netdev - Re: Problem with queuing vlan tagged packets after migration from 3.16.0 to 4.9.0

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Date:   Fri, 4 Jan 2019 00:49:34 +0300
From:   Anton Danilov <littlesmilingcloud@...il.com>
To:     Bartek Kois <bartek.kois@...il.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Problem with queuing vlan tagged packets after migration from
 3.16.0 to 4.9.0

Hi.
There is the workaround - classify the packets with iptables+ipset -
it's enough fast and more friendly.

On Fri, 4 Jan 2019 at 00:21, Bartek Kois <bartek.kois@...il.com> wrote:
>
> Hi
> 1. What exactly caused this change in the kernel?
> 2. I don`t understand why adding VLAN tag, which is just 4  additional
> bytes to the passing packet make it impossible to classify.
> 3. This whole thing makes the QoS under Linux routers hard to configure
> in scenarios with more than one VLAN which is pretty much every slightly
> bigger router nowadays especially if we use IFB and hashing filters. Is
> there any walkaround for that problem?
>
> Best regards
> Bartek Kois
>
> W dniu 03.01.2019 o 04:30, Cong Wang pisze:
> > On Tue, Jan 1, 2019 at 11:46 AM Bartek Kois <bartek.kois@...il.com> wrote:
> >> Hi
> >> Yes it did work since I remember (like around 2.4.x) and it changed
> >> since I moved from Debian 8 to 9. I would appreciate fixing that in the
> >> future beacuse it is essential for queueing traffic on the routers, but
> >> the question is why these filters don`t work in that case:
> >>
> >>       tc filter add dev $LAN_ETH parent 1:0 protocol ip prio 4 u32 match
> >> u32 0x0a000c08 0xffffffff at 20 classid 1:2001      # for 10.0.12.8 ip
> >> address
> >>       tc filter add dev $LAN_ETH parent 1:0 protocol ip prio 4 u32 match
> >> u32 0x0a000c09 0xffffffff at 20 classid 1:2002      # for 10.0.12.9 ip
> >> address
> >>       tc filter add dev $LAN_ETH parent 1:0 protocol ip prio 4 u32 match
> >> u32 0x0a000c10 0xffffffff at 20 classid 1:2003      # for 10.0.12.10 ip
> >> address
> >>
> >> I`ve changed "at 16" which works without vlan tags to "at 20" to take
> >> vlan tag into account.
> > Yeah, this confirms my speculation.
> >
> > The problem is essentially a design flaw of u32 filter, the IP header
> > and TCP header offsets are never fixed, for example VLAN tagging and
> > IP options. What's more, it is not easy for user-space to learn the offset
> > for different packets as it requires to parse into each packets.
> >
> > I don't know whether we can fix this either, VLAN call path probably
> > already makes assumptions on the current skb->data position, if
> > we "fix" it for u32, it would probably break other things.



-- 
Anton.