User Guide

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• IBM Power systems support various network adapters of different speed and number of ports.
• If you are using the same network adapters as your previous system, initially, the same tuning should be used on the new system.
• Most Ethernet adapters support multiple receive and transmit queues whose buffer size can be varied to increase max packet count.
• The default queue settings are different with different adapters and may not be optimal to achieve maximum message rates in a client-server model.
• Using additional queues will increase CPU usage of the system; so optimal queue setting for a specific workload should be used.
Changing queue size in AIX
• ifconfig enX detach down
• chdev -l entX -a rx_max_pkts =<value> -a tx_max_pkts =<value>
• chdev -l enX -a state=up
Changing queue settings in AIX
To change the number of receive/transmit queues in AIX
• ifconfig enX detach down
• chdev -l entX -a queues_rx=<value> -a queues_tx=<value>
• chdev -l enX -a state=up
Changing queue settings in Linux
To change the number of queues in Linux
• ethtool -L ethX combined <value>
Changing queue size in Linux
• ethtool -G ethX rx <value> tx <value>
Higher speed adapter considerations
• Higher speed networks with 25 GigE and 100 GigE network adapters require multiple parallel threads and tuning of driver attributes.
• If it is a Gen4 adapter, make sure the adapted is seated on a Gen4 slot.
• Additional functions such as compression, encryption and duplication can add latency
Virtualization
• Virtualized networking is supported in the form of SRIOV, vNIC, vETH. Virtualization does add latency and can reduce throughput compared to native I/O.
• Besides the backend hardware, ensure VIOS memory and CPU amounts are enough to provide the required throughput and response times
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IBM PowerVM Best Practices can be very helpful in VIOS sizing
Power10 Quick Start Guide – Network IO Considerations