linux-kernel - Re: [PATCH RFC tip/core/rcu 1/2] Eliminate redundant rcu_sysidle

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Message-ID: <20140724142911.GA25788@localhost.localdomain>
Date:	Thu, 24 Jul 2014 16:29:14 +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, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 1/2] Eliminate redundant
 rcu_sysidle_state variable

On Wed, Jul 23, 2014 at 09:28:52AM -0700, Paul E. McKenney wrote:
> Now that we have rcu_state_p, which references rcu_preempt_state for
> TREE_PREEMPT_RCU and rcu_sched_state for TREE_RCU, we don't need a
> separate rcu_sysidle_state variable.  This commit therefore eliminates
> rcu_preempt_state in favor of rcu_state_p.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Acked-by: Frederic Weisbecker <fweisbec@...il.com>

> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 24f5bd54ca9b..e31fa71c4d3a 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2662,16 +2662,6 @@ static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
>  
>  #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
>  
> -/*
> - * Define RCU flavor that holds sysidle state.  This needs to be the
> - * most active flavor of RCU.
> - */
> -#ifdef CONFIG_PREEMPT_RCU
> -static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
> -#else /* #ifdef CONFIG_PREEMPT_RCU */
> -static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
> -#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
> -
>  static int full_sysidle_state;		/* Current system-idle state. */
>  #define RCU_SYSIDLE_NOT		0	/* Some CPU is not idle. */
>  #define RCU_SYSIDLE_SHORT	1	/* All CPUs idle for brief period. */
> @@ -2813,7 +2803,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
>  	 * not the flavor of RCU that tracks sysidle state, or if this
>  	 * is an offline or the timekeeping CPU, nothing to do.
>  	 */
> -	if (!*isidle || rdp->rsp != rcu_sysidle_state ||
> +	if (!*isidle || rdp->rsp != rcu_state_p ||
>  	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
>  		return;
>  	if (rcu_gp_in_progress(rdp->rsp))
> @@ -2839,7 +2829,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
>   */
>  static bool is_sysidle_rcu_state(struct rcu_state *rsp)
>  {
> -	return rsp == rcu_sysidle_state;
> +	return rsp == rcu_state_p;
>  }
>  
>  /*
> @@ -2917,7 +2907,7 @@ static void rcu_sysidle_cancel(void)
>  static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
>  			       unsigned long maxj, bool gpkt)
>  {
> -	if (rsp != rcu_sysidle_state)
> +	if (rsp != rcu_state_p)
>  		return;  /* Wrong flavor, ignore. */
>  	if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
>  		return;  /* Running state machine from timekeeping CPU. */
> @@ -2986,13 +2976,12 @@ bool rcu_sys_is_idle(void)
>  
>  			/* Scan all the CPUs looking for nonidle CPUs. */
>  			for_each_possible_cpu(cpu) {
> -				rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
> +				rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
>  				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
>  				if (!isidle)
>  					break;
>  			}
> -			rcu_sysidle_report(rcu_sysidle_state,
> -					   isidle, maxj, false);
> +			rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
>  			oldrss = rss;
>  			rss = ACCESS_ONCE(full_sysidle_state);
>  		}
> @@ -3019,7 +3008,7 @@ bool rcu_sys_is_idle(void)
>  	 * provided by the memory allocator.
>  	 */
>  	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
> -	    !rcu_gp_in_progress(rcu_sysidle_state) &&
> +	    !rcu_gp_in_progress(rcu_state_p) &&
>  	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
>  		call_rcu(&rsh.rh, rcu_sysidle_cb);
>  	return false;
> 
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