From: Yuya Kusakabe <yuya.kusakabe@gmail.com>
To: edumazet@google.com
Cc: andrea.mayer@uniroma2.it, davem@davemloft.net, kuba@kernel.org,
pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next] seg6: reallocate the skb head on L2 encapsulation only when needed
Date: Thu, 3 Sep 2026 14:09:05 +0900 [thread overview]
Message-ID: <20260903130525.28296-1-yuya.kusakabe@gmail.com> (raw)
In-Reply-To: <CANn89iKUqjbrRkr68+S9nKAu49C3K01e3XSNwkY1NCgmuPMPag@mail.gmail.com>
On Wed, Sep 2, 2026 at 11:00 AM Eric Dumazet <edumazet@google.com> wrote:
> This is a nice improvement for forwarded traffic, but locally
> generated TCP traffic
> is still hitting two expensive reallocations (second one in
> __seg6_do_srh_encap())
>
> Can we combine needed headrooms so that only a single re-alloc occurs?
Thanks for looking at this. I will send a v2 with the combined
headroom.
One clarification on the locally generated case: seg6_build_state()
does not redirect the output path for the L2 modes, so locally
generated traffic never reaches this branch:
newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
if (tuninfo->mode != SEG6_IPTUN_MODE_L2ENCAP &&
tuninfo->mode != SEG6_IPTUN_MODE_L2ENCAP_RED)
newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
Two reallocations do happen on the forwarded path, though: with a
header-cloned skb whose headroom is below the total, asking only for
skb->mac_len leaves the second reallocation to __seg6_do_srh_encap(),
because the cow that unclones the skb does not also make room for the
outer header. So the combined headroom is the right shape either way.
prev parent reply other threads:[~2026-09-03 5:09 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-02 8:34 [PATCH net-next] seg6: reallocate the skb head on L2 encapsulation only when needed Yuya Kusakabe
2026-09-02 9:00 ` Eric Dumazet
2026-09-03 5:09 ` Yuya Kusakabe [this message]
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