netdev - Re: [PATCH net-next 10/11] ethtool: rss: support setting flow hashing fields

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Message-ID: <7bfc8766-0f6f-4309-984e-24ef86f5c8e3@nvidia.com>
Date: Tue, 15 Jul 2025 13:27:51 +0300
From: Gal Pressman <gal@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, andrew+netdev@...n.ch, horms@...nel.org,
 donald.hunter@...il.com, shuah@...nel.org, kory.maincent@...tlin.com,
 maxime.chevallier@...tlin.com, sdf@...ichev.me, ecree.xilinx@...il.com
Subject: Re: [PATCH net-next 10/11] ethtool: rss: support setting flow hashing
 fields

On 14/07/2025 19:29, Jakub Kicinski wrote:
> On Sun, 13 Jul 2025 14:12:33 +0300 Gal Pressman wrote:
>> On 11/07/2025 4:53, Jakub Kicinski wrote:
>>> Add support for ETHTOOL_SRXFH (setting hashing fields) in RSS_SET.
>>>
>>> The tricky part is dealing with symmetric hashing, user can change
>>> the hashing fields and symmetric hash in one request. Since fields
>>> and hash function config are separate driver callback changes to
>>> the two are not atomic. Keep things simple and validate the settings
>>> against both pre- and post- change ones. Meaning that we will reject
>>> the config request if user tries to correct the flow fields and set
>>> input_xfrm in one request, or disables input_xfrm and makes flow
>>> fields non-symmetric.  
>>
>> How is it different than what we have in ioctl?
> 
> Because:
> 
>   user can change the hashing fields and symmetric hash in one request
> 
> IOCTL has two separate calls for this so there's no way to even try
> to change both at once. I'll add "unlike IOCTL which has separate
> calls" ?

So it's different because you can use netlink directly to change both,
but from userspace ethtool perspective there's no difference, right?
It's still two commands.

Makes sense, thanks for the explanation.

> 
>>> We can adjust it later if there's a real need. Starting simple feels
>>> right, and potentially partially applying the settings isn't nice,
>>> either.
>>>
>>> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
>>> ---
>>>  static void
>>>  rss_set_ctx_update(struct ethtool_rxfh_context *ctx, struct nlattr **tb,
>>>  		   struct rss_reply_data *data, struct ethtool_rxfh_param *rxfh)
>>> @@ -673,11 +767,11 @@ ethnl_rss_set(struct ethnl_req_info *req_info, struct genl_info *info)
>>>  	struct rss_req_info *request = RSS_REQINFO(req_info);
>>>  	struct ethtool_rxfh_context *ctx = NULL;
>>>  	struct net_device *dev = req_info->dev;
>>> +	bool mod = false, fields_mod = false;  
>>
>> Why not use mod?
> 
> Because it's a difference driver-facing op.

Why do we need to differentiate where the mod originated? We have a
single return value.