net: loopback: enable BIG TCP packets

Set the driver limit to GSO_MAX_SIZE (512 KB).

This allows the admin/user to set a GSO limit up to this value.

Tested:

ip link set dev lo gso_max_size 200000
netperf -H ::1 -t TCP_RR -l 100 -- -r 80000,80000 &

tcpdump shows :

18:28:42.962116 IP6 ::1 > ::1: HBH 40051 > 63780: Flags [P.], seq 3626480001:3626560001, ack 3626560001, win 17743, options [nop,nop,TS val 3771179265 ecr 3771179265], length 80000
18:28:42.962138 IP6 ::1.63780 > ::1.40051: Flags [.], ack 3626560001, win 17743, options [nop,nop,TS val 3771179265 ecr 3771179265], length 0
18:28:42.962152 IP6 ::1 > ::1: HBH 63780 > 40051: Flags [P.], seq 3626560001:3626640001, ack 3626560001, win 17743, options [nop,nop,TS val 3771179265 ecr 3771179265], length 80000
18:28:42.962157 IP6 ::1.40051 > ::1.63780: Flags [.], ack 3626640001, win 17743, options [nop,nop,TS val 3771179265 ecr 3771179265], length 0
18:28:42.962180 IP6 ::1 > ::1: HBH 40051 > 63780: Flags [P.], seq 3626560001:3626640001, ack 3626640001, win 17743, options [nop,nop,TS val 3771179265 ecr 3771179265], length 80000
18:28:42.962214 IP6 ::1.63780 > ::1.40051: Flags [.], ack 3626640001, win 17743, options [nop,nop,TS val 3771179266 ecr 3771179265], length 0
18:28:42.962228 IP6 ::1 > ::1: HBH 63780 > 40051: Flags [P.], seq 3626640001:3626720001, ack 3626640001, win 17743, options [nop,nop,TS val 3771179266 ecr 3771179265], length 80000
18:28:42.962233 IP6 ::1.40051 > ::1.63780: Flags [.], ack 3626720001, win 17743, options [nop,nop,TS val 3771179266 ecr 3771179266], length 0
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/loopback.c

@@ -191,6 +191,8 @@ static void gen_lo_setup(struct net_device *dev,
 	dev->netdev_ops		= dev_ops;
 	dev->needs_free_netdev	= true;
 	dev->priv_destructor	= dev_destructor;
+
+	netif_set_tso_max_size(dev, GSO_MAX_SIZE);
 }
 
 /* The loopback device is special. There is only one instance