netdev - Re: [PATCH net-next] mpls: Do not orphan the skb

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Message-ID: <CANn89iLrwYrKy7LEb+tpq=gSB9pn6M5jwtW_VE2LSxd6DoZL8w@mail.gmail.com>
Date: Wed, 6 Mar 2024 19:40:16 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Christoph Paasch <cpaasch@...le.com>
Cc: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, Roopa Prabhu <roopa@...dia.com>, 
	Craig Taylor <cmtaylor@...le.com>
Subject: Re: [PATCH net-next] mpls: Do not orphan the skb

On Wed, Mar 6, 2024 at 7:11 PM Christoph Paasch <cpaasch@...le.com> wrote:
>
> We observed that TCP-pacing was falling back to the TCP-layer pacing
> instead of utilizing sch_fq for the pacing. This causes significant
> CPU-usage due to the hrtimer running on a per-TCP-connection basis.
>
> The issue is that mpls_xmit() calls skb_orphan() and thus sets
> skb->sk to NULL. Which implies that many of the goodies of TCP won't
> work. Pacing falls back to TCP-layer pacing. TCP Small Queues does not
> work, ...
>
> It is safe to remove this call to skb_orphan() in mpls_xmit() as there
> really is not reason for it to be there. It appears that this call to
> skb_orphan comes from the very initial implementation of MPLS.
>
> Cc: Roopa Prabhu <roopa@...dia.com>
> Reported-by: Craig Taylor <cmtaylor@...le.com>
> Signed-off-by: Christoph Paasch <cpaasch@...le.com>
> ---

This seems reasonable to me, thanks.

Packets are immediately sent, there is no queue.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>