netdev - mpls_xmit() calls skb

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Message-id: <9F1B6AC3-509E-4C64-97A4-47247F25913A@apple.com>
Date: Fri, 08 Dec 2023 13:06:57 -0800
From: Christoph Paasch <cpaasch@...le.com>
To: netdev <netdev@...r.kernel.org>, Roopa Prabhu <roopa@...ulusnetworks.com>
Cc: Craig Taylor <cmtaylor@...le.com>
Subject: mpls_xmit() calls skb_orphan()

Hello,

we observed an issue when running a TCP-connection with BBR on top of an MPLS-tunnel in that we saw a lot of CPU-time spent coming from tcp_pace_kick(), although sch_fq was configured on this host.

The reason for this seems to be because mpls_xmit() calls skb_orphan(), thus settings skb->sk to NULL, preventing the qdisc to set sk_pacing_status (which would allow to avoid the call to tcp_pace_kick()).

The question is: Why is this call to skb_orphan in mpls_xmit necessary ?

Thanks,
Christoph