Intel Ethernet X520 10GbE Dual Port KX4 Mezz User Manual page 66

Parameter Name Valid
Range/Settings
Default Description
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
InterruptThrottleRate 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 operates the same as mode 3, the Inter-
ruptThrottleRate will be increased stepwise to 70000 for
traffic in class "Lowest latency".
In simplified mode the interrupt rate is based on the ratio of
tx and rx traffic. If the bytes-per-second rates are approx-
imately equal, the interrupt rate will drop as low as 2000
interrupts per second. If the traffic is mostly transmit or mostly
receive, the interrupt rate could be as high as 8000.
Setting InterruptThrottleRate to 0 turns off any interrupt mod-
eration and may improve small packet latency, but is gen-
erally not suitable for bulk throughput traffic.
NOTE: When e1000e is loaded with default settings
and multiple adapters are in use simultaneously, the
CPU utilization may increase non-linearly. In order to
limit the CPU utilization without impacting the overall
throughput, load the driver as follows:
modprobe e1000e.o Inter-
ruptThrottleRate-
e=3000,3000,3000
This sets the InterruptThrottleRate to 3000 inter-
rupts/sec for the first, second, and third instances of
the driver. The range of 2000 to 3000 interrupts per
second works on a majority of systems and is a good
starting point, but the optimal value will be platform-
specific. If CPU utilization is not a concern, use RX_
POLLING (NAPI) and default driver settings.
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 gen-
erate more interrupts than what the Interrupt Throttle
Rate allows.