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

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Message-ID: <20240305103530.FEVh-64E@linutronix.de>
Date: Tue, 5 Mar 2024 11:35:30 +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 11:08:35 [+0100], Paolo Abeni wrote:
> 
> Does not apply cleanly after commit 1200097fa8f0d, please rebase and
> repost. Note that we are pretty close to the net-next PR, this is at
> risk for this cycle.

will do.

> Side note: is not 110% clear to me why the admin should want to enable
> the threaded backlog for the non RT case. I read that the main
> difference would be some small perf regression, could you clarify?

I am not aware of a perf regression.
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.

> Thanks!
> 
> Paolo

Sebastian