+/*
+ * Compute the rcu_node tree geometry from kernel parameters. This cannot
+ * replace the definitions in rcutree.h because those are needed to size
+ * the ->node array in the rcu_state structure.
+ */
+static void __init rcu_init_geometry(void)
+{
+ int i;
+ int j;
+ int n = NR_CPUS;
+ int rcu_capacity[MAX_RCU_LVLS + 1];
+
+ /* If the compile-time values are accurate, just leave. */
+ if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF)
+ return;
+
+ /*
+ * 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.
+ */
+ rcu_capacity[0] = 1;
+ rcu_capacity[1] = rcu_fanout_leaf;
+ for (i = 2; i <= MAX_RCU_LVLS; i++)
+ rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
+
+ /*
+ * The boot-time rcu_fanout_leaf parameter is only permitted
+ * to increase the leaf-level fanout, not decrease it. Of course,
+ * the leaf-level fanout cannot exceed the number of bits in
+ * the rcu_node masks. Finally, the tree must be able to accommodate
+ * the configured number of CPUs. Complain and fall back to the
+ * compile-time values if these limits are exceeded.
+ */
+ if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
+ rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
+ n > rcu_capacity[MAX_RCU_LVLS]) {
+ WARN_ON(1);
+ return;
+ }
+
+ /* Calculate the number of rcu_nodes at each level of the tree. */
+ for (i = 1; i <= MAX_RCU_LVLS; i++)
+ if (n <= rcu_capacity[i]) {
+ for (j = 0; j <= i; j++)
+ num_rcu_lvl[j] =
+ DIV_ROUND_UP(n, rcu_capacity[i - j]);
+ rcu_num_lvls = i;
+ for (j = i + 1; j <= MAX_RCU_LVLS; j++)
+ num_rcu_lvl[j] = 0;
+ break;
+ }
+
+ /* Calculate the total number of rcu_node structures. */
+ rcu_num_nodes = 0;
+ for (i = 0; i <= MAX_RCU_LVLS; i++)
+ rcu_num_nodes += num_rcu_lvl[i];
+ rcu_num_nodes -= n;
+}
+