netdev - Re: [Patch bpf-next v3 4/5] skmsg: use skb ext instead of TCP_SKB

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Message-ID: <CACAyw99k43REGCh8cP1PioV+k-_BRAjecVHcmtOdL6fi2shxkQ@mail.gmail.com>
Date:   Tue, 16 Feb 2021 08:56:11 +0000
From:   Lorenz Bauer <lmb@...udflare.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        duanxiongchun@...edance.com, wangdongdong.6@...edance.com,
        jiang.wang@...edance.com, Cong Wang <cong.wang@...edance.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [Patch bpf-next v3 4/5] skmsg: use skb ext instead of TCP_SKB_CB

On Mon, 15 Feb 2021 at 19:20, John Fastabend <john.fastabend@...il.com> wrote:
>
> Cong Wang wrote:
> > From: Cong Wang <cong.wang@...edance.com>
> >
> > Currently TCP_SKB_CB() is hard-coded in skmsg code, it certainly
> > does not work for any other non-TCP protocols. We can move them to
> > skb ext instead of playing with skb cb, which is harder to make
> > correct.
> >
> > Cc: John Fastabend <john.fastabend@...il.com>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: Jakub Sitnicki <jakub@...udflare.com>
> > Reviewed-by: Lorenz Bauer <lmb@...udflare.com>
> > Signed-off-by: Cong Wang <cong.wang@...edance.com>
> > ---
>
> I'm not seeing the advantage of doing this at the moment. We can
> continue to use cb[] here, which is simpler IMO and use the ext
> if needed for the other use cases. This is adding a per packet
> alloc cost that we don't have at the moment as I understand it.

John, do you have a benchmark we can look at? Right now we're arguing
in the abstract.