linux-kernel - Re: [PATCH 14/32] nohz/cpuset: Don't turn off the tick if rcu needs it

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Date:	Mon, 29 Aug 2011 17:36:31 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [PATCH 14/32] nohz/cpuset: Don't turn off the tick if rcu needs
 it

On Mon, 2011-08-15 at 17:52 +0200, Frederic Weisbecker wrote:
> @@ -2446,6 +2447,19 @@ bool cpuset_nohz_can_stop_tick(void)
>         if (rq->nr_running > 1)
>                 return false;
>  
> +       cpu = smp_processor_id();
> +
> +       /*
> +        * FIXME: will probably be removed soon as it's
> +        * already checked from tick_nohz_stop_sched_tick()
> +        */
> +       if (rcu_needs_cpu(cpu))
> +               return false;
> +
> +       /* Is there a grace period to complete ? */
> +       if (rcu_pending(cpu))
> +               return false;
> +
>         return true;
>  } 

This really shouldn't live in sched.c, also I would have expected
tick_nohz_can_stop_tick() to do this, its named like it does this.
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