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

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Message-ID: <20170516044319.GA24493@nanopsycho>
Date:   Tue, 16 May 2017 06:43:19 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Daniel Borkmann <daniel@...earbox.net>
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

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.


>
>>   	}
>> 
>>   	return TC_ACT_UNSPEC; /* signal: continue lookup */
>>