Jumbo frames

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Jumbo frames are Ethernet frames with a payload greater than the standard maximum transmission unit (MTU) of 1500 bytes.

The standard MTU must be set to 1492 bytes when using Point To Point Protocol over Ethernet (PPPoE) connectivity.

To enable jumbo frames for testing with the ECM workload, the MTU was set to 8192 for the complete SUT. This included the workload driver machine running on x86_64.

Jumbo frames can be easily enabled in Linux™ by setting a larger MTU in the network configuration file for a network interface. The network interface needs to be restarted after a MTU change to become effective.

Note: Best network performance can be achieved when the entire network and also the physical network switches support jumbo frames.

The following examples show the jumbo frame MTU for a network interface:

# cat ifcfg-eth1 
…
MTU='8192'
…

# ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 02:8C:44:00:00:06  
          inet addr:10.196.39.122  Bcast:10.255.255.255  Mask:255.0.0.0
          inet6 addr: fe80::28c:4400:100:6/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:8192  Metric:1
          RX packets:701 errors:0 dropped:0 overruns:0 frame:0
          TX packets:925 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:63956 (62.4 Kb)  TX bytes:93435 (91.2 Kb)

For information about additional TCP/IP tunings that might be effective for very highly utilized network interfaces, refer to the article Linux on System z® – Tuning hints and tips at this IBM® developerWorks® URL:

https://www.ibm.com/developerworks/linux/linux390/perf/tuning_networking.html