netdev - Re: [PATCH net-next 00/12] mlxsw: Preparations for XDP support

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Message-ID: <20250216092646.GY1615191@kernel.org>
Date: Sun, 16 Feb 2025 09:26:46 +0000
From: Simon Horman <horms@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Amit Cohen <amcohen@...dia.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Petr Machata <petrm@...dia.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Network Development <netdev@...r.kernel.org>,
	Ido Schimmel <idosch@...dia.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	bpf <bpf@...r.kernel.org>, mlxsw <mlxsw@...dia.com>
Subject: Re: [PATCH net-next 00/12] mlxsw: Preparations for XDP support

On Sat, Feb 15, 2025 at 08:10:43AM -0800, Jakub Kicinski wrote:
> On Sat, 15 Feb 2025 14:02:52 +0000 Simon Horman wrote:
> > > TBH I also feel a little ambivalent about adding advanced software
> > > features to mlxsw. You have a dummy device off which you hang the NAPIs,
> > > the page pools, and now the RXQ objects. That already works poorly with
> > > our APIs. How are you going to handle the XDP side? Program per port, 
> > > I hope? But the basic fact remains that only fallback traffic goes thru
> > > the XDP program which is not the normal Linux model, routing is after
> > > XDP.
> > > 
> > > On one hand it'd be great if upstream switch drivers could benefit from
> > > the advanced features. On the other the HW is clearly not capable of
> > > delivering in line with how NICs work, so we're signing up for a stream
> > > of corner cases, bugs and incompatibility. Dunno.  
> > 
> > FWIIW, I do think that as this driver is actively maintained by the vendor,
> > and this is a grey zone, it is reasonable to allow the vendor to decide if
> > they want the burden of this complexity to gain some performance.
> 
> Yes, I left this series in PW for an extra couple of days expecting
> a discussion but I suppose my email was taken as a final judgment.

Yes, I was trying to spur that discussion.

> The object separation can be faked more accurately, and analyzed
> (in the cover letter) to give us more confidence that the divergence
> won't create problems.
> 
> The "actively maintained" part is true and very much appreciated, but
> it's both something that may easily change, and is hard to objectively
> adjudicate. Reporting results to the upstream CI would be much more
> objective and hopefully easier to maintain, were the folks supporting
> mlxsw to "join a startup", or otherwise disengage.

A good point. Things can change. And that may leave upstream maintainers
caring the can.