rcu: Simplify rcu_init_geometry() capacity arithmetics

Current code suggests that introducing the extra level to
rcu_capacity[] array makes some of the arithmetic easier.
Well, in fact it appears rather confusing and unnecessary.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 37ca8a867a1c0ee99dcebe68715dd7b80afbc920..2103beedb49fa844cdc2e141c5e41f056f70f268 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4082,7 +4082,7 @@ static void __init rcu_init_geometry(void)
 {
        ulong d;
        int i;
-       int rcu_capacity[MAX_RCU_LVLS + 1];
+       int rcu_capacity[MAX_RCU_LVLS];
 
        /*
         * Initialize any unspecified boot parameters.
@@ -4119,29 +4119,27 @@ static void __init rcu_init_geometry(void)
 
        /*
         * Compute number of nodes that can be handled an rcu_node tree
-        * with the given number of levels.  Setting rcu_capacity[0] makes
-        * some of the arithmetic easier.
+        * with the given number of levels.
         */
-       rcu_capacity[0] = 1;
-       rcu_capacity[1] = rcu_fanout_leaf;
-       for (i = 2; i <= MAX_RCU_LVLS; i++)
+       rcu_capacity[0] = rcu_fanout_leaf;
+       for (i = 1; i < MAX_RCU_LVLS; i++)
                rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
 
        /*
         * The tree must be able to accommodate the configured number of CPUs.
         * If this limit is exceeded than we have a serious problem elsewhere.
         */
-       if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS])
+       if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS - 1])
                panic("rcu_init_geometry: rcu_capacity[] is too small");
 
        /* Calculate the number of levels in the tree. */
-       for (i = 1; nr_cpu_ids > rcu_capacity[i]; i++) {
+       for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
        }
-       rcu_num_lvls = i;
+       rcu_num_lvls = i + 1;
 
        /* Calculate the number of rcu_nodes at each level of the tree. */
        for (i = 0; i < rcu_num_lvls; i++) {
-               int cap = rcu_capacity[rcu_num_lvls - i];
+               int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
                num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
        }