linux-kernel - Re: [PATCH tip/core/rcu 07/23] rcu: Provide OOM handler to motivate lazy RCU callbacks

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Date:	Thu, 06 Sep 2012 09:52:53 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 07/23] rcu: Provide OOM handler to motivate
 lazy RCU callbacks

On Thu, 2012-09-06 at 15:46 +0200, Peter Zijlstra wrote:
> On Thu, 2012-08-30 at 11:18 -0700, Paul E. McKenney wrote:
> > +       get_online_cpus();
> > +       for_each_online_cpu(cpu)
> > +               for_each_rcu_flavor(rsp)
> > +                       smp_call_function_single(cpu, rcu_oom_notify_cpu,
> > +                                                rsp, 1);
> > +       put_online_cpus(); 
> 
> I guess blasting IPIs around is better than OOM but still.. do you
> really need to wait for each cpu individually, or would a construct
> using on_each_cpu() be possible, or better yet, on_each_cpu_cond()?

Also, what about having the rcu_oom_notify_cpu handler do the
for_each_rcu_flavor() and not send an IPI multiple times to a single
CPU?

-- Steve


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