LAN Configuration and Management Manual

SCF Commands for the SLSA Subsystem
LAN Configuration and Management Manual—520469-012
4-26
ADD LIF Command
DATAFORWARDUNIT of MICROSECONDS is specified for non-G4SA adapter
types.

DATAFORWARDCOUNT and DATAFORWARDTIME are meaningful only when the
specified PIF is a part of an Ethernet 4 ServerNet adapter (E4SA), Fast Ethernet
ServerNet adapter (FESA), Gigabit Ethernet ServerNet adapter (GESA), Gigabit
Ethernet 4-port ServerNet Adapter (G4SA), or Token Ring ServerNet adapter
(TRSA).
Considerations When Using the DFC, DFM, and DFT Parameters
The Data Forward Count (DFC) and Data Forward Time (DFT) parameters are used to
control the frame-forwarding behavior of the controller when sending incoming data to
the host changing the frame forwarding behavior reduces the interrupt load on the host
processor while retaining an acceptable forwarding delay.
Data frames are forwarded when the arriving frame count equals the configured DFC
value or the configured DFT time has elapsed.
The challenge of configuring DFC and DFT is allowing for different data-traffic profiles.
Normally DFC would be set to a high value to reduce the interrupt load on the host for
a high-volume, streaming data profile, but this configuration may cause unacceptable
forwarding delays for single-frame data traffic. Conversely, a DFC setting of 1 would
provide immediate frame-forwarding but also incur the highest host-interrupt overhead
because a host interrupt would be generated for every frame.
The Data Forward Mode (DFM) parameter provides a solution for configuring
DFC/DFT for different traffic profiles. DFM can be set either to MANUAL or ADAPTIVE.
If DFM is configured as MANUAL, DFC and DFT operate in the traditional manner as
described above. If DFM is configured as ADAPTIVE, the frame-forwarding behavior
adapts as the traffic profile changes.
In adaptive mode, DFC and DFT are configurable but interact differently. DFT
represents the maximum time allowed before a group of frames are forwarded to the
host. The DFC value, however, is dynamically adjusted based on the traffic pattern.
Initially, DFC starts with a value of 1. This means that a data frame is forwarded to the
host immediately upon reception providing the lowest forwarding delay. If frames
continue to arrive intermittently, they are forwarded immediately. If the traffic pattern
changes and a continuous frame stream is present, the DFC value increases, causing
the interrupt load on the host to be reduced. The DFC stops increasing when it reaches
the configured DFC value. The dynamic DFC value remains at the maximum as long
as frames are forwarded based on DFC. If frame groups begin to time out and are
forwarded based on the DFT value, the DFC is dynamically reduced to the point where
frames are once again forwarded based on DFC. If the traffic pattern reverts to
intermittent frame arrival, DFC returns to 1 providing minimal forwarding delay.
During some periods the traffic pattern may be changing so that data frames are
forwarded based on DFT but, ideally, in adaptive mode, frames are mostly forwarded
based on DFC, providing responsive forwarding characteristics along with a reduced
host-interrupt load.