netdev - Re: [patch net-next v2 10/10] net: sched: add termination action to allow goto chain

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Date:   Tue, 16 May 2017 09:59:36 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jiri Pirko <jiri@...nulli.us>
CC:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, dsa@...ulusnetworks.com,
        edumazet@...gle.com, stephen@...workplumber.org,
        alexander.h.duyck@...el.com, simon.horman@...ronome.com,
        mlxsw@...lanox.com, alexei.starovoitov@...il.com
Subject: Re: [patch net-next v2 10/10] net: sched: add termination action
 to allow goto chain

On 05/16/2017 06:43 AM, Jiri Pirko wrote:
> Mon, May 15, 2017 at 10:02:08PM CEST, daniel@...earbox.net wrote:
>> On 05/15/2017 10:38 AM, Jiri Pirko wrote:
>>> From: Jiri Pirko <jiri@...lanox.com>
>>>
>>> Introduce new type of termination action called "goto_chain". This allows
>>> user to specify a chain to be processed. This action type is
>>> then processed as a return value in tcf_classify loop in similar
>>> way as "reclassify" is, only it does not reset to the first filter
>>> in chain but rather reset to the first filter of the desired chain.
>>>
>>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>> [...]
>>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>>> index 1112a2b..98cc689 100644
>>> --- a/net/sched/cls_api.c
>>> +++ b/net/sched/cls_api.c
>>> @@ -304,10 +304,14 @@ int tcf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
>>>    			continue;
>>>
>>>    		err = tp->classify(skb, tp, res);
>>> -		if (unlikely(err == TC_ACT_RECLASSIFY && !compat_mode))
>>> +		if (err == TC_ACT_RECLASSIFY && !compat_mode) {
>>>    			goto reset;
>>> -		if (err >= 0)
>>> +		} else if (TC_ACT_EXT_CMP(err, TC_ACT_GOTO_CHAIN)) {
>>> +			old_tp = res->goto_tp;
>>> +			goto reset;
>>> +		} else if (err >= 0) {
>>>    			return err;
>>> +		}
>>
>> Given this goto chain feature is pretty much only interesting for hw
>> offloads, can we move this further away from the sw fast path to not
>> add up to the cost per packet? (I doubt anyone is using TC_ACT_RECLASSIFY
>> in sw as well ...)
>
> I don't think so. First of all, the whole thing would be broken then in
> sw. It is useful to have it in sw, at least for testing reasons.
> So I would leave the unlikely and add it to the second check as well.

Ok, lets go with that then, thanks!