
In-Reply-To: <1346352312-31987-3-git-send-email-paulmck@linux.vnet.ibm.com>
On Thu, Aug 30, 2012 at 11:45:10AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@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 <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> 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.
> --
> 1.7.8
>
next prev parent reply other threads:[~2012-08-30 19:01 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-30 18:44 [PATCH tip/core/rcu 0/5] Documentation and rcutorture changes Paul E. McKenney
2012-08-30 18:45 ` [PATCH tip/core/rcu 1/5] rcu: Update rcutorture defaults Paul E. McKenney
2012-08-30 18:45 ` [PATCH tip/core/rcu 2/5] rcu: Track CPU-hotplug duration statistics Paul E. McKenney
2012-08-30 19:00 ` Josh Triplett
2012-08-30 20:38 ` Paul E. McKenney
2012-08-30 23:23 ` Josh Triplett
2012-08-30 18:45 ` [PATCH tip/core/rcu 3/5] rcu: Document SRCU dead-CPU capabilities, emphasize read-side limits Paul E. McKenney
2012-08-30 19:01 ` Josh Triplett [this message]
2012-09-18 9:12 ` Lai Jiangshan
2012-09-18 23:32 ` Paul E. McKenney
2012-08-30 18:45 ` [PATCH tip/core/rcu 4/5] rcu: Switch rcutorture to pr_alert() and friends Paul E. McKenney
2012-08-30 19:05 ` Josh Triplett
2012-08-30 18:45 ` [PATCH tip/core/rcu 5/5] rcu: Prevent initialization race in rcutorture kthreads Paul E. McKenney
2012-08-30 19:15 ` Josh Triplett
2012-08-30 18:57 ` [PATCH tip/core/rcu 1/5] rcu: Update rcutorture defaults Josh Triplett
2012-08-30 21:35 ` Paul E. McKenney
2012-08-30 23:24 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 0/5] Documentation and rcutorture changes Josh Triplett
2012-08-30 21:46 ` Paul E. McKenney
2012-08-30 23:22 ` Josh Triplett
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