netdev - Re: Why do we prefer skb->priority to tc filters?

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Date:	Wed, 11 Mar 2015 12:18:16 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	David Miller <davem@...emloft.net>
Subject: Re: Why do we prefer skb->priority to tc filters?

On Wed, Mar 11, 2015 at 11:25 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2015-03-11 at 11:08 -0700, Cong Wang wrote:
>> On Wed, Mar 11, 2015 at 10:34 AM, Cong Wang <cwang@...pensource.com> wrote:
>> >
>> > Given that skb->priority can be specified in user-space, doesn't this
>> > mean some application can always override our rules specified by tc
>> > filters? I think we should always respect tc filters over any
>> > application setting.
>> >
>>
>> Hmm, on the other hand, skb->priority can be changed in cgroup
>> too, in this case the current behavior seems correct. :-/ Interesting.
>
> Note that even HTB has the following code :
>

I am not surprised.

[...]

>
> So if skb->priority happens to match sch->handle or any class handle,
> we queue packet into a queue, without calling tc_classify()

This is exactly why I am asking, kernel respects user's choice so much
that it could override even both cgroup prio and tc filters, I don't know
what is the reason behind, but this means our tc filters can not work
with an application which sets skb->priority. For example, our tc filters
classify the packets from this socket into flow 1:1, but application
sets 1:2 by itself...
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