netdev - Re: [Intel-wired-lan] [PATCH iwl-net v2 5/5] ice: Document tx_scheduling

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Message-ID: <20231007153558.GE831234@kernel.org>
Date: Sat, 7 Oct 2023 17:35:58 +0200
From: Simon Horman <horms@...nel.org>
To: Mateusz Polchlopek <mateusz.polchlopek@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	Michal Wilczynski <michal.wilczynski@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net v2 5/5] ice: Document
 tx_scheduling_layers parameter

On Fri, Oct 06, 2023 at 07:02:12AM -0400, Mateusz Polchlopek wrote:
> From: Michal Wilczynski <michal.wilczynski@...el.com>
> 
> New driver specific parameter 'tx_scheduling_layers' was introduced.
> Describe parameter in the documentation.
> 
> Signed-off-by: Michal Wilczynski <michal.wilczynski@...el.com>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
> Co-developed-by: Mateusz Polchlopek <mateusz.polchlopek@...el.com>
> Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@...el.com>

Hi,

I'm not expert here,
but this seems to cause a splat when building documentation.

.../ice.rst:70: WARNING: Unexpected indentation.
.../ice.rst:25: WARNING: Error parsing content block for the "list-table" directive: uniform two-level bullet list expected, but row 2 does not contain the same number of items as row 1 (3 vs 4).

.. list-table:: Driver-specific parameters implemented
   :widths: 5 5 5 85

   * - Name
     - Type
     - Mode
     - Description
   * - ``tx_scheduling_layers``
     - u8
     - permanent
       The ice hardware uses hierarchical scheduling for Tx with a fixed
       number of layers in the scheduling tree. Root node is representing a
       port, while all the leaves represents the queues. This way of
       configuring Tx scheduler allows features like DCB or devlink-rate
       (documented below) for fine-grained configuration how much BW is given
       to any given queue or group of queues, as scheduling parameters can be
       configured at any given layer of the tree. By default 9-layer tree
       topology was deemed best for most workloads, as it gives optimal
       performance to configurability ratio. However for some specific cases,
       this might not be the case. A great example would be sending traffic to
       queues that is not a multiple of 8. Since in 9-layer topology maximum
       number of children is limited to 8, the 9th queue has a different parent
       than the rest, and it's given more BW credits. This causes a problem
       when the system is sending traffic to 9 queues:

       | tx_queue_0_packets: 24163396
       | tx_queue_1_packets: 24164623
       | tx_queue_2_packets: 24163188
       | tx_queue_3_packets: 24163701
       | tx_queue_4_packets: 24163683
       | tx_queue_5_packets: 24164668
       | tx_queue_6_packets: 23327200
       | tx_queue_7_packets: 24163853
       | tx_queue_8_packets: 91101417 < Too much traffic is sent to 9th

       Sometimes this might be a big concern, so the idea is to empower the
       user to switch to 5-layer topology, enabling performance gains but
       sacrificing configurability for features like DCB and devlink-rate.

       This parameter gives user flexibility to choose the 5-layer transmit
       scheduler topology. After switching parameter reboot is required for
       the feature to start working.

       User could choose 9 (the default) or 5 as a value of parameter, e.g.:
       $ devlink dev param set pci/0000:16:00.0 name tx_scheduling_layers
         value 5 cmode permanent

       And verify that value has been set:
       $ devlink dev param show pci/0000:16:00.0 name tx_scheduling_layers