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Logical Processors - LPARs Max limit

 
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vasanthz

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PostPosted: Sat Oct 26, 2013 12:49 am    Post subject: Logical Processors - LPARs Max limit
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Hi,

I have a doubt with the number Logical processors assigned to an LPAR.

Suppose if we have a box with 500 MSU and there are 3 lpars on the box.


LPAR 1 is assigned 3 logical processors &
LPAR 2,3 are assigned 1 logical processor each. (3+1+1=5)


Does this mean that LPAR 1 can run a maximum of 300MSU?
LPAR 2 and 3 run at maximum of 100 MSU's each?


Please let me know how logical processors concept works or point me to some documentation where I could get information.

12:49AM Friday and still duet with mainframes continues :S
Thanks & Regards,
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Robert Sample

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PostPosted: Sat Oct 26, 2013 1:12 am    Post subject:
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How many processors in the box? And, more critically, what are the weights assigned to each LPAR?
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Robert Sample

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PostPosted: Sat Oct 26, 2013 1:25 am    Post subject:
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Sorry, I forgot to include a link. The manual is Planning Workload Management in the MVS bookshelf, and the link for 1.12 of z/OS is http://pic.dhe.ibm.com/infocenter/zos/v1r12/index.jsp?topic=%2Fcom.ibm.zos.r12.ieaw100%2Fiea2w1b076.htm
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vasanthz

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PostPosted: Mon Oct 28, 2013 10:39 pm    Post subject:
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Hi Robert,

Thank you for the link.. it explains clearly the concept of weights for LPARS.

So weights for lpars are like service classes for jobs right? weights are used to assign CPU resource between LPARS during 100% utlization.


Quote:
How many processors in the box? And, more critically, what are the weights assigned to each LPAR?


Assuming 5 CPs with 500 MSU, if its not too absurd & uncapped.
LPAR1 - 3 logical processors - 200 weight
LPAR2 - 1 logical processor - 200 weight
LPAR3 - 1 logical processor - 100 weight.

So if weights decide the resource allocation to LPAR during max utilization, does logical processor count for LPAR also play any part in it?

Warm regards,
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vasanthz

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PostPosted: Mon Oct 28, 2013 11:06 pm    Post subject:
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Robert,
http://gibsonnet.net/aix/ibm/Converting_LPAR_Weights_to_Logical_Processor_Allocation.pdf

Found this pdf about how lpar weights & logical processors work together.
I guess there are some inaccuracies in the the number of logical processors mentioned on the link, but it gives a pretty good idea.

Thanks & Regards,
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Robert Sample

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PostPosted: Tue Oct 29, 2013 12:04 am    Post subject:
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Vasanth:

I'm glad you found that link. The last two paragraphs are particularly worth noting:
Quote:
This calculation is always applicable - even when the LPAR runs at less than 100% capacity. If an LPAR does not
use its allocation, the extra CPU cycles are re-allocated based on existing weights defined to other uncapped LPARs
requesting more CPU. However, capped LPARs cannot acquire more CPU cycles than their assigned weight, even if
those cycles are available.
With dynamic timeslicing, the LPAR weight is a guaranteed minimum, not a maximum allocation CPU resource. If all
LPARs use their allotted share, this would be the amount of processing that could be performed. If the A1-A11
LPARs had little activity, the A12 LPAR could get as much as 90% of each logical engine in its assigned time.
A few points to be VERY clear on:
1. WLM does its best when the LPAR is running at 100% utilization, but it will do what it can when the LPAR is less used.
2. Capping an LPAR impacts the overall results.
3. Dynamic timeslicing also impacts the overall results (especially when some of the LPARs are under-utilized).
4. Giving an LPAR 10% of the system does NOT mean the LPAR is going to always get 10%; sometimes it will get less and sometimes it can get more (unless capped).
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vasanthz

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PostPosted: Tue Oct 29, 2013 1:43 pm    Post subject:
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Thanks Robert, Im slowly absorbing the concept.
I owe u a drink, more like a case of drinks :-)

Regards,
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