Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
MIME-Version: 1.0
References: <20230814093528.117342-1-bigeasy@linutronix.de>
 <20230814112421.5a2fa4f6@kernel.org> <20230817131612.M_wwTr7m@linutronix.de>
 <CAO3-Pbo7q6Y-xzP=3f58Y3MyWT2Vruy6UhKiam2=mAKArxgMag@mail.gmail.com> <20230818145734.OgLYhPh1@linutronix.de>
In-Reply-To: <20230818145734.OgLYhPh1@linutronix.de>
From:   Yan Zhai <yan@cloudflare.com>
Date:   Fri, 18 Aug 2023 11:56:59 -0500
Message-ID: <CAO3-Pbr4u8+UsmmN+kHF4Yv+-THAnUxSgROLyK3Tvjb9W5gHZQ@mail.gmail.com>
Subject: Re: [RFC PATCH net-next 0/2] net: Use SMP threads for backlog NAPI.
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Jakub Kicinski <kuba@kernel.org>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Wander Lairson Costa <wander@redhat.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Aug 18, 2023 at 9:57=E2=80=AFAM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> 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.
>
yes we are still impacted on non-NAPI veths and other scenarios. But
net-next sounds good, still plenty of time to evaluate if it has any
negative impact.

Yan

> 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