Want to use AIX live update but can't because you're running low on free/spare CPU capacity on your Power Systems frame?

 

Well, with the latest TL for AIX 7.2, you now have a couple of options to help mitigate this problem. On a busy frame, it might be difficult to keep enough free CPUs to allow the creation of the surrogate partition or to run several Live Updates concurrently. Now you can try one of the following solutions:

 

• Live Update Across frames with PowerVC
• Live Update CPU Reduction with PowerVC
• Live Update CPU Reduction with HMC

 

I was particularly interested in the "Live Update CPU Reduction" approach. I performed a couple of tests and found that, in order to use this particular feature, I needed to add the "cpu_reduction = yes" stanza to the /var/adm/ras/liveupdate/lvupdate.data config file. The documentation states that this new option will do the following:

 

#      cpu_reduction = <yes | no> Blank or omitted defaults to no. If yes, the

#         live update operation will, in the absence of sufficient processing

#         capacity to create and boot the surrogate normally, determine whether

#         removing some capacity from the original would result in sufficient

#         available capacity, and if so, will automatically remove

#         the capacity from the original (later to restore the surrogate to full

#         capacity once the original is deleted).

 

 

root@lkutest / # oslevel -s

7200-03-01-1838

 

root@lkutest /var/adm/ras/liveupdate # cat lvupdate.data

general:

        cpu_reduction = yes

       

WARNING! The "white space" in front of the "cpu_reduction = yes" line MUST exist (see below). I added a tab. Without this, the option is NOT recognised by the live update (geninstall) command. This is not documented anywhere and I'm hoping it will not be a requirement in a future AIX update.

 

You can verify the option has been recognised by performing a preview and then checking the liveupdate.cf afterwards. It should show CPU_Reduc set to yes.

 

root@lkutest /var/adm/ras/liveupdate # grep -p CPU liveupdate.cf

CPU_Reduc:

        do = "yes"

...

 

You can find more information on the "cpu_reduction" option here: https://www.ibm.com/support/knowledgecenter/ssw_aix_72/com.ibm.aix.install/lvupdate_configuration.htm

 

With the CPU reduction option, during a live update operation (geninstall -k), the surrogate VMs entitled capacity is "shrunk" to the minimum allowed in the partition profile. After the operation is completed the VM is "resized" to match the original capacity entitlements. This all happens automatically. The following screens shots, from PowerVC, show the VMs "Processing units" before, during and after the live update. They also show the resource alocation and resize operations from the PowerVM Messages view. You can see that the assigned "Processing units" were reduced to 0.1 (based on the VMs partition profile minimum CPU setting; check with 'lparstat -i | grep Mini | grep Cap' on the AIX VM).

 

 

If you don’t use this option and your frame doesn’t have enough CPU capacity to house the surrogate partition, the live update preview will fail, with the following message.

 

1430-200 FAILED: Not enough processing units available on target host.

 

Here's a brief overview of these new options with Live Update.

 

Live update with CPU (processor) reduction:

• Live Update will create the surrogate partition with minimal CPU as in the original partition.
• Live Update reduces the CPU of the original partition up to a minimal amount, so that the surrogate partition could be activated.
• Live Update will use the available CPU and only reduce what is necessary.
• Post Live Update the CPU will be restored to the earlier amount before the reduction.

 

Live Update Across Frames:

• Decision to perform Live Update on the local Host (frame) or migrate to another Host is made depending on the availability of resource in the local Host, the destination Host and user inputs.
• A VM managed by the PowerVC will be migrated to another Host connected through HMC or Novalink and live update operation will be triggered subsequently on the destination Host.
• Post the Live Update operation, the VM will be migrated back to original Host.
• Note: Live Update Across Frames is not currently supported with a HMC.

Tags:  update reduction cpu gibson with aix blog live chris cpu_reduction geninstall