+- ``tx_db_nc`` parameter [int]
+
+ The rdma core library can map doorbell register in two ways, depending on the
+ environment variable "MLX5_SHUT_UP_BF":
+
+ - As regular cached memory (usually with write combining attribute), if the
+ variable is either missing or set to zero.
+ - As non-cached memory, if the variable is present and set to not "0" value.
+
+ The type of mapping may slightly affect the Tx performance, the optimal choice
+ is strongly relied on the host architecture and should be deduced practically.
+
+ If ``tx_db_nc`` is set to zero, the doorbell is forced to be mapped to regular
+ memory (with write combining), the PMD will perform the extra write memory barrier
+ after writing to doorbell, it might increase the needed CPU clocks per packet
+ to send, but latency might be improved.
+
+ If ``tx_db_nc`` is set to one, the doorbell is forced to be mapped to non
+ cached memory, the PMD will not perform the extra write memory barrier
+ after writing to doorbell, on some architectures it might improve the
+ performance.
+
+ If ``tx_db_nc`` is set to two, the doorbell is forced to be mapped to regular
+ memory, the PMD will use heuristics to decide whether write memory barrier
+ should be performed. For bursts with size multiple of recommended one (64 pkts)
+ it is supposed the next burst is coming and no need to issue the extra memory
+ barrier (it is supposed to be issued in the next coming burst, at least after
+ descriptor writing). It might increase latency (on some hosts till next
+ packets transmit) and should be used with care.
+
+ If ``tx_db_nc`` is omitted or set to zero, the preset (if any) environment
+ variable "MLX5_SHUT_UP_BF" value is used. If there is no "MLX5_SHUT_UP_BF",
+ the default ``tx_db_nc`` value is zero for ARM64 hosts and one for others.
+
+- ``tx_pp`` parameter [int]
+
+ If a nonzero value is specified the driver creates all necessary internal
+ objects to provide accurate packet send scheduling on mbuf timestamps.
+ The positive value specifies the scheduling granularity in nanoseconds,
+ the packet send will be accurate up to specified digits. The allowed range is
+ from 500 to 1 million of nanoseconds. The negative value specifies the module
+ of granularity and engages the special test mode the check the schedule rate.
+ By default (if the ``tx_pp`` is not specified) send scheduling on timestamps
+ feature is disabled.
+
+- ``tx_skew`` parameter [int]
+
+ The parameter adjusts the send packet scheduling on timestamps and represents
+ the average delay between beginning of the transmitting descriptor processing
+ by the hardware and appearance of actual packet data on the wire. The value
+ should be provided in nanoseconds and is valid only if ``tx_pp`` parameter is
+ specified. The default value is zero.
+