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

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Message-ID: <f23131c1-aae2-4c04-a60e-801ed1970be8@intel.com>
Date: Wed, 4 Sep 2024 15:13:54 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
	<daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Lorenzo Bianconi
	<lorenzo@...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

From: Jakub Kicinski <kuba@...nel.org>
Date: Tue, 3 Sep 2024 13:51:58 -0700

> 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.

Lorenzo will try as he wrote. I can only add that in my old tree, I
factored out GRO bits and used them here just as you wrote. The perf was
the same, but the diffstat was several hundred lines only to factor out
stuff, while here the actual switch to NAPI removes more lines than
adds, also custom kthread logic is gone etc. It just looks way more
elegant and simple.
I could say that gro_cells also "abuses" NAPI the same way, don't you
think? But nobody ever objected :>

Thanks,
Olek