User Manual

Driver FeaturesRev 2.2-1.0.1
Mellanox Technologies
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4.24 pm_qos usage on ingress Packet Traffic
pm_qos API is used by mlx4_en, to enforce minimum DMA latency requirement on the system
when ingress traffic is detected. Additionally, it decreases packet loss on systems configured with
abundant power state profile when Flow Control is disabled.
The pm_qos API contains the following functions:
• pm_qos_add_request
• pm_qos_update_request
• pm_qos_remove_request
pm_qos feature is both global and static, once a request is issued, it is enforced on all CPUs and
does not change in time.
MLNX_OFED v2.2-1.0.0 provides an option to trigger a request when required and to remove it
when no longer required. It is disabled by default and can be set/unset through the ethtool priv-
flags.
For further information on how to enable/disable this feature, please refer to Table 8, “ethtool
Supported Options,” on page 133.
4.25 XOR RSS Hash Function
The device has the ability to use XOR as the RSS distribution function, instead of the default
Toplitz function.
The XOR function can be better distributed among driver's receive queues in small number of
streams, where it distributes each TCP/UDP stream to a different queue.
MLNX_OFED v2.2-1.0.0 provides an option to change the working RSS hash function from
Toplitz to XOR (and vice versa) through ethtool priv-flags.
For further information, please refer to Table 8, “ethtool Supported Options,” on page 133.