netdev - Re: [net 06/10] net/mlx5: RSS, Block changing channels number when RXFH is configured

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Date: Thu, 28 Mar 2024 22:31:49 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Saeed Mahameed <saeed@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, Paolo Abeni
 <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>, Saeed Mahameed
 <saeedm@...dia.com>, netdev@...r.kernel.org, Tariq Toukan
 <tariqt@...dia.com>, Gal Pressman <gal@...dia.com>, Leon Romanovsky
 <leonro@...dia.com>, Carolina Jubran <cjubran@...dia.com>
Subject: Re: [net 06/10] net/mlx5: RSS, Block changing channels number when
 RXFH is configured

On Tue, 26 Mar 2024 07:46:42 -0700 Saeed Mahameed wrote:
> Changing the channels number after configuring the receive
> flow hash indirection table may alter the RSS table size.
> The previous configuration may no longer be compatible with
> the new receive flow hash indirection table.
> 
> Block changing the channels number when RXFH is configured.

Do I understand correctly that this will block all set_channels
calls after indir table changes? This may be a little too risky
for a fix. Perhaps okay for net-next, but not a fix.

I'd think that setting indir table and then increasing the number 
of channels is a pretty legit maneuver, or even best practice
to allocate a queue outside of RSS.

Is it possible to make a narrower change, only rejecting the truly
problematic transitions?