netdev - Re: [PATCH bpf-next 2/2] xdp: Use bulking for non-map XDP

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Date:   Fri, 10 Jan 2020 16:54:30 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH bpf-next 2/2] xdp: Use bulking for non-map XDP_REDIRECT

On Fri, 10 Jan 2020 at 16:30, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> Björn Töpel <bjorn.topel@...il.com> writes:
>
[...]
> >
> > After these changes, does the noinline (commit 47b123ed9e99 ("xdp:
> > split code for map vs non-map redirect")) still make sense?
>
> Hmm, good question. The two code paths are certainly close to one
> another; and I guess they could be consolidated further.
>
> The best case would be if we had a way to lookup the ifindex directly in
> the helper. Do you know if there's a way to get the current net
> namespace from the helper? Can we use current->nsproxy->net_ns in that
> context?
>

Nope, interrupt context. :-( Another (ugly) way is adding a netns
member to the bpf_redirect_info, that is populated by the driver
(driver changes everywhere -- ick). So no.

(And *if* one would go the route of changing all drivers, I think the
percpu bpf_redirect_info should be replaced a by a context that is
passed from the driver to the XDP program execution and
xdp_do_redirect/flush. But that's a much bigger patch. :-))


Björn


> If we can, and if we don't mind merging the two different tracepoints,
> the xdp_do_redirect() function could be made quite a bit leaner...
>
> -Toke
>