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Solarflare Server Adapter User Guide
Solarflare Adapters on Linux
Issue 20 © Solarflare Communications 2017 84
Global Flow Count
Configure the number of simultaneous flows that will be managed by RFS. The
suggested flow count will depend on the expected number of active connections at
any given time and may be less than the number of open connections. The value is
rounded up to the nearest power of two.
#
echo 32768 > /proc/sys/net/core/rps_sock_flow_entries
Per Queue Flow Count
For each adapter interface there will exist a ‘queue’ directory containing one ‘rx’ or
‘tx’ subdirectory for each queue associated with the interface. For RFS only the
receive queues are relevant.
#
cd /sys/class/net/eth3/queue
Within each ‘rx’ subdirectory, the
rps_flow_cnt
file holds the number of entries in
the per ‐ queue flow table. If only a single queue is used then
rps_flow_cnt
will be
the same as
rps_sock_flow_entries
. When multiple queues are configured the
count will be equal to
rps_sock_flow_entries
/ N where N is the number of
queues, for example:
rps_sock_flow_entries
= 32768 and there are 16 queues then
rps_flow_cnt
for
each queue will be configured as 2048.
#
echo 2048 > /sys/class/net/eth3/queues/rx ‐ 0/rps_flow_cnt

#
echo 2048 > /sys/class/net/eth3/queues/rx ‐ 1/rps_flow_cnt
Disable RFS
To turn off RFS using the following command:
#
ethtool ‐ K <devname> ntuple off
3.18 Solarflare Accelerated RFS (SARFS)
The Solarflare Accelerated RFS feature directs TCP flows to queues processed on the
same CPU core as the user process which is consuming the flow. By querying the
CPU when a TCP packet is sent, the transmit queue can be selected from the
interrupt associated with the correct CPU core. A hardware filter directs the receive
flow to the same queue.
SARFS is provided for servers that do not support standard Linux ARFS. For details of
Linux ARFS, refer to the previous section. Additional information can be found at the
following link:
https://access.redhat.com/documentation/en ‐ US/Red_Hat_Enterprise_Linux/6/
html/Performance_Tuning_Guide/network ‐ acc ‐ rfs.html
Overall SARFS can improve bandwidth, especially for smaller packets and because
core assignment is not subject to the semi ‐ random selection of transmit and receive
queues, both bandwidth and latency become more consistent.