netdev - Re: [PATCH iwl-net v3 3/3] ice: fix rebuilding the Tx scheduler tree for large queue counts

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Message-ID: <20250515114644.GW3339421@horms.kernel.org>
Date: Thu, 15 May 2025 12:46:44 +0100
From: Simon Horman <horms@...nel.org>
To: Michal Kubiak <michal.kubiak@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, maciej.fijalkowski@...el.com,
	aleksander.lobakin@...el.com, przemyslaw.kitszel@...el.com,
	dawid.osuchowski@...ux.intel.com, jacob.e.keller@...el.com,
	jbrandeburg@...udflare.com, netdev@...r.kernel.org
Subject: Re: [PATCH iwl-net v3 3/3] ice: fix rebuilding the Tx scheduler tree
 for large queue counts

On Tue, May 13, 2025 at 12:55:29PM +0200, Michal Kubiak wrote:
> The current implementation of the Tx scheduler allows the tree to be
> rebuilt as the user adds more Tx queues to the VSI. In such a case,
> additional child nodes are added to the tree to support the new number
> of queues.
> Unfortunately, this algorithm does not take into account that the limit
> of the VSI support node may be exceeded, so an additional node in the
> VSI layer may be required to handle all the requested queues.
> 
> Such a scenario occurs when adding XDP Tx queues on machines with many
> CPUs. Although the driver still respects the queue limit returned by
> the FW, the Tx scheduler was unable to add those queues to its tree
> and returned one of the errors below.
> 
> Such a scenario occurs when adding XDP Tx queues on machines with many
> CPUs (e.g. at least 321 CPUs, if there is already 128 Tx/Rx queue pairs).
> Although the driver still respects the queue limit returned by the FW,
> the Tx scheduler was unable to add those queues to its tree and returned
> the following errors:
> 
>      Failed VSI LAN queue config for XDP, error: -5
> or:
>      Failed to set LAN Tx queue context, error: -22
> 
> Fix this problem by extending the tree rebuild algorithm to check if the
> current VSI node can support the requested number of queues. If it
> cannot, create as many additional VSI support nodes as necessary to
> handle all the required Tx queues. Symmetrically, adjust the VSI node
> removal algorithm to remove all nodes associated with the given VSI.
> Also, make the search for the next free VSI node more restrictive. That is,
> add queue group nodes only to the VSI support nodes that have a matching
> VSI handle.
> Finally, fix the comment describing the tree update algorithm to better
> reflect the current scenario.
> 
> Fixes: b0153fdd7e8a ("ice: update VSI config dynamically")
> Reviewed-by: Dawid Osuchowski <dawid.osuchowski@...ux.intel.com>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
> Signed-off-by: Michal Kubiak <michal.kubiak@...el.com>

Reviewed-by: Simon Horman <horms@...nel.org>