net/mlx5e: Make tx_port_ts logic resilient to out-of-order CQEs
Use a map structure for associating CQEs containing port timestamping information with the appropriate skb. Track order of WQEs submitted using a FIFO. Check if the corresponding port timestamping CQEs from the lookup values in the FIFO are considered dropped due to time elapsed. Return the lookup value to a freelist after consuming the skb. Reuse the freed lookup in future WQE submission iterations. The map structure uses an integer identifier for the key and returns an skb corresponding to that identifier. Embed the integer identifier in the WQE submitted to the WQ for the transmit path when the SQ is a PTP (port timestamping) SQ. The embedded identifier can then be queried using a field in the CQE of the corresponding port timestamping CQ. In the port timestamping napi_poll context, the identifier is queried from the CQE polled from CQ and used to lookup the corresponding skb from the WQE submit path. The skb reference is removed from map and then embedded with the port HW timestamp information from the CQE and eventually consumed. The metadata freelist FIFO is an array containing integer identifiers that can be pushed and popped in the FIFO. The purpose of this structure is bookkeeping what identifier values can safely be used in a subsequent WQE submission and should not contain identifiers that have still not been reaped by processing a corresponding CQE completion on the port timestamping CQ. The ts_cqe_pending_list structure is a combination of an array and linked list. The array is pre-populated with the nodes that will be added and removed from the head of the linked list. Each node contains the unique identifier value associated with the values submitted in the WQEs and retrieved in the port timestamping CQEs. When a WQE is submitted, the node in the array corresponding to the identifier popped from the metadata freelist is added to the end of the CQE pending list and is marked as "in-use". The node is removed from the linked list under two conditions. The first condition is that the corresponding port timestamping CQE is polled in the PTP napi_poll context. The second condition is that more than a second has elapsed since the DMA timestamp value corresponding to the WQE submission. When the first condition occurs, the "in-use" bit in the linked list node is cleared, and the resources corresponding to the WQE submission are then released. The second condition, however, indicates that the port timestamping CQE will likely never be delivered. It's not impossible for the device to post a CQE after an infinite amount of time though highly improbable. In order to be resilient to this improbable case, resources related to the corresponding WQE submission are still kept, the identifier value is not returned to the freelist, and the "in-use" bit is cleared on the node to indicate that it's no longer part of the linked list of "likely to be delivered" port timestamping CQE identifiers. A count for the number of port timestamping CQEs considered highly likely to never be delivered by the device is maintained. This count gets decremented in the unlikely event a port timestamping CQE considered unlikely to ever be delivered is polled in the PTP napi_poll context. Signed-off-by:Rahul Rameshbabu <rrameshbabu@nvidia.com> Reviewed-by:
Tariq Toukan <tariqt@nvidia.com> Signed-off-by:
Saeed Mahameed <saeedm@nvidia.com>
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