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 08:07:27 +0100
From:   Bartek Kois <bartek.kois@...il.com>
To:     Anton Danilov <littlesmilingcloud@...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

Is this equally fast as hashing tables?

Best regards
Bartek Kois
W dniu 03.01.2019 o 22:49, Anton Danilov pisze:
> 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.
>
>