VM's are slow after upgrading XEN Host to SLES 11 SP2

This document (7012823) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 11 Service Pack 2
SUSE Linux Enterprise Server 11 Service Pack 3

Situation

After upgrading a XEN Host (Dom0) end user's complain about slow application performance.
IP throughput appears to be considerably slower at times

Resolution

Switch from using kernel threads/processes to 'tasklets' for the netback pv driver.

To switch from threads back to tasklets for the netback pv driver:

add
"options netbk tasklets=1 bind=0"
to the modprobe.conf.local file.
A re-boot of the Host is required to instantiate the change.

Note: The bind option is to specify the processor you want them to run on. Default is 0 if left blank

To verify the change took effect, begin a file download on one of the vm's.
Then issue the following command:
ps aux | grep netback

If threads are still being used you will see the netback process in the output.
root      5219 0.0 0.0      0     0 ?        S    Jan19   0:00 [netback/0]
root      5220 0.0 0.0      0     0 ?        S    Jan19   0:00 [netback/1]

They will be absent if tasklets are in use.

Requires a XEN kernel dated 01/26/2013 or later on SLE11 SP2.

Cause

In SLES 11 SP2 the XEN architecture was re-designed to use server threads to handle the VM IP traffic.
Previously, "tasklets" handled the IO.

Tasklets are the preferred method for VM-to-VM IP traffic.

Additional Information

Disclaimer

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