netdev - Re: net-shapers plan

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Message-ID: <1fc5aaa2-1c3d-48cc-99a8-523ed82b4cf9@nvidia.com>
Date: Tue, 8 Apr 2025 17:43:19 +0300
From: Carolina Jubran <cjubran@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Cosmin Ratiu <cratiu@...dia.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "horms@...nel.org" <horms@...nel.org>,
 "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
 "davem@...emloft.net" <davem@...emloft.net>, Tariq Toukan
 <tariqt@...dia.com>, Gal Pressman <gal@...dia.com>,
 "jiri@...nulli.us" <jiri@...nulli.us>, Leon Romanovsky <leonro@...dia.com>,
 "edumazet@...gle.com" <edumazet@...gle.com>,
 Saeed Mahameed <saeedm@...dia.com>, "pabeni@...hat.com" <pabeni@...hat.com>
Subject: Re: net-shapers plan



On 01/04/2025 17:50, Jakub Kicinski wrote:
> On Tue, 1 Apr 2025 11:35:56 +0300 Carolina Jubran wrote:
>>> As mentioned in Zagreb the part of HW reclassifying traffic does not
>>> make sense to me. Is this a real user scenario you have or more of
>>> an attempt to "maximize flexibility"?
>>
>> I don't believe there's a specific real-world scenario. It's really
>> about maximizing flexibility. Essentially, if a user sets things up in a
>> less-than-optimal way, the hardware can ensure that traffic is
>> classified and managed properly.
> 
> I see. If you could turn it off and leave it out, at least until clear
> user appears that'd be great. Reclassifying packets on Tx slightly goes
> against the netdev recommendation to limit any packet parsing and
> interpretation on Tx.

The hardware enforces a match between the packet’s priority and the 
scheduling queue’s configured priority. If they match, the packet is 
transmitted without further processing. If not, the hardware moves the 
Tx queue to the right scheduling queue to ensure proper traffic class 
separation.
This check is always active and cannot currently be disabled. Even when
the queue is configured with the correct priority, the hardware still 
verifies the match before sending.