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,
"Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: [PATCH tip/core/rcu 05/15] rcu: Improve boost selection when moving tasks to root rcu_node
Date: Fri, 31 Aug 2012 11:09:12 -0700 [thread overview]
Message-ID: <20120831180912.GC4259@jtriplet-mobl1> (raw)
In-Reply-To: <1346352988-32444-5-git-send-email-paulmck@linux.vnet.ibm.com>
On Thu, Aug 30, 2012 at 11:56:18AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@linaro.org>
>
> The rcu_preempt_offline_tasks() moves all tasks queued on a given leaf
> rcu_node structure to the root rcu_node, which is done when the last CPU
> corresponding the the leaf rcu_node structure goes offline. Now that
> RCU-preempt's synchronize_rcu_expedited() implementation blocks CPU-hotplug
> operations during the initialization of each rcu_node structure's
> ->boost_tasks pointer, rcu_preempt_offline_tasks() can do a better job
> of setting the root rcu_node's ->boost_tasks pointer.
>
> The key point is that rcu_preempt_offline_tasks() runs as part of the
> CPU-hotplug process, so that a concurrent synchronize_rcu_expedited() is
> guaranteed to either have not started on the one hand (in which case there
> is no boosting on behalf of the expedited grace period) to be completely
Missing word: s/to be/or to be/
> initialized on the other (in which case, in absence of other priority
s/absence/the absence/
> boosting, all ->boost_tasks pointers will be initialized). Therefore,
> if rcu_preempt_offline_tasks() finds that the ->boost_tasks pointer is
> equal to the ->exp_tasks pointer, it can be sure that it is correcty
> placed.
>
> The case where there was boosting ongoing at the time that the
s/The/In the/
> synchronize_rcu_expedited() function started, different nodes might
> start boosting the tasks blocking the expedited grace period at different
> times. In this mixed case, the root node will either be boosting tasks
> for the expedited grace period already, or it will start as soon as it
> gets done boosting for the normal grace period -- but in this latter
> case, the root node's tasks needed to be boosted in any case.
>
> This commit therefore adds a check of the ->boost_tasks pointer against
> the ->exp_tasks pointer to the list that prevents updating ->boost_tasks.
Seems like some hint of this explanation really ought to end up in a
comment somewhere...
> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> ---
> kernel/rcutree_plugin.h | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> index b1b4851..c930a47 100644
> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -591,7 +591,8 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
> /* In case root is being boosted and leaf was not. */
> raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
> if (rnp_root->boost_tasks != NULL &&
> - rnp_root->boost_tasks != rnp_root->gp_tasks)
> + rnp_root->boost_tasks != rnp_root->gp_tasks &&
> + rnp_root->boost_tasks != rnp_root->exp_tasks)
> rnp_root->boost_tasks = rnp_root->gp_tasks;
> raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
> #endif /* #ifdef CONFIG_RCU_BOOST */
> --
> 1.7.8
>
next prev parent reply other threads:[~2012-08-31 18:09 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-30 18:56 [PATCH tip/core/rcu 0/15] Miscellaneous fixes Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 02/15] rcu: Pull TINY_RCU dyntick-idle tracing into non-idle region Paul E. McKenney
2012-08-31 16:53 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 03/15] rcu: Properly initialize ->boost_tasks on CPU offline Paul E. McKenney
2012-08-31 17:56 ` Josh Triplett
2012-09-06 14:40 ` Peter Zijlstra
