linux-kernel - Re: [PATCH tip/core/rcu 05/17] rcu: remove redundant ACCESS_ONCE() from tick_do_timer

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Message-ID: <20140708144653.GE6571@localhost.localdomain>
Date:	Tue, 8 Jul 2014 16:46:55 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, dvhart@...ux.intel.com, oleg@...hat.com,
	sbw@....edu
Subject: Re: [PATCH tip/core/rcu 05/17] rcu: remove redundant ACCESS_ONCE()
 from tick_do_timer_cpu

On Mon, Jul 07, 2014 at 03:38:09PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> In kernels built with CONFIG_NO_HZ_FULL, tick_do_timer_cpu is constant
> once boot completes.  Thus, there is no need to wrap it in ACCESS_ONCE()
> in code that is built only when CONFIG_NO_HZ_FULL.  This commit therefore
> removes the redundant ACCESS_ONCE().
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

ACK, thanks!

> ---
>  kernel/rcu/tree_plugin.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 02ac0fb186b8..5da9f9b3abc9 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2844,7 +2844,7 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
>  static void rcu_bind_gp_kthread(void)
>  {
>  #ifdef CONFIG_NO_HZ_FULL
> -	int cpu = ACCESS_ONCE(tick_do_timer_cpu);
> +	int cpu = tick_do_timer_cpu;
>  
>  	if (cpu < 0 || cpu >= nr_cpu_ids)
>  		return;
> -- 
> 1.8.1.5
> 
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