Solarflare Solarflare XtremeScale series, User Manual, Page: 111 / 400

Solarflare Server Adapter User Guide
Solarflare Adapters on Linux
Issue 20 © Solarflare Communications 2017 104
Latency will be affected by the type of physical medium used: 10GBase ‐ T, twinaxial
(direct ‐ attach), fiber or KX4. This is because the physical media interface chip (PHY)
used on the adapter can introduce additional latency. Likewise, latency can also be
affected by the type of SFP/SFP+/QSFP module fitted.
In addition, you may need to consider other issues influencing performance, such as
application settings, server motherboard chipset, CPU speed, cache size, RAM size,
additional software installed on the system, such as a firewall, and the specification
and configuration of the LAN. Consideration of such issues is not within the scope of
this guide.
Tuning settings
Port mode
The selected port mode for SFN7000 and SFN8000 series adapters should
correspond to the speed and number of connectors in use, after using any splitter
cables. If a restricted set of connectors is configured, the driver can then transfer
resources from the unused connectors to those configured, potentially improving
performance.
Adapter MTU (Maximum Transmission Unit)
The default MTU of 1500 bytes ensures that the adapter is compatible with legacy
10/100Mbps Ethernet endpoints. However if a larger MTU is used, adapter
throughput and CPU utilization can be improved. CPU utilization is improved,
because it takes fewer packets to send and receive the same amount of data.
Solarflare adapters support an MTU of up to 9216 bytes (this does not include the
Ethernet preamble or frame ‐ CRC).
Since the MTU should ideally be matched across all endpoints in the same LAN
(VLAN), and since the LAN switch infrastructure must be able to forward such
packets, the decision to deploy a larger than default MTU requires careful
consideration. It is recommended that experimentation with MTU be done in a
controlled test environment.
The MTU is changed dynamically using ifconfig, where
ethX
is the interface name
and
<size>
is the MTU size in bytes:
# /sbin/ifconfig <ethX> mtu <size>
Verification of the MTU setting may be performed by running
ifconfig
with no
options and checking the MTU value associated with the interface. The change in
MTU size can be made to persist across reboots by editing the file
/etc/
sysconfig/network ‐ scripts/ifcfg ‐ ethX
and adding
MTU=<mtu>
on a new line.