2012-09-06 20:58 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-31 18:00 ` Josh Triplett
2012-09-04 22:33 ` Paul E. McKenney
2012-09-04 22:48 ` Josh Triplett
2012-09-04 22:51 ` Steven Rostedt
2012-09-04 23:08 ` Josh Triplett
2012-09-04 23:23 ` Steven Rostedt
2012-09-04 23:33 ` Josh Triplett
2012-09-04 23:43 ` Paul E. McKenney
2012-09-06 18:54 ` Josh Triplett
2012-09-06 19:54 ` Steven Rostedt
2012-09-07 6:09 ` Josh Triplett
2012-09-07 14:24 ` Paul E. McKenney
2012-09-07 14:47 ` Josh Triplett
2012-09-07 15:16 ` Steven Rostedt
2012-09-12 1:07 ` Paul E. McKenney
2012-09-12 14:13 ` Steven Rostedt
2012-09-12 15:03 ` Paul E. McKenney
2012-09-12 15:18 ` Steven Rostedt
2012-09-12 16:57 ` Paul E. McKenney
2012-09-04 23:46 ` Steven Rostedt
2012-09-05 0:42 ` Josh Triplett
2012-09-05 6:23 ` [PATCH] trace: Don't declare trace_*_rcuidle functions in modules Josh Triplett
2012-09-05 14:26 ` Mathieu Desnoyers
2012-09-05 16:36 ` Paul E. McKenney
2012-09-06 19:49 ` Steven Rostedt
2012-09-14 6:07 ` [tip:core/rcu] trace: Don' t " tip-bot for Josh Triplett
2012-09-04 23:14 ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 05/15] rcu: Improve boost selection when moving tasks to root rcu_node Paul E. McKenney
2012-08-31 18:09 ` Josh Triplett [this message]
2012-08-30 18:56 ` [PATCH tip/core/rcu 06/15] rcu: Make offline-CPU checking allow for indefinite delays Paul E. McKenney
2012-08-31 18:12 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 07/15] rcu: Fix obsolete rcu_initiate_boost() header comment Paul E. McKenney
2012-08-31 18:13 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 08/15] rcu: Apply for_each_rcu_flavor() to increment_cpu_stall_ticks() Paul E. McKenney
2012-08-31 18:15 ` Josh Triplett
2012-09-04 22:44 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 09/15] rcu: Avoid rcu_print_detail_task_stall_rnp() segfault Paul E. McKenney
2012-08-31 18:19 ` Josh Triplett
2012-09-04 22:46 ` Paul E. McKenney
2012-09-04 22:55 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings Paul E. McKenney
2012-08-31 18:23 ` Josh Triplett
2012-09-04 22:51 ` Paul E. McKenney
2012-09-06 14:51 ` Peter Zijlstra
2012-09-06 21:01 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU " Paul E. McKenney
2012-08-31 18:24 ` Josh Triplett
2012-09-06 14:56 ` Peter Zijlstra
2012-09-06 15:07 ` Steven Rostedt
2012-09-06 15:19 ` Peter Zijlstra
2012-09-06 21:03 ` Paul E. McKenney
2012-09-06 21:41 ` Steven Rostedt
2012-09-06 21:58 ` Paul E. McKenney
2012-09-06 22:05 ` Steven Rostedt
2012-09-06 22:22 ` Paul E. McKenney
2012-09-07 7:00 ` Peter Zijlstra
2012-09-07 14:42 ` Steven Rostedt
2012-08-30 18:56 ` [PATCH tip/core/rcu 12/15] rcu: Remove redundant memory barrier from __call_rcu() Paul E. McKenney
2012-08-31 18:30 ` Josh Triplett
2012-08-31 18:40 ` Josh Triplett
2012-08-30 18:56 ` [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save() Paul E. McKenney
2012-08-31 18:34 ` Josh Triplett
2012-09-04 23:03 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 14/15] time: RCU permitted to stop idle entry via softirq Paul E. McKenney
2012-08-31 18:51 ` Josh Triplett
2012-09-06 15:12 ` Peter Zijlstra
2012-09-06 21:35 ` Paul E. McKenney
2012-09-06 21:57 ` Steven Rostedt
2012-09-06 22:11 ` Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 15/15] kmemleak: Replace list_for_each_continue_rcu with new interface Paul E. McKenney
2012-08-31 18:55 ` Josh Triplett
2012-09-04 23:41 ` Paul E. McKenney
2012-08-31 16:49 ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Josh Triplett
2012-09-04 22:36 ` Paul E. McKenney
2012-09-06 14:38 ` Peter Zijlstra
2012-09-06 20:51 ` Paul E. McKenney
2012-09-07 6:54 ` Peter Zijlstra
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