Commit 4dc89133 authored Aug 31, 2010 by Eric Dumazet Committed by David S. Miller Aug 31, 2010

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 6cf3f41e (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>

parent ba4fd9d8

include/linux/netdevice.h

+8 −1

Original line number	Diff line number	Diff line
		@@ -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