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

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Date:   Sun, 5 Jul 2020 17:23:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Ariel Levkovich <lariel@...lanox.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>, Jiri Pirko <jiri@...lanox.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net-next v2 0/3] ] TC datapath hash api

On Sun, Jul 5, 2020 at 10:26 AM Ariel Levkovich <lariel@...lanox.com> wrote:
> However I believe that from a concept point of view, using it is wrong.
>
> In my honest opinion, the concept here is to perform some calculation on
> the packet itself and its headers while the skb->hash field
>
> is the storage location of the calculation result (in SW).

With skbedit, you don't have to pass a value either, whatever you
pass to your act_hash, you can pass it to skbedit too. In your case,
it seems to be an algorithm name.

You can take a look at SKBEDIT_F_INHERITDSFIELD, it calculates
skb->priority from headers, not passed from user-space.


>
> Furthermore, looking forward to HW offload support, the HW devices will
> be offloading the hash calculation and
>
> not rewriting skb metadata fields. Therefore the action should be the
> hash, not skbedit.

Not sure if this makes sense, whatever your code under case
TCA_HASH_ALG_L4 can be just moved to skbedit. I don't see
how making it standalone could be different for HW offloading.


>
> Another thing that I can mention, which is kind of related to what I
> wrote above, is that for all existing skbedit supported fields,
>
> user typically provides a desired value of his choosing to set to a skb
> metadata field.

Again, no one forces this rule. Please feel free to adjust it for your needs.

Thanks.