linux-kernel - Re: [PATCH tip/core/rcu 05/86] rcu: move TREE

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Message-ID: <20110506054657.GC2641@linux.vnet.ibm.com>
Date:	Thu, 5 May 2011 22:46:57 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 05/86] rcu: move TREE_RCU from softirq to
 kthread

On Thu, May 05, 2011 at 05:31:35PM +0800, Yong Zhang wrote:
> On Sun, May 1, 2011 at 9:20 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > From: Paul E. McKenney <paul.mckenney@...aro.org>
> >
> > If RCU priority boosting is to be meaningful, callback invocation must
> > be boosted in addition to preempted RCU readers.  Otherwise, in presence
> > of CPU real-time threads, the grace period ends, but the callbacks don't
> > get invoked.  If the callbacks don't get invoked, the associated memory
> > doesn't get freed, so the system is still subject to OOM.
> >
> > But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit
> > moves the callback invocations to a kthread, which can be boosted easily.
> >
> > Also add comments and properly synchronized all accesses to
> > rcu_cpu_kthread_task, as suggested by Lai Jiangshan.
> >
> > Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> [snip]
> > + * Drop to non-real-time priority and yield, but only after posting a
> > + * timer that will cause us to regain our real-time priority if we
> > + * remain preempted.  Either way, we restore our real-time priority
> > + * before returning.
> > + */
> > +static void rcu_yield(int cpu)
> > +{
> > +       struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
> > +       struct sched_param sp;
> > +       struct timer_list yield_timer;
> > +
> > +       setup_timer(&yield_timer, rcu_cpu_kthread_timer, (unsigned long)rdp);
> 
> setup_timer_on_stack() should be used here :)

Good eyes!!!  Fixed, will update the -rcu git tree.

							Thanx, Paul
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