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The back-end network between compute nodes and PowerScale should be 40 Gbps with Jumbo Frames set (MTU=9162) for the NICs and the switch ports.
Add the following parameters in /etc/sysctl.conf.
Disable TCP timestamps to improve CPU utilization (this is an optional parameter and will depend on your NIC vendor).
net.ipv4.tcp_timestamps=0
Enable TCP sacks to improve throughput.
net.ipv4.tcp_sack=1
Increase the maximum length of processor input queues.
net.core.netdev_max_backlog=250000
Increase the TCP max and default buffer sizes using setsockopt().
net.core.rmem_max=4194304
net.core.wmem_max=4194304
net.core.rmem_default=4194304
net.core_wmem_default=4194304
net.core.optmem_max=4194304
Increase memory thresholds to prevent packet dropping.
net.ipv4.tcp_rmem=4096 87380 4194304
net.ipv4.tcp_wmem=4096 65536 4194304
Set the socket buffer to be divided evenly between TCP window size and application buffer.
net.ipv4.tcp_adv_win_scale=1
Verify which features are available with your NIC using ethtool.
$ sudo ethtool -k <ethX>
There are various offload capabilities that modern NICs (and especially high-performance NICs) have, and it is always recommended to enable them.
A few features such as tcp-segmentation-offload (TSO), scatter-gather (SG), and generic-segmentation-offload (GSO) are good features to enable (if not enabled by default).
Check existing ring buffer sizes.
$ ethtool -g <ethX>
After checking the preset maximum values and the current hardware settings, the following command can be used to resize the ring buffers:
# ethtool –G <interface> rx <newsize>
Or
# ethtool –G <interface> tx <newsize>
Note: The ring buffer sizes depend on the network topology to a certain degree and might need to be tuned depending on the nature of the workload. For 10 G NICs, setting the RX and TX buffers to maximum is reasonable. This setting should be tuned based on the network architecture and type of traffic.