netdev - Re: [PATCH net-next] net: ethtool: Don't check if RSS context exists in case of context 0

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Message-ID: <Z79Shk7-2HJM_3ec@LQ3V64L9R2>
Date: Wed, 26 Feb 2025 12:42:30 -0500
From: Joe Damato <jdamato@...tly.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Gal Pressman <gal@...dia.com>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>, netdev@...r.kernel.org,
	Andrew Lunn <andrew@...n.ch>, Simon Horman <horms@...nel.org>,
	Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH net-next] net: ethtool: Don't check if RSS context exists
 in case of context 0

On Tue, Feb 25, 2025 at 05:01:28PM -0800, Jakub Kicinski wrote:
> On Tue, 25 Feb 2025 09:13:48 +0200 Gal Pressman wrote:
> > Context 0 (default context) always exists, there is no need to check
> > whether it exists or not when adding a flow steering rule.
> > 
> > The existing check fails when creating a flow steering rule for context
> > 0 as it is not stored in the rss_ctx xarray.
> 
> But what is the use case for redirecting to context 0?

I think Gal's example is a good one and there could be users who are
already directing flows to context 0 and so, as Gal mentioned, this
might be a breakage? Not sure.

I'll admit that I'd typically create a custom context and then set
ntuple filters to direct traffic for those contexts (letting all the
'other' traffic land in the default context 0), so I can understand
Jakub's argument, as well.

I'm probably wrong because I'm not a python programmer, but IMHO
it'd be a nice for the python RSS tests to be updated to cover this
case (whichever way it goes). It seemed to me from a quick read
(again, likely wrong) that it wasn't covered and could lead to
confusion like this in the future?