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

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Message-ID: <20250215140252.GP1615191@kernel.org>
Date: Sat, 15 Feb 2025 14:02:52 +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 Wed, Feb 05, 2025 at 09:09:58AM -0800, Jakub Kicinski wrote:
> On Tue, 4 Feb 2025 17:26:43 +0000 Amit Cohen wrote:
> > > > You're right, most of packets should be handled by HW, XDP is
> > > > mainly useful for telemetry.  
> > > 
> > > Why skb path is not enough?  
> > 
> > We get better packet rates using XDP, this can be useful to redirect
> > packets to a server for analysis for example.
> 
> 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.