linux-kernel - [PATCH] net: fold network name hash (v2)

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Date:	Tue, 27 Oct 2009 15:04:36 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, eric.dumazet@...il.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	opurdila@...acom.com, viro@...iv.linux.org.uk
Subject: [PATCH] net: fold network name hash (v2)

The full_name_hash does not produce a value that is evenly distributed
over the lower 8 bits. This causes name hash to be unbalanced with large
number of names. There is a standard function to fold in upper bits
so use that.

This is independent of possible improvements to full_name_hash()
in future.
 
Signed-off-by: Stephen Hemminger <shemminger@...tta.com>

--- a/net/core/dev.c	2009-10-27 14:54:21.922563076 -0700
+++ b/net/core/dev.c	2009-10-27 15:04:16.733813459 -0700
@@ -86,6 +86,7 @@
 #include <linux/socket.h>
 #include <linux/sockios.h>
 #include <linux/errno.h>
+#include <linux/hash.h>
 #include <linux/interrupt.h>
 #include <linux/if_ether.h>
 #include <linux/netdevice.h>
@@ -199,7 +200,7 @@ EXPORT_SYMBOL(dev_base_lock);
 static inline struct hlist_head *dev_name_hash(struct net *net, const char *name)
 {
 	unsigned hash = full_name_hash(name, strnlen(name, IFNAMSIZ));
-	return &net->dev_name_head[hash & ((1 << NETDEV_HASHBITS) - 1)];
+	return &net->dev_name_head[hash_long(hash, NETDEV_HASHBITS)];
 }
 
 static inline struct hlist_head *dev_index_hash(struct net *net, int ifindex)
--
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