netdev - Re: [PATCH ethtool-next] rxclass: Make output for RSS context action explicit

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Message-ID: <ea2eb6ca-0f79-26a7-0e61-6450b7f5a9a2@gmail.com>
Date: Fri, 8 Nov 2024 19:56:41 +0000
From: Edward Cree <ecree.xilinx@...il.com>
To: Daniel Xu <dxu@...uu.xyz>, davem@...emloft.net, mkubecek@...e.cz
Cc: kuba@...nel.org, martin.lau@...ux.dev, netdev@...r.kernel.org,
 kernel-team@...a.com
Subject: Re: [PATCH ethtool-next] rxclass: Make output for RSS context action
 explicit

On 08/11/2024 19:32, Daniel Xu wrote:
> Currently, if the action for an ntuple rule is to redirect to an RSS
> context, the RSS context is printed as an attribute. At the same time,
> a wrong action is printed. For example:
> 
>     # ethtool -X eth0 hfunc toeplitz context new start 24 equal 8
>     New RSS context is 1
> 
>     # ethtool -N eth0 flow-type ip6 dst-ip $IP6 context 1
>     Added rule with ID 0
> 
>     # ethtool -n eth0 rule 0
>     Filter: 0
>             Rule Type: Raw IPv6
>             Src IP addr: :: mask: ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
>             Dest IP addr: <redacted> mask: ::
>             Traffic Class: 0x0 mask: 0xff
>             Protocol: 0 mask: 0xff
>             L4 bytes: 0x0 mask: 0xffffffff
>             RSS Context ID: 1
>             Action: Direct to queue 0
> 
> This is wrong and misleading. Fix by treating RSS context as a explicit
> action. The new output looks like this:
> 
>     # ./ethtool -n eth0 rule 0
>     Filter: 0
>             Rule Type: Raw IPv6
>             Src IP addr: :: mask: ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
>             Dest IP addr: <redacted> mask: ::
>             Traffic Class: 0x0 mask: 0xff
>             Protocol: 0 mask: 0xff
>             L4 bytes: 0x0 mask: 0xffffffff
>             Action: Direct to RSS context id 1
> 
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>

I believe this patch is incorrect.  My understanding is that on
 packet reception, the integer returned from the RSS indirection
 table is *added* to the queue number from the ntuple rule, so
 that for instance the same indirection table can be used for one
 rule distributing packets over queues 0-3 and for another rule
 distributing a different subset of packets over queues 4-7.
I'm not sure if this behaviour is documented anywhere, and
 different NICs may have different interpretations, but this is
 how sfc ef10 behaves.

-Ed