Dell Emulex Family of Adapters - Manual (Page 871)

Emulex Drivers Version 10.2 for Linux User Manual P010081-01A Rev. A
3. Configuration
Network Performance Tuning
871
ethtool –K eth<N> gro off
LRO can be disabled using the –C option with the ethtool command:
ethtool -C eth<N> rx-frames 1
where eth<N> is the name of the Ethernet device you are working on (for example,
eth0).
Maximum Transmission Unit (MTU)
The Ethernet driver supports MTUs between 256 bytes and 9000 bytes. The default
MTU is set to 1500. If other elements in the network path support a larger MTU, you
can increase the MTU up to 9000 using the ifconfig command. To do this run:
ifconfig <ethN> mtu 9000
where eth<N> is the name of the Ethernet device you are working on (for example,
eth0).
Interrupt Coalescing
The Ethernet driver tries to reduce the number of interrupts by delaying the interrupts
from the adapter or CFA. This reduces CPU utilization during a high traffic rate. The
interrupt delay duration can be set to change dynamically within a range of values,
depending on the receive rate (known as Adaptive Interrupt Coalescing (AIC)), or can
be set to a constant value.
Setting the Interrupt Delay Duration to a Range of Values (AIC)
For receive interrupts, AIC is enabled by default. When AIC is enabled, the default low
limit is 0 microseconds and the default high limit is 96 microseconds. In low traffic, the
interrupt delay is set to 0 for best latency. As the number of interrupts per second
increases, the delay is increased to higher values proportional to the receive rate, up to
the default high limit of 96 microseconds. You can change the low and high limits using
ethtool. For example, to set a low limit of 8 and a high limit of 40, run
ethtool -C eth<N> rx-usecs-low 8
ethtool -C eth<N> rx-usecs-high 40
where eth<N> is the name of the Ethernet device you are working on (for example,
eth0).
For transmit interrupts, AIC is not supported.
To disable AIC and set the interrupt delay duration to a constant value, see the
following section.
Setting the Interrupt Delay Duration to a Constant Value
The interrupt delay duration can be set to a constant value for both receive and transmit
interrupts. The possible interrupt delay duration values are 0 to 96 microseconds, in 8
microsecond increments.