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

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Date:   Mon, 16 Oct 2023 11:53:21 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     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 <hawk@...nel.org>
Subject: Re: [PATCH net-next 0/2] net: Use SMP threads for backlog NAPI (or
 optional).

Sorry, getting back that late, I was traveling the last two weeks…

On 2023-10-09 18:09:37 [-0700], Jakub Kicinski wrote:
> On Sat, 7 Oct 2023 17:59:57 +0200 Sebastian Andrzej Siewior wrote:
> > Apologies if I misunderstood. You said to make it optional which I did
> > with the static key in the second patch of this series. The first patch
> > is indeed not what we talked about I just to show what it would look
> > like now that there is no "delay" for backlog-NAPI on the local CPU.
> > 
> > If the optional part is okay then I can repost only that patch against
> > current net-next.
> 
> Do we have reason to believe nobody uses RPS?

Not sure what you relate to. I would assume that RPS is used in general
on actual devices and not on loopback where backlog is used. But it is
just an assumption.
The performance drop, which I observed with RPS and stress-ng --udp, is
within the same range with threads and IPIs (based on memory). I can
re-run the test and provide actual numbers if you want.

Sebastian