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From: Eric Dumazet <edumazet@google.com>
Date: Tue, 23 Apr 2024 12:15:55 +0200
Message-ID: <CANn89i+6xRe4V6aDmD-9EM0uD7A87f6rzg3S7Xq6-NaB_Mb4nw@mail.gmail.com>
Subject: Re: [RFC] net: add TCP fraglist GRO support
To: Felix Fietkau <nbd@nbd.name>
Cc: netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>, 
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>, David Ahern <dsahern@kernel.org>, 
	linux-kernel@vger.kernel.org
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On Tue, Apr 23, 2024 at 11:41=E2=80=AFAM Felix Fietkau <nbd@nbd.name> wrote=
:
>
> When forwarding TCP after GRO, software segmentation is very expensive,
> especially when the checksum needs to be recalculated.
> One case where that's currently unavoidable is when routing packets over
> PPPoE. Performance improves significantly when using fraglist GRO
> implemented in the same way as for UDP.
>
> Here's a measurement of running 2 TCP streams through a MediaTek MT7622
> device (2-core Cortex-A53), which runs NAT with flow offload enabled from
> one ethernet port to PPPoE on another ethernet port + cake qdisc set to
> 1Gbps.
>
> rx-gro-list off: 630 Mbit/s, CPU 35% idle
> rx-gro-list on:  770 Mbit/s, CPU 40% idle

Hi Felix

changelog is a bit terse, and patch complex.

Could you elaborate why this issue
seems to be related to a specific driver ?

I think we should push hard to not use frag_list in drivers :/

And GRO itself could avoid building frag_list skbs
in hosts where forwarding is enabled.

(Note that we also can increase MAX_SKB_FRAGS to 45 these days)