linux-kernel - Re: [RFC PATCH net-next 0/2] net: Use SMP threads for backlog NAPI.

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Message-ID: <20230818145734.OgLYhPh1@linutronix.de>
Date:   Fri, 18 Aug 2023 16:57:34 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Yan Zhai <yan@...udflare.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wander Lairson Costa <wander@...hat.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>
Subject: Re: [RFC PATCH net-next 0/2] net: Use SMP threads for backlog NAPI.

On 2023-08-18 09:43:08 [-0500], Yan Zhai wrote:
> > Looking at the cloudflare ppl here in the thread, I doubt they use
> > backlog but have proper NAPI so they might not need this.
> >
> Cloudflare does have backlog usage. On some veths we have to turn GRO

Oh. Okay.

> off to cope with multi-layer encapsulation, and there is also no XDP
> attached on these interfaces, thus the backlog is used. There are also
> other usage of backlog, tuntap, loopback and bpf-redirect ingress.
> Frankly speaking, making a NAPI instance "threaded" itself is not a
> concern. We have threaded NAPI running on some veth for quite a while,
> and it performs pretty well. The concern, if any, would be the
> maturity of new code. I am happy to help derisk with some lab tests
> and dogfooding if generic agreement is reached to proceed with this
> idea.

If you have threaded NAPI for veth then you wouldn't be affected by this
code. However, if you _are_ affected by this and you use veth it would
be helpful to figure out if you have problems as of net-next and if this
helps or makes it worse.

As of now Jakub isn't eager to have it and my testing/ convincing is
quite limited. If nobody else yells that something like that would be
helpful I would simply go and convince PeterZ/tglx to apply 2/2 of this
series.

> Yan

Sebastian