Intel Ethernet X520 10GbE Dual Port KX4 Mezz User Manual page 75

The following table contains parameters and possible values for modprobe commands:
Parameter Name Valid
Range/Settings
InterruptThrottleRate 0, 1, 3, 100-
100000 (0=off,
1=dynamic, 3=d-
dynamic con-
servative)
Default Description
3 The driver can limit the number of interrupts per second that the
adapter will generate for incoming packets. It does this by writ-
ing a value to the adapter that is based on the maximum num-
ber of interrupts that the adapter will generate per second.
Setting InterruptThrottleRate to a value greater or equal to 100
will program the adapter to send out a maximum of that many
interrupts per second, even if more packets have come in. This
reduces interrupt load on the system and can lower CPU util-
ization under heavy load, but will increase latency as packets
are not processed as quickly.
The default behavior of the driver previously assumed a static
InterruptThrottleRate value of 8000, providing a good fallback
value for all traffic types, but lacking in small packet per-
formance and latency.
The driver has two adaptive modes (setting 1 or 3) in which it
dynamically adjusts the InterruptThrottleRate value based on
the traffic that it receives. After determining the type of incoming
traffic in the last timeframe, it will adjust the Inter-
ruptThrottleRate to an appropriate value for that traffic.
The algorithm classifies the incoming traffic every interval into
classes. Once the class is determined, the InterruptThrottleRate
value is adjusted to suit that traffic type the best. There are three
classes defined: "Bulk traffic", for large amounts of packets of
normal size; "Low latency", for small amounts of traffic and/or a
significant percentage of small packets; and "Lowest latency",
for almost completely small packets or minimal traffic.
In dynamic conservative mode, the InterruptThrottleRate value
is set to 4000 for traffic that falls in class "Bulk traffic". If traffic
falls in the "Low latency" or "Lowest latency" class, the Inter-
ruptThrottleRate is increased stepwise to 20000. This default
mode is suitable for most applications.
For situations where low latency is vital such as cluster or grid
computing, the algorithm can reduce latency even more when
InterruptThrottleRate is set to mode 1. In this mode, which oper-
ates the same as mode 3, the InterruptThrottleRate will be
increased stepwise to 70000 for traffic in class "Lowest latency".
Setting InterruptThrottleRate to 0 turns off any interrupt mod-
eration and may improve small packet latency, but is generally
not suitable for bulk throughput traffic.
NOTE: InterruptThrottleRate takes precedence over the
TxAbsIntDelay and RxAbsIntDelay parameters. In other
words, minimizing the receive and/or transmit absolute
delays does not force the controller to generate more
interrupts that what the Interrupt Throttle Rate allows.