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Solarflare Server Adapter User Guide
Solarflare Adapters on FreeBSD
Issue 20 © Solarflare Communications 2017 311
To set
<m>
RSS Receive queues, where
sfxge<n>
is the interface name:
kenv hw.sfxge.<n>.max_rss_channels=<m>

kldload /boot/modules/sfxge.ko
Sometimes, it can be desirable to disable RSS when running single stream
applications, since all interface processing may benefit from taking place on a single
CPU. To do so, set a single RSS Receive queue:
kenv hw.sfxge.<n>.max_rss_channels=1

kldload /boot/modules/sfxge.ko
The change in RSS Receive queues can be made to persist across reboots by editing
the file
/boot/loader.conf
and adding
hw.sfxge.<n>.max_rss_channels=<m>
on a new line.
If no MSI/MSI ‐ X interrupts are available then the driver will fall ‐ back to use a single
legacy interrupt. RSS will be unavailable for that port.
NOTE: RSS also works for UDP packets. For UDP traffic the Solarflare adapter will
select the Receive CPU based on IP source and destination addresses. Solarflare
adapters support IPv4 and IPv6 RSS.
Other Considerations
PCI Express Lane Configurations
The PCI Express (PCIe) interface used to connect the adapter to the server can
function at different speeds and widths. This is independent of the physical slot size
used to connect the adapter. The possible widths are multiples x1, x2, x4, x8 and x16
lanes of (2.5Gbps for PCIe Gen 1, 5.0 Gbps for PCIe Gen 2 and 8.0Gbps for PCIe Gen
3) in each direction. Solarflare adapters are designed for x8 or x16 lane operation .
On some server motherboards, choice of PCIe slot is important. This is because
some slots (including those that are physically x8 or x16 lanes) may only electrically
support x4 lanes. In x4 lane slots, Solarflare PCIe adapters will continue to operate,
but not at full speed. The Solarflare driver will warn if it detects that the adapter is
plugged into a PCIe slot which electrically has fewer than x8 lanes.
Solarflare SFN5000 and SFN6000 series adapters require a PCIe Gen 2 x8 slot for
optimal operation. Solarflare SFN7000 and SFN8000 series adapters require a PCIe
Gen 3 x8 or x16 slot for optimal performance. The Solarflare driver will warn if it
detects that the adapter is placed in a sub ‐ optimal slot.
In addition, the latency of communications between the host CPUs, system memory
and the Solarflare PCIe adapter may be PCIe slot dependent. Some slots may be
“closer” to the CPU, and therefore have lower latency and higher throughput. If
possible, install the adapter in a slot which is local to the desired NUMA node
Please consult your server user guide for more information.