From: Michal Wilczynski <michal.wilczynski@xxxxxxxxx>
New driver specific parameter 'tx_scheduling_layers' was introduced.
Describe parameter in the documentation.
Signed-off-by: Michal Wilczynski <michal.wilczynski@xxxxxxxxx>
Acked-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@xxxxxxxxx>
Co-developed-by: Mateusz Polchlopek <mateusz.polchlopek@xxxxxxxxx>
Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@xxxxxxxxx>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
---
Documentation/networking/devlink/ice.rst | 47 ++++++++++++++++++++++++
1 file changed, 47 insertions(+)
diff --git a/Documentation/networking/devlink/ice.rst b/Documentation/networking/devlink/ice.rst
index 7f30ebd5debb..830c04354222 100644
--- a/Documentation/networking/devlink/ice.rst
+++ b/Documentation/networking/devlink/ice.rst
@@ -21,6 +21,53 @@ Parameters
* - ``enable_iwarp``
- runtime
- mutually exclusive with ``enable_roce``
+ * - ``tx_scheduling_layers``
+ - permanent
+ - The ice hardware uses hierarchical scheduling for Tx with a fixed
+ number of layers in the scheduling tree. Each of them are decision
+ points. Root node represents a port, while all the leaves represent
+ the queues. This way of configuring the Tx scheduler allows features
+ like DCB or devlink-rate (documented below) to configure how much
+ bandwidth is given to any given queue or group of queues, enabling
+ fine-grained control because scheduling parameters can be configured
+ at any given layer of the tree.
+
+ The default 9-layer tree topology was deemed best for most workloads,
+ as it gives an optimal ratio of performance to configurability. However,
+ for some specific cases, this 9-layer topology might not be desired.
+ One example would be sending traffic to queues that are not a multiple
+ of 8. Because the maximum radix is limited to 8 in 9-layer topology,
+ the 9th queue has a different parent than the rest, and it's given
+ more bandwidth 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 from 9th
+
+ To address this need, you can switch to a 5-layer topology, which
+ changes the maximum topology radix to 512. With this enhancement,
+ the performance characteristic is equal as all queues can be assigned
+ to the same parent in the tree. The obvious drawback of this solution
+ is a lower configuration depth of the tree.
+
+ Use the ``tx_scheduling_layer`` parameter with the devlink command
+ to change the transmit scheduler topology. To use 5-layer topology,
+ use a value of 5. For example:
+ $ devlink dev param set pci/0000:16:00.0 name tx_scheduling_layers
+ value 5 cmode permanent
+ Use a value of 9 to set it back to the default value.
+
+ You must do PCI slot powercycle for the selected topology to take effect.
+
+ To verify that value has been set:
+ $ devlink dev param show pci/0000:16:00.0 name tx_scheduling_layers
Info versions
=============
--
2.41.0
