netdev - Re: Qdisc->u32_node

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Message-ID: <20170809124834.GC1867@nanopsycho>
Date:   Wed, 9 Aug 2017 14:48:34 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        mlxsw@...lanox.com
Subject: Re: Qdisc->u32_node - licence to kill

Wed, Aug 09, 2017 at 02:40:30PM CEST, jhs@...atatu.com wrote:
>On 17-08-07 07:21 PM, Cong Wang wrote:
>> On Mon, Aug 7, 2017 at 12:54 PM, John Fastabend
>> <john.fastabend@...il.com> wrote:
>> > On 08/07/2017 12:06 PM, Jiri Pirko wrote:
>> > > Mon, Aug 07, 2017 at 07:47:14PM CEST, john.fastabend@...il.com wrote:
>> > > > On 08/07/2017 09:41 AM, Jiri Pirko wrote:
>> > > > > Hi Jamal/Cong/David/all.
>> > > > > 
>=
>> > > 
>> > > Not correct. prio/pref is one level up priority, independent on specific
>> > > cls implementation. You can have cls_u32 instance on prio 10 and
>> > > cls_flower instance on prio 20. Both work.
>> > 
>> > ah right, lets make sure I got this right then (its been awhile since I've
>> > read this code). So the tcf_ctl_tfilter hook walks classifiers, inserting the
>> > classifier by prio. Then tcf_classify walks the list of classifiers looking
>> > for any matches, specifically any return codes it recognizes or a return code
>> > greater than zero. u32 though has this link notion that allows users to jump
>> > to other u32 classifiers that are in this list, because it has a global hash
>> > table list. So the per prio classifier isolation is not true in u32 case.
>> 
>> u32 filter supports multiple hash tables within a qdisc, struct
>> tc_u_common is supposed to link them together. This has to be
>> per qdisc because all of these hash tables belong to one qdisc
>> and their ID's are unique within the qdisc.
>> 
>
>I think historically this used to sit within the u32 code as a
>static linked list; i cant recall why it got attached to the
>qdisc.
>Indeed, the idea is that hash tables can be added independently
>without linking and then linked afterwards. They have to be held
>somewhere in transient. And they have priorities (at least the
>prios are used in the dump)
>
>> I dislike it too, and I actually tried to improve it in the past,
>> unfortunately didn't make any real progress. I think we can
>> definitely make it less ugly, but I don't think we can totally
>> get rid of it because of the design of u32.
>> 
>> Similar for tp->data.
>> 
>
>tp->q maybe harder to deal with. I agree with getting rid of
>this dependency. Could this info be stored in the block instead?

Yeah, I will have to do that. I just wanted to get rid of it if possible :/


>
>cheers,
>jamal