netdev - Re: [PATCH net-next 3/4] bpf: BPF for lightweight tunnel encapsulation

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Message-ID: <20161031125906.GB32374@pox.localdomain>
Date:   Mon, 31 Oct 2016 13:59:07 +0100
From:   Thomas Graf <tgraf@...g.ch>
To:     Tom Herbert <tom@...bertland.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        roopa <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net-next 3/4] bpf: BPF for lightweight tunnel
 encapsulation

On 10/30/16 at 06:28pm, Tom Herbert wrote:
> Right, that's why we rely on a dst cache. Any use of LWT that
> encapsulates or tunnels to a fixed destination (ILA, VXLAN, IPIP,
> etc.) would want to use the dst cache optimization to avoid the second
> lookup. The ILA LWT code used to call orig output and that worked as
> long as we could set the default router as the gateway "via". It was
> something we were able to deploy, but not a general solution.
> Integrating properly with routing gives a much better solution IMO.
> Note that David Lebrun's latest LWT Segment Routing patch does the
> second lookup with the dst cache to try to avoid it.

Noticed while implementing this: How does ILA ensure that dst_output()
is not invoked in a circular manner?

dstA->output() -> dstB->otuput() -> dstA->output() -> ...