netdev - Re: [Patch net-next v2 4/4] net_sched: kill u32

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Message-ID: <20170825090646.GB4829@nanopsycho>
Date:   Fri, 25 Aug 2017 11:06:46 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     netdev@...r.kernel.org, jhs@...atatu.com
Subject: Re: [Patch net-next v2 4/4] net_sched: kill u32_node pointer in Qdisc

Fri, Aug 25, 2017 at 01:51:30AM CEST, xiyou.wangcong@...il.com wrote:
>It is ugly to hide a u32-filter-specific pointer inside Qdisc,
>this breaks the TC layers:
>
>1. Qdisc is a generic representation, should not have any specific
>   data of any type
>
>2. Qdisc layer is above filter layer, should only save filters in
>   the list of struct tcf_proto.
>
>This pointer is used as the head of the chain of u32 hash tables,
>that is struct tc_u_hnode, because u32 filter is very special,
>it allows to create multiple hash tables within one qdisc and
>across multiple u32 filters.
>
>Instead of using this ugly pointer, we can just save it in a global
>hash table key'ed by (dev ifindex, qdisc handle), therefore we can
>still treat it as a per qdisc basis data structure conceptually.
>
>Of course, because of network namespaces, this key is not unique
>at all, but it is fine as we already have a pointer to Qdisc in
>struct tc_u_common, we can just compare the pointers when collision.
>
>And this only affects slow paths, has no impact to fast path,
>thanks to the pointer ->tp_c.
>
>Cc: Jamal Hadi Salim <jhs@...atatu.com>
>Cc: Jiri Pirko <jiri@...nulli.us>
>Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

Acked-by: Jiri Pirko <jiri@...lanox.com>