From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH RFC 1/2] tun: don't require serialization lock on tx Date: Wed, 13 Apr 2016 12:41:45 +0300 Message-ID: <20160413123828-mutt-send-email-mst@redhat.com> References: <425e8f69ffd8fe315ef9d3cc678519c7060fb2e0.1460393493.git.pabeni@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, "David S. Miller" , Hannes Frederic Sowa , "Eric W. Biederman" , Greg Kurz , Jason Wang , Christian Borntraeger , Herbert Xu To: Paolo Abeni Return-path: Received: from mx1.redhat.com ([209.132.183.28]:33590 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965886AbcDMJlu (ORCPT ); Wed, 13 Apr 2016 05:41:50 -0400 Content-Disposition: inline In-Reply-To: <425e8f69ffd8fe315ef9d3cc678519c7060fb2e0.1460393493.git.pabeni@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 > --- > 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 */ git log gives this explanation: > 1) unnecessary; > 2) causes problems with AF_PACKET seeing things twice. > dev->vlan_features = dev->features & > ~(NETIF_F_HW_VLAN_CTAG_TX | > NETIF_F_HW_VLAN_STAG_TX); > -- > 1.8.3.1