linux-kernel - Re: [PATCH, RFC] v4 scalable classic RCU implementation

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Date:	Sat, 06 Sep 2008 18:37:38 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	mingo@...e.hu, akpm@...ux-foundation.org, dipankar@...ibm.com,
	josht@...ux.vnet.ibm.com, schamp@....com, niv@...ibm.com,
	dvhltc@...ibm.com, ego@...ibm.com, laijs@...fujitsu.com,
	rostedt@...dmis.org, peterz@...radead.org, penberg@...helsinki.fi,
	andi@...stfloor.org
Subject: Re: [PATCH, RFC] v4 scalable classic RCU implementation

Hi Paul,

Paul E. McKenney wrote:
> o	The rcu_pending() and rcu_needs_cpu() primitives are now
> 	much more aggressive about permitting CPUs to enter dynticks
> 	idle mode.  Only CPUs that have RCU callbacks are kept out
> 	of dynticks idle mode.
>   

I've noticed that right now rcu_enter_nohz() can be nested within 
rcu_irq_enter():
irq_exit() first calls tick_nohz_stop_sched_tick(), then rcu_irq_exit().
And tick_nohz_stop_sched_tick() can switch into nohz mode.

Is that intentional? Does rcupreempt support that? It broke my rcustate 
code on x86-64.

I would prefer if something like the attached patch is applied. What do 
you think?
Do you need the patch as well?

--
    Manfred

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