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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
Subject: Re: [PATCH tip/core/rcu 02/23] rcu: Allow RCU grace-period initialization to be preempted
Date: Sat, 1 Sep 2012 18:09:35 -0700	[thread overview]
Message-ID: <20120902010935.GB5713@leaf> (raw)
In-Reply-To: <1346350718-30937-2-git-send-email-paulmck@linux.vnet.ibm.com>

On Thu, Aug 30, 2012 at 11:18:17AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> RCU grace-period initialization is currently carried out with interrupts
> disabled, which can result in 200-microsecond latency spikes on systems
> on which RCU has been configured for 4096 CPUs.  This patch therefore
> makes the RCU grace-period initialization be preemptible, which should
> eliminate those latency spikes.  Similar spikes from grace-period cleanup
> and the forcing of quiescent states will be dealt with similarly by later
> patches.
> 
> Reported-by: Mike Galbraith <mgalbraith@suse.de>
> Reported-by: Dimitri Sivanich <sivanich@sgi.com>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Does it make sense to have cond_resched() right before the continues,
which lead right back up to the wait_event_interruptible at the top of
the loop?  Or do you expect to usually find that event already
signalled?

In any case:

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  kernel/rcutree.c |   17 ++++++++++-------
>  1 files changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index e1c5868..ef56aa3 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1069,6 +1069,7 @@ static int rcu_gp_kthread(void *arg)
>  			 * don't start another one.
>  			 */
>  			raw_spin_unlock_irqrestore(&rnp->lock, flags);
> +			cond_resched();
>  			continue;
>  		}
>  
> @@ -1079,6 +1080,7 @@ static int rcu_gp_kthread(void *arg)
>  			 */
>  			rsp->fqs_need_gp = 1;
>  			raw_spin_unlock_irqrestore(&rnp->lock, flags);
> +			cond_resched();
>  			continue;
>  		}
>  
> @@ -1089,10 +1091,10 @@ static int rcu_gp_kthread(void *arg)
>  		rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */
>  		rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
>  		record_gp_stall_check_time(rsp);
> -		raw_spin_unlock(&rnp->lock);  /* leave irqs disabled. */
> +		raw_spin_unlock_irqrestore(&rnp->lock, flags);
>  
>  		/* Exclude any concurrent CPU-hotplug operations. */
> -		raw_spin_lock(&rsp->onofflock);  /* irqs already disabled. */
> +		get_online_cpus();
>  
>  		/*
>  		 * Set the quiescent-state-needed bits in all the rcu_node
> @@ -1112,7 +1114,7 @@ static int rcu_gp_kthread(void *arg)
>  		 * due to the fact that we have irqs disabled.
>  		 */
>  		rcu_for_each_node_breadth_first(rsp, rnp) {
> -			raw_spin_lock(&rnp->lock); /* irqs already disabled. */
> +			raw_spin_lock_irqsave(&rnp->lock, flags);
>  			rcu_preempt_check_blocked_tasks(rnp);
>  			rnp->qsmask = rnp->qsmaskinit;
>  			rnp->gpnum = rsp->gpnum;
> @@ -1123,15 +1125,16 @@ static int rcu_gp_kthread(void *arg)
>  			trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
>  						    rnp->level, rnp->grplo,
>  						    rnp->grphi, rnp->qsmask);
> -			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
> +			raw_spin_unlock_irqrestore(&rnp->lock, flags);
> +			cond_resched();
>  		}
>  
>  		rnp = rcu_get_root(rsp);
> -		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
> +		raw_spin_lock_irqsave(&rnp->lock, flags);
>  		/* force_quiescent_state() now OK. */
>  		rsp->fqs_state = RCU_SIGNAL_INIT;
> -		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
> -		raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
> +		raw_spin_unlock_irqrestore(&rnp->lock, flags);
> +		put_online_cpus();
>  	}
>  	return 0;
>  }
> -- 
> 1.7.8
> 

  reply	other threads:[~2012-09-02  1:09 UTC|newest]

