netdev - Re: [PATCH net V2 10/11] net/mlx5e: Update and set Xon/Xoff upon port speed set

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Message-ID: <fdd4a537-8fa3-42ae-bfab-80c0dc32a7c2@nvidia.com>
Date: Thu, 11 Sep 2025 17:25:22 +0300
From: Mark Bloch <mbloch@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Tariq Toukan <tariqt@...dia.com>,
 Leon Romanovsky <leon@...nel.org>, Saeed Mahameed <saeedm@...dia.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Gal Pressman <gal@...dia.com>, linux-rdma@...r.kernel.org,
 Alexei Lazar <alazar@...dia.com>
Subject: Re: [PATCH net V2 10/11] net/mlx5e: Update and set Xon/Xoff upon port
 speed set

On 11/09/2025 16:47, Jakub Kicinski wrote:
> On Wed, 10 Sep 2025 17:00:11 -0700 Jakub Kicinski wrote:
>> On Mon, 25 Aug 2025 17:34:33 +0300 Mark Bloch wrote:
>>> Xon/Xoff sizes are derived from calculations that include
>>> the port speed.
>>> These settings need to be updated and applied whenever the
>>> port speed is changed.
>>> The port speed is typically set after the physical link goes down
>>> and is negotiated as part of the link-up process between the two
>>> connected interfaces.
>>> Xon/Xoff parameters being updated at the point where the new
>>> negotiated speed is established.  
>>
>> Hi, this is breaking dual host CX7 w/ 28.45.1300 (but I think most
>> older FW versions, too). Looks like the host is not receiving any
>> mcast (ping within a subnet doesn't work because the host receives
>> no ndisc), and most traffic slows down to a trickle.
>> Lost of rx_prio0_buf_discard increments.
>>
>> Please TAL ASAP, this change went to LTS last week.
> 
> Any news on this? I heard that it also breaks DCB/QoS configuration
> on 6.12.45 LTS.

Hi Jakub,

We are looking into this, once we have anything I'll update.
Just to make sure, reverting this is one commit solves the
issue you are seeing?

Mark