From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH RFC 2/2] tun: don't set a default qdisc Date: Thu, 14 Apr 2016 14:49:28 +0800 Message-ID: <570F3D78.3070203@redhat.com> References: <1a216fb6cade7dcd7d2c1d4ce113a1ee6e3fdeb6.1460393493.git.pabeni@redhat.com> <20160413132411-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, "David S. Miller" , Hannes Frederic Sowa , "Eric W. Biederman" , Greg Kurz To: "Michael S. Tsirkin" , Paolo Abeni Return-path: Received: from mx1.redhat.com ([209.132.183.28]:45861 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752793AbcDNGtg (ORCPT ); Thu, 14 Apr 2016 02:49:36 -0400 In-Reply-To: <20160413132411-mutt-send-email-mst@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 04/13/2016 06:26 PM, Michael S. Tsirkin wrote: > On Wed, Apr 13, 2016 at 11:04:47AM +0200, Paolo Abeni wrote: >> This patch disables the default qdisc by explicitly setting the >> IFF_NO_QUEUE private flag so that now the tun xmit path do not >> require any lock by default. >> >> The default qdisc was first removed as a side effect of commit >> f84bb1eac027 ("net: fix IFF_NO_QUEUE for drivers using alloc_netdev") >> and recently restored with commit 016adb7260f4 ("tuntap: restore default qdisc") >> >> Signed-off-by: Paolo Abeni > I wonder about this back and forth. > Jason, do you see a workload where the default qdisc > is preferable? I don't know, but we used to behave like this so we'd better keep it. An interesting thing is I vaguely remember that you have some concern when I propose IFF_NO_QUEUE for macvtap[1] :) I think this could be done by management or more safe by introducing a new tun flag (TUN_NO_QUEUE). [1] https://lkml.org/lkml/2015/8/24/147 > >> --- >> drivers/net/tun.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >> index 42992dc..0a0b63c 100644 >> --- a/drivers/net/tun.c >> +++ b/drivers/net/tun.c >> @@ -1081,6 +1081,7 @@ static void tun_net_init(struct net_device *dev) >> >> break; >> } >> + dev->priv_flags |= IFF_NO_QUEUE; >> } >> >> /* Character device part */ >> -- >> 1.8.3.1