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Subject[PATCH v2 4/9] rcu: Simplify rcu_init_geometry() capacity arithmetics
Date
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>
---
kernel/rcu/tree.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0de0a34..b10e48e 100644
--- 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.
@@ -4106,12 +4106,10 @@ 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;

/*
@@ -4124,7 +4122,7 @@ static void __init rcu_init_geometry(void)
* the rcu_node masks. Complain and fall back to the compile-
* time values if these limits are exceeded.
*/
- 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");
else if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
rcu_fanout_leaf > sizeof(unsigned long) * 8) {
@@ -4133,13 +4131,13 @@ static void __init rcu_init_geometry(void)
}

/* 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);
}

--
1.8.3.1


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