# [PATCH tip/core/rcu 06/24] rcu: Cleanup rcu_init_geometry() code and arithmetics

From: Paul E. McKenney
Date: Tue May 12 2015 - 18:32:14 EST

From: Alexander Gordeev <agordeev@xxxxxxxxxx>

This update simplifies rcu_init_geometry() code flow
and makes calculation of the total number of rcu_node

The update relies on the fact num_rcu_lvl[] is never
accessed beyond rcu_num_lvls index by the rest of the
code. Therefore, there is no need initialize the whole
num_rcu_lvl[].

Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 24 ++++++++++--------------
1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4052,7 +4052,6 @@ static void __init rcu_init_geometry(void)
{
ulong d;
int i;
- int j;
int rcu_capacity[MAX_RCU_LVLS + 1];

/*
@@ -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++) {
+ }
+ 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++) {
+ 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)
--
1.8.1.5

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