netdev - Re: [RFC 2/3] tc: deprecate TC_ACT

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Date:	Thu, 23 Apr 2015 15:33:31 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC 2/3] tc: deprecate TC_ACT_QUEUED

On Thu, Apr 23, 2015 at 3:13 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
> On 4/23/15 1:45 PM, Jamal Hadi Salim wrote:
>>
>>
>> 1) the _XMIT semantics are useful on the egress side because in fact
>> we do have queues and they can be attached to qdiscs etc.
>> The TC_ACT_XXX codes were _intentional_ since ingress works as a
>> classifier shell.
>
>
> then it is worse mess than I thought :(
> Why call it _qdisc_ then? and have special and convoluted handling for
> it in qdisc_create, qdisc_graft and other places?

It needs to glue into qdisc layer, unify the abstractions.

>
>> Are you planning to queue things on ingress?
>
> I thought that was the whole purpose of ingress qdisc.

There is no queue for ingress qdisc.

> why then we have dev->ingress_queue?

Glue layer, qdisc ties too much with txq, which is what I want to solve.

We have struct netdev_rx_queue too, but look at it, there is nothing
but some sysfs stuffs needed by RPS.

>
> If queueing was never a goal, may be we should kill ingress qdisc
> and replace it with a simple shim that only does cls/act.
> The code overall will get much simpler and faster.
>

As I said in response to your patch for skb->data, we need to align
ingress with egress, rather than making more differences, this includes
qdisc's too. We do have per-cpu queues for ingress, at least in theory
we have a queue for ingress to use.

Of course, RX is naturally different from TX, which is the root cause
why we have so many differences here.
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