Thread overview: 85+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-30 18:18 [PATCH tip/core/rcu 0/23] Improvements to RT response on big systems and expedited functions Paul E. McKenney
2012-08-30 18:18 ` [PATCH tip/core/rcu 01/23] rcu: Move RCU grace-period initialization into a kthread Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 02/23] rcu: Allow RCU grace-period initialization to be preempted Paul E. McKenney
2012-09-02  1:09     ` Josh Triplett [this message]
2012-09-05  1:22       ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 03/23] rcu: Move RCU grace-period cleanup into kthread Paul E. McKenney
2012-09-02  1:22     ` Josh Triplett
2012-09-06 13:34     ` Peter Zijlstra
2012-09-06 17:29       ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 04/23] rcu: Allow RCU grace-period cleanup to be preempted Paul E. McKenney
2012-09-02  1:36     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 05/23] rcu: Prevent offline CPUs from executing RCU core code Paul E. McKenney
2012-09-02  1:45     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 06/23] rcu: Break up rcu_gp_kthread() into subfunctions Paul E. McKenney
2012-09-02  2:11     ` Josh Triplett
2012-09-06 13:39     ` Peter Zijlstra
2012-09-06 17:32       ` Paul E. McKenney
2012-09-06 18:49         ` Josh Triplett
2012-09-06 19:09           ` Peter Zijlstra
2012-09-06 20:30             ` Paul E. McKenney
2012-09-06 20:30           ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 07/23] rcu: Provide OOM handler to motivate lazy RCU callbacks Paul E. McKenney
2012-09-02  2:13     ` Josh Triplett
2012-09-03  9:08     ` Lai Jiangshan
2012-09-05 17:45       ` Paul E. McKenney
2012-09-06 13:46     ` Peter Zijlstra
2012-09-06 13:52       ` Steven Rostedt
2012-09-06 17:41         ` Paul E. McKenney
2012-09-06 17:46           ` Peter Zijlstra
2012-09-06 20:32             ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 08/23] rcu: Segregate rcu_state fields to improve cache locality Paul E. McKenney
2012-09-02  2:51     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 09/23] rcu: Move quiescent-state forcing into kthread Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 10/23] rcu: Allow RCU quiescent-state forcing to be preempted Paul E. McKenney
2012-09-02  5:23     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 11/23] rcu: Adjust debugfs tracing for kthread-based quiescent-state forcing Paul E. McKenney
2012-09-02  6:05     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 12/23] rcu: Prevent force_quiescent_state() memory contention Paul E. McKenney
2012-09-02 10:47     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 13/23] rcu: Control grace-period duration from sysfs Paul E. McKenney
2012-09-03  9:30     ` Josh Triplett
2012-09-03  9:31       ` Josh Triplett
2012-09-06 14:15     ` Peter Zijlstra
2012-09-06 17:53       ` Paul E. McKenney
2012-09-06 18:28         ` Peter Zijlstra
2012-09-06 20:37           ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 14/23] rcu: Remove now-unused rcu_state fields Paul E. McKenney
2012-09-03  9:31     ` Josh Triplett
2012-09-06 14:17     ` Peter Zijlstra
2012-09-06 18:02       ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 15/23] rcu: Make rcutree module parameters visible in sysfs Paul E. McKenney
2012-09-03  9:32     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 16/23] rcu: Prevent initialization-time quiescent-state race Paul E. McKenney
2012-09-03  9:37     ` Josh Triplett
2012-09-05 18:19       ` Paul E. McKenney
2012-09-05 18:55         ` Josh Triplett
2012-09-05 19:49           ` Paul E. McKenney
2012-09-06 14:21         ` Peter Zijlstra
2012-09-06 16:18           ` Paul E. McKenney
2012-09-06 16:22             ` Peter Zijlstra
2012-08-30 18:18   ` [PATCH tip/core/rcu 17/23] rcu: Fix day-zero grace-period initialization/cleanup race Paul E. McKenney
2012-09-03  9:39     ` Josh Triplett
2012-09-06 14:24     ` Peter Zijlstra
2012-09-06 18:06       ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 18/23] rcu: Add random PROVE_RCU_DELAY to grace-period initialization Paul E. McKenney
2012-09-03  9:41     ` Josh Triplett
2012-09-06 14:27     ` Peter Zijlstra
2012-09-06 18:25       ` Paul E. McKenney
2012-08-30 18:18   ` [PATCH tip/core/rcu 19/23] rcu: Adjust for unconditional ->completed assignment Paul E. McKenney
2012-09-03  9:42     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 20/23] rcu: Remove callback acceleration from grace-period initialization Paul E. McKenney
2012-09-03  9:42     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 21/23] rcu: Eliminate signed overflow in synchronize_rcu_expedited() Paul E. McKenney
2012-09-03  9:43     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 22/23] rcu: Reduce synchronize_rcu_expedited() latency Paul E. McKenney
2012-09-03  9:46     ` Josh Triplett
2012-08-30 18:18   ` [PATCH tip/core/rcu 23/23] rcu: Simplify quiescent-state detection Paul E. McKenney
2012-09-03  9:56     ` Josh Triplett
2012-09-06 14:36     ` Peter Zijlstra
2012-09-06 20:01       ` Paul E. McKenney
2012-09-06 21:18         ` Mathieu Desnoyers
2012-09-06 21:31           ` Paul E. McKenney
2012-09-02  1:04   ` [PATCH tip/core/rcu 01/23] rcu: Move RCU grace-period initialization into a kthread Josh Triplett
2012-09-06 13:32   ` Peter Zijlstra
2012-09-06 17:00     ` Paul E. McKenney

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