One of the troubleshooting tools I will be covering in the Summit Session SUM305 is Ethtool.

Here I would like to provide more details on setting of off-load and checksumming parameters. There are some scripts on other blog sites that will automatically disable most of these settings in order to improve performance but I do not recommend this be done in a production environment without understanding why these settings are being modified.

Here are some links to definitions and explanations of what each of these parameters affect.

TSO-TCP Segmentation Offload
GSO- Generic Segmentation Offload
UFO- UDP Fragementation Offload

You can manually set checksumming and off-load parameters using ethtool -K but those changes are not persistent across reboots. Making a change this way allows you to test the results prior to making the change persistent.

For Example:

ethtool -K eth0 tx off

ethtool -K vif5.0 tso off

Note: It’s not recommended to use ethtool to disable TSO for vifs. It is best practice to disable it within the VM OS

To make a setting persist across a reboot use the following syntax:

xe pif-param-set uuid=<UUID of PIF> other-config:ethtool-tx=”off”

xe vif-param-set uuid=<UUID of VIF> other-config:ethtool-tso=”off”

Use the table below for the syntax key for ethtool settings:
(Table taken from XenServer 4.1 online docs)

Key Description Valid Settings
ethtool-rx Specify if RX checksumming is enabled on or true to enable the setting, off or false to disable it
ethtool-tx Specify if TX checksumming is enabled on or true to enable the setting, off or false to disable it
ethtool-sg Specify if scatter-gather is enabled on or true to enable the setting, off or false to disable it
ethtool-tso Specify if tcp segmentation offload is enabled on or true to enable the setting, off or false to disable it
ethtool-ufo Specify if UDP fragmentation offload is enabled on or true to enable the setting, off or false to disable it
ethtool-gso Specify if generic segmentation offload is enabled on or true to enable the setting, off or false to disable it
ethtool-autoneg Specify if autonegotiation is enabled on or true to enable the setting, off or false to disable it
ethtool-speed Set the device speed in Mb/s 10,100,or 1000
ethtool-duplex Set full or half duplex mode half or full

SUM305 – Overview of XenServer distributed virtual switch/controller and troubleshooting network issues

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