linux-kernel - Re: [PATCH tip/core/rcu 06/24] rcu: Cleanup rcu_init

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Message-ID: <20150512232232.3f3b23c6@grimm.local.home>
Date:	Tue, 12 May 2015 23:22:32 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
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,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
	Alexander Gordeev <agordeev@...hat.com>
Subject: Re: [PATCH tip/core/rcu 06/24] rcu: Cleanup rcu_init_geometry()
 code and arithmetics

On Tue, 12 May 2015 15:30:36 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> @@ -4103,24 +4102,21 @@ static void __init rcu_init_geometry(void)
>  		return;
>  	}
>  
> +	/* Calculate the number of levels in the tree. */
> +	for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {

Should this start at i = 1 as it use to? Also, should there be a safety
check too:

	for (i = 1; i <= MAX_RCU_LVLS && nr_cpu_ids > rcu_capacity[i]; i++) {


> +	}
> +	rcu_num_lvls = i;
> +
>  	/* Calculate the number of rcu_nodes at each level of the tree. */
> -	for (i = 1; i <= MAX_RCU_LVLS; i++)
> -		if (nr_cpu_ids <= rcu_capacity[i]) {
> -			for (j = 0; j <= i; j++) {
> -				int cap = rcu_capacity[i - j];
> -				num_rcu_lvl[j] = DIV_ROUND_UP(nr_cpu_ids, cap);
> -			}
> -			rcu_num_lvls = i;
> -			for (j = i + 1; j <= MAX_RCU_LVLS; j++)
> -				num_rcu_lvl[j] = 0;
> -			break;
> -		}
> +	for (i = 0; i < rcu_num_lvls; i++) {

Hmm, up above we have: for (j = 0; j <= i; j++)

and now we have rcu_num_lvls = i, so shouldn't this be;

  for (i = 0; i <= rcu_num_lvls; i++)

?

-- Steve

> +		int cap = rcu_capacity[rcu_num_lvls - i];
> +		num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
> +	}
>  
>  	/* Calculate the total number of rcu_node structures. */
>  	rcu_num_nodes = 0;
> -	for (i = 0; i <= MAX_RCU_LVLS; i++)
> +	for (i = 0; i < rcu_num_lvls; i++)
>  		rcu_num_nodes += num_rcu_lvl[i];
> -	rcu_num_nodes -= nr_cpu_ids;
>  }
>  
>  void __init rcu_init(void)

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