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Message-ID: <e9e362e3a571bc32afb344cf35b54395e741de90.camel@redhat.com>
Subject: Re: [PATCH net-next v2] net/core: add optional threading for
 backlog processing
From:   Paolo Abeni <pabeni@redhat.com>
To:     Jakub Kicinski <kuba@kernel.org>, Felix Fietkau <nbd@nbd.name>
Cc:     netdev@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Thu, 30 Mar 2023 13:01:31 +0200
In-Reply-To: <20230328161642.3d2f101c@kernel.org>
References: <20230328195925.94495-1-nbd@nbd.name>
         <20230328161642.3d2f101c@kernel.org>
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On Tue, 2023-03-28 at 16:16 -0700, Jakub Kicinski wrote:
> On Tue, 28 Mar 2023 21:59:25 +0200 Felix Fietkau wrote:
> > When dealing with few flows or an imbalance on CPU utilization, static =
RPS
> > CPU assignment can be too inflexible. Add support for enabling threaded=
 NAPI
> > for backlog processing in order to allow the scheduler to better balanc=
e
> > processing. This helps better spread the load across idle CPUs.
>=20
> Can you share some numbers vs a system where RPS only spreads to=20
> the cores which are not running NAPI?
>=20
> IMHO you're putting a lot of faith in the scheduler and you need=20
> to show that it actually does what you say it will do.

I have the same feeling. From your description I think some gain is
possible if there are no other processes running except
ksoftirq/rps/threaded napi.=C2=A0

I guess that the above is expect average state for a small s/w router,
but if/when routing daemon/igmp proxy/local web server kicks-in you
should notice a measurable higher latency (compared to plain RPS in the
same scenario)???

Cheers,

Paolo