netdev - Re: [PATCH v3 net-next 0/3] flow_offload: Re-add per-action statistics

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Date:   Fri, 24 May 2019 18:27:39 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        "Pablo Neira Ayuso" <pablo@...filter.org>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "Andy Gospodarek" <andy@...yhouse.net>,
        Michael Chan <michael.chan@...adcom.com>,
        Vishal Kulkarni <vishal@...lsio.com>
Subject: Re: [PATCH v3 net-next 0/3] flow_offload: Re-add per-action
 statistics

On 24/05/2019 18:03, Jakub Kicinski wrote:
> On Fri, 24 May 2019 14:57:24 +0100, Edward Cree wrote:
>> Argh, there's a problem: an action doesn't have a (directly) associated
>>  block, and all the TC offload machinery nowadays is built around blocks.
>> Since this action might have been used in _any_ block (and afaik there's
>>  no way, from the action, to find which) we'd have to make callbacks on
>>  _every_ block in the system, which sounds like it'd perform even worse
>>  than the rule-dumping approach.
>> Any ideas?
> Simplest would be to keep a list of offloaders per action, but maybe
> something more clever would appear as one rummages through the code.
Problem with that is where to put the list heads; you'd need something that
 was allocated per action x block, for those blocks on which at least one
 offloader handled the rule (in_hw_count > 0).
Then you'd also have to update that when a driver bound/unbound from a
 block (fl_reoffload() time).
Best I can think of is keeping the cls_flower.rule allocated in
 fl_hw_replace_filter() around instead of immediately freeing it, and
 having a list_head in each flow_action_entry.  But that really looks like
 an overcomplicated mess.
TBH I'm starting to wonder if just calling all tc blocks in existence is
 really all that bad.  Is there a plausible use case with huge numbers of
 bound blocks?

-Ed