netdev - Re: [PATCH net-next v2 0/3] ] TC datapath hash api

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Message-ID: <20200708144508.GB3667@nanopsycho.orion>
Date:   Wed, 8 Jul 2020 16:45:08 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Ariel Levkovich <lariel@...lanox.com>, netdev@...r.kernel.org,
        kuba@...nel.org, xiyou.wangcong@...il.com, ast@...nel.org,
        daniel@...earbox.net
Subject: Re: [PATCH net-next v2 0/3] ] TC datapath hash api

Wed, Jul 08, 2020 at 03:54:14PM CEST, jhs@...atatu.com wrote:
>On 2020-07-07 6:05 a.m., Jiri Pirko wrote:
>> Fri, Jul 03, 2020 at 01:22:47PM CEST, jhs@...atatu.com wrote:
>> > Hi,
>> > 
>> > Several comments:
>> > 1) I agree with previous comments that you should
>> > look at incorporating this into skbedit.
>> > Unless incorporating into skbedit introduces huge
>> > complexity, IMO it belongs there.
>> > 
>> > 2) I think it would make sense to create a skb hash classifier
>> > instead of tying this entirely to flower i.e i should not
>> > have to change u32 just so i can support hash classification.
>> 
>> Well, we don't have multiple classifiers for each flower match, we have
>> them all in one classifier.
>
>Packet data matches, yes - makes sense. You could argue the same for
>the other classifiers.
>
>> It turned out to be very convenient and
>> intuitive for people to use one classifier to do the job for them.
>
>IMO:
>For this specific case where _offload_ is the main use case i think
>it is not a good idea because flower on ingress is slow.

Eh? What do you mean by that?


>The goal of offloading classifiers to hardware is so one can reduce
>consumed cpu cycles on the host. If the hardware
>has done the classification for me, a simple hash lookup of the
>32 bit skbhash(similar to fw) in the host would be a lot less
>compute intensive than running flower's algorithm.

It is totally up to the driver/fw how they decide to offload flower.
There are multiple ways. So I don't really follow what do you mean by
"flower's algorithm"


>
>I think there is a line for adding everything in one place,
>my main concern is that this feature this is needed
>by all classifiers and not just flower.

"All" is effectively only flower. Let's be clear about that.


>
>
>> Modularity is nice, but useability is I think more important in this
>> case. Flower turned out to do good job there.
>> 
>
>For humans, agreed everything in one place is convinient.
>Note: your arguement could be used for "ls" to include "grep"
>functionality because in my scripts I do both most of the time.
>
>cheers,
>jamal
>
>
>
>> + Nothing stops you from creating separate classifier to match on hash
>> as you wanted to :)
>> 
>>