On Wed, Apr 13, 2016 at 11:48:09AM +0200, Hannes Frederic Sowa wrote: > On 13.04.2016 11:41, Michael S. Tsirkin wrote: > >On Wed, Apr 13, 2016 at 11:04:46AM +0200, Paolo Abeni wrote: > >>The current tun_net_xmit() implementation don't need any external > >>lock since it relay on rcu protection for the tun data structure > >>and on socket queue lock for skb queuing. > >> > >>This patch set the NETIF_F_LLTX feature bit in the tun device, so > >>that on xmit, in absence of qdisc, no serialization lock is acquired > >>by the caller. > >> > >>Signed-off-by: Paolo Abeni <pab...@redhat.com> > >>--- > >> drivers/net/tun.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >>diff --git a/drivers/net/tun.c b/drivers/net/tun.c > >>index faf9297..42992dc 100644 > >>--- a/drivers/net/tun.c > >>+++ b/drivers/net/tun.c > >>@@ -1796,7 +1796,7 @@ static int tun_set_iff(struct net *net, struct file > >>*file, struct ifreq *ifr) > >> dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST | > >> TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX | > >> NETIF_F_HW_VLAN_STAG_TX; > >>- dev->features = dev->hw_features; > >>+ dev->features = dev->hw_features | NETIF_F_LLTX; > > > >the documentation says: > > NETIF_F_LLTX_BIT, /* LockLess TX - deprecated. > > Please */ > > /* do not use LLTX in new drivers */ > > In networking/netdev-features.txt > > * LLTX driver (deprecated for hardware drivers) > > NETIF_F_LLTX should be set in drivers that implement their own locking in > transmit path or don't need locking at all (e.g. software tunnels). > In ndo_start_xmit, it is recommended to use a try_lock and return > NETDEV_TX_LOCKED when the spin lock fails. The locking should also properly > protect against other callbacks (the rules you need to find out). > > Don't use it for new drivers. > > I think this is documentation is correct and it is only deprecated for > hardware drivers. > > Bye, > Hannes
Fine, but what's the AF_PACKET duplication that Herbert Xu reported with NETIF_F_LLTX? Does anyone remember? -- MST
