netdev - Re: [PATCH bpf-next 0/9] bpf: cpumap: enable GRO for XDP

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Message-ID: <Ztnj9ujDg4NLZFDm@lore-desk>
Date: Thu, 5 Sep 2024 19:01:42 +0200
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>, Daniel Xu <dxu@...uu.xyz>,
	John Fastabend <john.fastabend@...il.com>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	bpf@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 0/9] bpf: cpumap: enable GRO for XDP_PASS frames

> > On Fri, 30 Aug 2024 18:24:59 +0200 Alexander Lobakin wrote:
> > > * patch 4: switch cpumap from a custom kthread to a CPU-pinned
> > >   threaded NAPI;
> > 
> > Could you try to use the backlog NAPI? Allocating a fake netdev and
> > using NAPI as a threading abstraction feels like an abuse. Maybe try
> > to factor out the necessary bits? What we want is using the per-cpu 
> > caches, and feeding GRO. None of the IRQ related NAPI functionality
> > fits in here.
> 
> I was thinking allocating a fake netdev to use NAPI APIs is quite a common
> approach, but sure, I will looking into it.

From a first glance I think we could use the backlog NAPI APIs here in
order to avoid allocating a dummy netdev. We could implement a similar
approach I used for the cpumap + gro_cell here [0].
In particular, the cpumap kthread pinned on cpu 'n' can schedule the
backlog NAPI associated to cpu 'n'. However according to my understanding
it seems the backlog NAPI APIs (in process_backlog()) do not support GRO,
right? Am I missing something?

Regards,
Lorenzo

[0] https://github.com/LorenzoBianconi/bpf-next/commit/a4b8264d5000ecf016da5a2dd9ac302deaf38b3e

> 
> Regards,
> Lorenzo



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