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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
> 

  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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