netdev - Re: [PATCH RFC bpf-next 32/52] bpf, cpumap: switch to GRO from netif_receive_skb

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Message-Id: <cadda351-6e93-4568-ba26-21a760bf9a57@app.fastmail.com>
Date: Wed, 07 Aug 2024 13:38:03 -0700
From: "Daniel Xu" <dxu@...uu.xyz>
To: "Alexander Lobakin" <alexandr.lobakin@...el.com>,
 "Alexei Starovoitov" <ast@...nel.org>,
 "Daniel Borkmann" <daniel@...earbox.net>,
 "Andrii Nakryiko" <andrii@...nel.org>
Cc: "Larysa Zaremba" <larysa.zaremba@...el.com>,
 "Michal Swiatkowski" <michal.swiatkowski@...ux.intel.com>,
 "Jesper Dangaard Brouer" <hawk@...nel.org>,
 Björn Töpel <bjorn@...nel.org>,
 "Magnus Karlsson" <magnus.karlsson@...el.com>,
 "Maciej Fijalkowski" <maciej.fijalkowski@...el.com>,
 "Jonathan Lemon" <jonathan.lemon@...il.com>,
 "toke@...hat.com" <toke@...hat.com>, "Lorenzo Bianconi" <lorenzo@...nel.org>,
 "David Miller" <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>,
 "Jakub Kicinski" <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>,
 "Jesse Brandeburg" <jesse.brandeburg@...el.com>,
 "John Fastabend" <john.fastabend@...il.com>,
 "Yajun Deng" <yajun.deng@...ux.dev>, "Willem de Bruijn" <willemb@...gle.com>,
 "bpf@...r.kernel.org" <bpf@...r.kernel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, xdp-hints@...-project.net
Subject: Re: [PATCH RFC bpf-next 32/52] bpf, cpumap: switch to GRO from
 netif_receive_skb_list()

Hi Alexander,

On Tue, Jun 28, 2022, at 12:47 PM, Alexander Lobakin wrote:
> cpumap has its own BH context based on kthread. It has a sane batch
> size of 8 frames per one cycle.
> GRO can be used on its own, adjust cpumap calls to the
> upper stack to use GRO API instead of netif_receive_skb_list() which
> processes skbs by batches, but doesn't involve GRO layer at all.
> It is most beneficial when a NIC which frame come from is XDP
> generic metadata-enabled, but in plenty of tests GRO performs better
> than listed receiving even given that it has to calculate full frame
> checksums on CPU.
> As GRO passes the skbs to the upper stack in the batches of
> @gro_normal_batch, i.e. 8 by default, and @skb->dev point to the
> device where the frame comes from, it is enough to disable GRO
> netdev feature on it to completely restore the original behaviour:
> untouched frames will be being bulked and passed to the upper stack
> by 8, as it was with netif_receive_skb_list().
>
> Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> ---
>  kernel/bpf/cpumap.c | 43 ++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 38 insertions(+), 5 deletions(-)
>

AFAICT the cpumap + GRO is a good standalone improvement. I think
cpumap is still missing this.

I have a production use case for this now. We want to do some intelligent
RX steering and I think GRO would help over list-ified receive in some cases.
We would prefer steer in HW (and thus get existing GRO support) but not all
our NICs support it. So we need a software fallback.

Are you still interested in merging the cpumap + GRO patches?

Thanks,
Daniel