From 4dc89133f49b8cfd77ba7e83f5960aed63aaa99e Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 31 Aug 2010 07:40:16 +0000
Subject: [PATCH] net: add a comment on netdev->last_rx
As some driver authors seem to reintroduce dev->last_rx use,
add a comment to strongly discourage this.
Since commit 6cf3f41e6c0 (bonding, net: Move last_rx update into bonding
recv logic), network drivers dont need to update last_rx themselves,
unless they use this field to implement a timeout.
Not updating last_rx helps not dirtying a cache line, improving
performance in SMP.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
include/linux/netdevice.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 0cf9448a32c4..c82220a9f3d5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -953,7 +953,14 @@ struct net_device {
/*
* Cache line mostly used on receive path (including eth_type_trans())
*/
- unsigned long last_rx; /* Time of last Rx */
+ unsigned long last_rx; /* Time of last Rx
+ * This should not be set in
+ * drivers, unless really needed,
+ * because network stack (bonding)
+ * use it if/when necessary, to
+ * avoid dirtying this cache line.
+ */
+
/* Interface address info used in eth_type_trans() */
unsigned char *dev_addr; /* hw address, (before bcast
because most packets are
--
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