netdev - Re: [PATCH net-next] Revert "net: ethtool: add support for symmetric-xor RSS hash"

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Date: Sun, 24 Dec 2023 23:03:29 +0100
From: Gerhard Engleder <gerhard@...leder-embedded.com>
To: Simon Horman <horms@...nel.org>, ahmed.zaki@...el.com
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
 edumazet@...gle.com, pabeni@...hat.com, Jeff Guo <jia.guo@...el.com>,
 Jesse Brandeburg <jesse.brandeburg@...el.com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>
Subject: Re: [PATCH net-next] Revert "net: ethtool: add support for
 symmetric-xor RSS hash"

On 24.12.23 21:54, Simon Horman wrote:
> + Jeff Guo <jia.guo@...el.com>
>    Jesse Brandeburg <jesse.brandeburg@...el.com>
>    Tony Nguyen <anthony.l.nguyen@...el.com>
> 
> On Fri, Dec 22, 2023 at 10:00:00PM +0100, Gerhard Engleder wrote:
>> This reverts commit 13e59344fb9d3c9d3acd138ae320b5b67b658694.
>>
>> The tsnep driver and at least also the macb driver implement the ethtool
>> operation set_rxnfc but not the get_rxfh operation. With this commit
>> set_rxnfc returns -EOPNOTSUPP if get_rxfh is not implemented. This renders
>> set_rxnfc unuseable for drivers without get_rxfh.
>>
>> Make set_rxfnc working again for drivers without get_rxfh by reverting
>> that commit.
>>
>> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
> 
> Hi Gerhard,
> 
> I think it would be nice to find a way forwards that resolved
> the regression without reverting the feature. But, if that doesn't work
> out, I think the following two patches need to be reverted first in
> order to avoid breaking (x86_64 allmodconfig) builds.
> 
>   352e9bf23813 ("ice: enable symmetric-xor RSS for Toeplitz hash function")
>   4a3de3fb0eb6 ("iavf: enable symmetric-xor RSS for Toeplitz hash function")

Hi Simon,

frist I thought about fixing, but then I was afraid that the rxfh check 
in ethtool_set_rxnfc() may also affect other drivers with ethtool
get_rxfh() too. I'm not an expert in that area, so I thought it is not a 
good idea to fix stuff that I don't understand and cannot test.

Taking a second look, rxfh is only checked if RXH_XFRM_SYM_XOR is set 
and this flag is introduced with the same commit. So it should be safe
to do the rxfh check only if ethtool get_rxfh() is available.