Troubleshooting for performance issues

Table 1. Performance. Troubleshooting for performance issues
Symptom High volume traffic through an emulated OSA-Express® ethernet adapter on ZVDT suffers poor throughput.
Problem Determination

If newer Linux® kernels are installed, you might experience a drastic slowdown of OSA performance, This slowdown is immediately obvious and is due to Linux attempting to offload various functions into the adapter, which is not acceptable to the current awsOSA implementation. One or more of the following commands, intended to disable the Linux offloading of IP functions, might improve the situation:

# ethtool -K eth0 rx off (disable RX checksumming offload)
# ethtool -K eth0 tso off (disable TCP segmentation offload)
# ethtool -K eth0 gso off (disable generic segmentation 
# ethtool -K etho gro off (disable generic RX offload)
# ethtool -K eth0 lro off (disable large RX offload)
# ethtool -K eth0 rxvlan off (if you are using VLANs)
# ethtool -k eth0 (display status of NIC)
# ethtool -S eth0 (display statistics)
# ethtool -K em1 rx off (newer style of NIC naming)
# ethtool -K enp0s25 rx off (newer style of NIC naming)

You might need to experiment with these commands.

These commands must be entered after each Linux boot. If a script is used to start ZVDT, such as the runzpdt script shipped with the product, that script can be modified to enter one or more of these commands each time ZVDT is started.

Effective combinations of these options differ with various Linux levels and with various NIC adapters. This problem was first noticed with Linux kernel level

If frames larger than expected are used, an excessive number of frames might be dropped (causing a re-transmission). This may not be noticed unless careful measurements or comparisons are made. This problem might be resolved by including the sysctl parameter that is now recommended:

Symptom ZVDT performs slowly. CPUs reach 100% utilization.
Problem Determination Verify that you are meeting the minimum requirements for both the hardware and the software. See Hardware and software requirements.