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  3. March 2006

Re: Giving more than 110%

Dave,
This goes against what I thought I understood. Of course I could easily be wrong so I just want to be clear.
It has always been my understanding that if I had 1 virtual processor and 0.10 processor assigned to a partition I would still see the processor utilization on a 0 to 100% scale even though I techincally can only use 10%. In WRKSYSACT I would see the process QHLPVTASK using 9 times the amount of CPU that the rest of the system was using. So if my actual processor utilization was 0.05 then I would see QHLPVTASK using 45% of a processor so that WRKACTJOB/WRKSYSSTS shows 50%. (After all in this case I'm using 50% of what I've assigned to the partition)
The other rules as you explain them are exactly as I understood so I'd like to know if there is something I am misunderstanding. 

Thanks,

- Larry

Dave Schnee wrote:

Kirk:
What probably happened to you was that you were on a System i5 machine with "uncapped processors" and LOTS of unused CPU power in the processor pool. In that instance, you can "borrow" CPU cycles from other partitions' allocations if you have your "virtual processors" number set higher than the actual processor(s) you are assigned. Since you must have at least 0.10 processor assigned for each virtual processor you assign, the most you can get is 1,000% (even if there are more processors still idle) because i5/OS will only dispatch as many concurrent jobs as there are virtual processors.
In your example, you were assigned 0.50 processing units and could, therefore, assign up to 5 virtual processors (simultaneous threads executing). That would allow you to use 1,000% of the CPU you were assigned. If there were not enough idle CPU cycles in the processor pool, you would have used less than 1,000% despite your assignment of virtual processors.
Had you assigned 1 virtual processor with 0.50 processor units, you could have gotten only to 200% CPU usage if there were otherwise-idle CPU cycles (due to other partitions not using their full allocations).
There is a Red(something) - either a RedPaper of RedBook - I'm not sure which it will become - that is currently being reviewed before publication by IBM. I am one of the authors and there is a rather complete treatise on this topic in that writing. The publication number has been assigned as SG24-7174 and the current working title is "Automating Dynamic LPAR on iSeries and System i5 utilizing APRM". I hope it gets "out" soon - this is not a well-known concept. 

Dave Schnee,
Barsa Consulting Group, LLC

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