netdev - Re: [PATCH net-next v3 2/4] net/sched: Introduce action hash

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Message-ID: <CAM_iQpXy-_qVUangkd-V8V_shLRMjRNUpJkrWTZ=xv3sYzzaKQ@mail.gmail.com>
Date:   Mon, 13 Jul 2020 15:04:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Ariel Levkovich <lariel@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Jakub Kicinski <kuba@...nel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH net-next v3 2/4] net/sched: Introduce action hash

On Sat, Jul 11, 2020 at 2:28 PM Ariel Levkovich <lariel@...lanox.com> wrote:
>
> Allow user to set a packet's hash value using a bpf program.
>
> The user provided BPF program is required to compute and return
> a hash value for the packet which is then stored in skb->hash.

Can be done by act_bpf, right?

>
> Using this action to set the skb->hash is an alternative to setting
> it with act_skbedit and can be useful for future HW offload support
> when the HW hash function is different then the kernel's hash
> function.
> By using a bpg program that emulates the HW hash function user
> can ensure hash consistency between the SW and the HW.

It sounds weird that the sole reason to add a new action is
because of HW offloading. What prevents us extending the
existing actions to support HW offloading?

Thanks.