netdev - Re: [PATCH v3 net-next 2/4] net: Allow to use SMP threads for backlog NAPI.

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Message-ID: <20240305105218.EXitUftO@linutronix.de>
Date: Tue, 5 Mar 2024 11:52:18 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wander Lairson Costa <wander@...hat.com>,
	Yan Zhai <yan@...udflare.com>
Subject: Re: [PATCH v3 net-next 2/4] net: Allow to use SMP threads for
 backlog NAPI.

On 2024-03-05 11:44:06 [+0100], Paolo Abeni wrote:
> > I am not aware of a perf regression.
> 
> I probably inferred too much from the udp lookback case.

Yes. This was real and is gone now :)

> > Jakub was worried about a possible regression with this and while asking
> > nobody came up with an actual use case where this is used. So it is as
> > he suggested, optional for everyone but forced-enabled for RT where it
> > is required.
> > I had RH benchmarking this and based on their 25Gbe and 50Gbe NICs and
> > the results look good. If anything it looked a bit better with this on
> > the 50Gbe NICs but since those NICs have RSS…
> > 
> > I have this default off so that nobody complains and yet has to
> > possibility to test and see if it leads to a problem. If not, we could
> > enable it by default and after a few cycles and then remove the IPI code
> > a few cycles later with absent complains.
> 
> I think this late in the cycle is better to keep backlog threads off by
> default.

Sure.

> Thanks,
> 
> Paolo

Seastian