netdev - [PATCH 01/10] batman-adv: Replace gw_reselect divisor with simple shift

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Date:	Tue, 11 Aug 2015 18:35:39 +0200
From:	Antonio Quartulli <antonio@...hcoding.com>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, b.a.t.m.a.n@...ts.open-mesh.org,
	Sven Eckelmann <sven@...fation.org>,
	Marek Lindner <mareklindner@...mailbox.ch>,
	Antonio Quartulli <antonio@...hcoding.com>
Subject: [PATCH 01/10] batman-adv: Replace gw_reselect divisor with simple shift

From: Sven Eckelmann <sven@...fation.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@...fation.org>
Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@...hcoding.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

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