netdev - Re: [PATCH RFC 1/3] xdp: Infrastructure to generalize XDP

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Date:   Wed, 21 Sep 2016 01:09:27 +0200
From:   Thomas Graf <tgraf@...g.ch>
To:     Tom Herbert <tom@...bertland.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH RFC 1/3] xdp: Infrastructure to generalize XDP

On 09/20/16 at 03:49pm, Tom Herbert wrote:
> On Tue, Sep 20, 2016 at 3:44 PM, Thomas Graf <tgraf@...g.ch> wrote:
> > On 09/20/16 at 03:00pm, Tom Herbert wrote:
> >> +static inline int __xdp_hook_run(struct list_head *list_head,
> >> +                              struct xdp_buff *xdp)
> >> +{
> >> +     struct xdp_hook_ops *elem;
> >> +     int ret = XDP_PASS;
> >> +
> >> +     list_for_each_entry(elem, list_head, list) {
> >> +             ret = elem->hook(elem->priv, xdp);
> >> +             if (ret != XDP_PASS)
> >> +                     break;
> >> +     }
> >
> > Walking over a linear list? Really? :-) I thought this was supposed
> > to be fast, no compromises made.
> 
> Can you suggest an alternative?

Single BPF program that encodes whatever logic is required. This is
what BPF is for. If it absolutely has to run two programs in sequence
then it can still do that even though I really don't see much of a
point of doing that in a high performance environment.

I'm not even sure yet I understand full purpose of this yet ;-)