netdev - Re: [net 0/2] rxfh with custom RSS fixes

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Date: Mon, 24 Jul 2023 15:08:15 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Edward Cree <ecree.xilinx@...il.com>
Cc: Joe Damato <jdamato@...tly.com>, netdev@...r.kernel.org,
 saeedm@...dia.com, tariqt@...dia.com, ecree@...arflare.com, andrew@...n.ch,
 davem@...emloft.net, leon@...nel.org, pabeni@...hat.com,
 bhutchings@...arflare.com, arnd@...db.de, linux-kernel@...r.kernel.org
Subject: Re: [net 0/2] rxfh with custom RSS fixes

On Mon, 24 Jul 2023 20:27:43 +0100 Edward Cree wrote:
> On 23/07/2023 16:06, Joe Damato wrote:
> > Greetings:
> > 
> > While attempting to get the RX flow hash key for a custom RSS context on
> > my mlx5 NIC, I got an error:
> > 
> > $ sudo ethtool -u eth1 rx-flow-hash tcp4 context 1
> > Cannot get RX network flow hashing options: Invalid argument
> > 
> > I dug into this a bit and noticed two things:
> > 
> > 1. ETHTOOL_GRXFH supports custom RSS contexts, but ETHTOOL_SRXFH does
> > not. I moved the copy logic out of ETHTOOL_GRXFH and into a helper so
> > that both ETHTOOL_{G,S}RXFH now call it, which fixes ETHTOOL_SRXFH. This
> > is patch 1/2.  
> 
> As I see it, this is a new feature, not a fix, so belongs on net-next.
> (No existing driver accepts FLOW_RSS in ETHTOOL_SRXFH's cmd->flow_type,
>  which is just as well as if they did this would be a uABI break.)
> 
> Going forward, ETHTOOL_SRXFH will hopefully be integrated into the new
>  RSS context kAPI I'm working on[1], so that we can have a new netlink
>  uAPI for RSS configuration that's all in one place instead of the
>  piecemeal-grown ethtool API with its backwards-compatible hacks.
> But that will take a while, so I think this should go in even though
>  it's technically an extension to legacy ethtool; it was part of the
>  documented uAPI and userland implements it, it just never got
>  implemented on the kernel side (because the initial driver with
>  context support, sfc, didn't support SRXFH).

What's the status on your work? Are you planning to split the RSS
config from ethtool or am I reading too much into what you said?

It'd be great to push the uAPI extensions back and make them
netlink-only, but we can't make Joe wait if it takes a long time
to finish up the basic conversion :(