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

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Message-ID: <20250911064732.2234b9fb@kernel.org>
Date: Thu, 11 Sep 2025 06:47:32 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Mark Bloch <mbloch@...dia.com>
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 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.