[B.A.T.M.A.N.] [PATCH 01/14] batman-adv: Replace gw_reselect divisor with simple shift

Antonio Quartulli
2015-08-04T16:35:21Z

From: Sven Eckelmann <sven@narfation.org>

The gw_factor is divided by BATADV_TQ_LOCAL_WINDOW_SIZE ** 2 * 64. But the
rest of the calculation has nothing to do with the tq window size and
therefore the calculation is just (tmp_gw_factor / (64 ** 3)).

Replace it with a simple shift to avoid a costly 64-bit divide when the
max_gw_factor is changed from u32 to u64. This type change is necessary
to avoid an overflow bug.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
---
net/batman-adv/gateway_client.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index bb015862..e1e1f31 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -154,14 +154,10 @@ batadv_gw_get_best_gw_node(struct batadv_priv *bat_priv)
struct batadv_neigh_ifinfo *router_ifinfo;
struct batadv_gw_node *gw_node, *curr_gw = NULL;
uint32_t max_gw_factor = 0, tmp_gw_factor = 0;
- uint32_t gw_divisor;
uint8_t max_tq = 0;
uint8_t tq_avg;
struct batadv_orig_node *orig_node;

- gw_divisor = BATADV_TQ_LOCAL_WINDOW_SIZE * BATADV_TQ_LOCAL_WINDOW_SIZE;
- gw_divisor *= 64;
-
rcu_read_lock();
hlist_for_each_entry_rcu(gw_node, &bat_priv->gw.list, list) {
if (gw_node->deleted)
@@ -187,7 +183,7 @@ batadv_gw_get_best_gw_node(struct batadv_priv *bat_priv)
tmp_gw_factor = tq_avg * tq_avg;
tmp_gw_factor *= gw_node->bandwidth_down;
tmp_gw_factor *= 100 * 100;
- tmp_gw_factor /= gw_divisor;
+ tmp_gw_factor >>= 18;

if ((tmp_gw_factor > max_gw_factor) ||
((tmp_gw_factor == max_gw_factor) &&
--
2.5.0