netdev - Re: [net-next PATCH] veth: don't assign a qdisc to veth

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Date:	Fri, 03 Oct 2014 14:56:04 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	brouer@...hat.com, cwang@...pensource.com, netdev@...r.kernel.org,
	jpirko@...hat.com, mpatel@...hat.com
Subject: Re: [net-next PATCH] veth: don't assign a qdisc to veth

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 03 Oct 2014 13:51:59 -0700

> On Fri, 2014-10-03 at 22:38 +0200, Jesper Dangaard Brouer wrote:
>> On Fri, 3 Oct 2014 09:53:16 -0700
>> Cong Wang <cwang@...pensource.com> wrote:
>> 
>> > On Fri, Oct 3, 2014 at 3:48 AM, Jesper Dangaard Brouer
>> > <brouer@...hat.com> wrote:
>> > > The veth driver is a virtual device, and should not have assigned
>> > > the default qdisc.  Verified (ndo_start_xmit) veth_xmit can only
>> > > return NETDEV_TX_OK, thus this should be safe to bypass qdisc.
>> > >
>> > > Not assigning a qdisc is subtly done by setting tx_queue_len to zero.
>> > >
>> > 
>> > Huh?? Maybe your $subject is too misleading, but we do use HTB
>> > on veth, this will break our code since we will have to set tx_queue_len
>> > after your patch, no?
>> 
>> No, you HTB setup should still work.
> 
> Unfortunately no....
> 
> Default htb classes are pfifo, and this uses device txqueuelen as
> default limit.
> 
> So your change should have been done years ago.
> 
> Now its too late as it can break existing user scripts.

Agreed, this change cannot be made.
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