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Date: Wed, 05 May 2010 07:24:09 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>, jamal <hadi@...erus.ca>,
Tom Herbert <therbert@...gle.com>
Subject: [PATCH net-next-2.6] net: Increase NET_SKB_PAD to 64 bytes
eth_type_trans() & get_rps_cpus() currently need two 64bytes cache lines
in packet to compute rxhash.
Increasing NET_SKB_PAD from 32 to 64 reduces the need to one cache line
only, and makes RPS faster.
NET_IP_ALIGN(2) + ethernet_header(14) + IP_header(20/40) + ports(8)
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 746a652..fe5798b 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1356,9 +1356,12 @@ static inline int skb_network_offset(const struct sk_buff *skb)
*
* Various parts of the networking layer expect at least 32 bytes of
* headroom, you should not reduce this.
+ * With RPS, we raised NET_SKB_PAD to 64 so that get_rps_cpus() fetches span
+ * a 64 bytes aligned block to fit modern (>= 64 bytes) cache line sizes
+ * NET_IP_ALIGN(2) + ethernet_header(14) + IP_header(20/40) + ports(8)
*/
#ifndef NET_SKB_PAD
-#define NET_SKB_PAD 32
+#define NET_SKB_PAD 64
#endif
extern int ___pskb_trim(struct sk_buff *skb, unsigned int len);
--
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