The algorithms for distribution of logical processors among high/medium/low
polarity have been documented in several recent IBM presentations. See
SHARE proceedings and CMG proceedings for a description. The distribution
is based on the LPAR's share of physical engine capacity. In summary:
- Always have at least one medium polarity
- If physical share is GT 1.5, assign high polarity processors subject to
above rule (e.g., physical share GT 1.5, assign 1 high polarity; if share
GT 2.5, assign 2 high polarity, etc.).
- If remaining share after assigning high polarity is LE 1.5 and remaining
share is GT 1, assign 2 mediums (if at least two logical processors have
been assigned to LPAR).
- If at least two logical processors are assigned, always have at least 2
unparked logical processors
- Park all logical processors not explicitly assigned high polarity or
medium polarity.
The algorithms change somewhat, depending on which APARs have been applied
(for example, the "always have two logical processors unparked" rule is
applicable with APAR OW24272).
The above algorithms are static (that is, the high and medium polarity
processor are formed based on weight/share and do not change unless the
weight/share change). Consequently, the result of the algorithms can be
computed easily using a spreadsheet. IRD LPAR Weight Management algorithms
can change the weight/share associated with an LPAR, so the distribution of
high/medium polarity can dynamically change based on IRD actions.
- If low polarity processors are parked, they can be unparked based on the
utilization of existing unparked logical processors, the demand for more
CPU capacity in the LPAR, the unused capacity share available from other
LPARs, etc. Unparked low polarity logical processors will be parked if the
computer capacity conditions are no longer applicable. Unparked low
polarity logical processors will share equally with the medium processor(s)
in the medium share.
The algorithms that decide to park/unpark low polarity logical processors
are executed every 2 seconds. These algorithms are being revised because
the current algorithms are not sufficiently responsive. For example, the
current algorithms require that all unparked logical processors must be at
least 94% busy before another low polarity logical processor will be
unparked. According to Bernie Pierce (WLM Developer) at his CMG
presentation last month, the revised algorithms should be available by end
of January.
As mentioned, you can put the above algorithms into a spreadsheet and
experiment with various combinations of weight/share among the 3 LPARs each
having 3 logical processors as described by the OP. That will answer any
questions about the distribution of logical processors into high/medium/low
polarity depending on LPAR share of physical capacity. You will notice,
for example, that it is not possible to have TWO medium logical processors
each with a share of 99%. A single medium can have 99%, but if the
combined share of two mediums was more than 150%, then the algorithms would
form one high and one medium.
Regards,
Don
******
Don Deese, Computer Management Sciences, Inc.
Voice: (804) 776-7109 Fax: (8043) 776-7139
http://www.cpexpert.org
******
At 06:26 PM 1/16/2009, you wrote:
If you're curious about how things are being distributed, and have RMF,
the RMF post-processor CPU report will show you the processor share from
an LPAR point of view. Note that Al isn't completely correct, in that
sometimes HiperDispatch may decide to give you two medium CPs (CPs that
have a logical processor share between 1 and 99%) instead of 1 high CP (a
CP with a 100% logical processor share).
---
Kevin McKenzie
External Phone: 845-435-8282, Tie-line: 8-295-8282
z/OS BCP SVT, Dept FXKA, Bldg 706/2D38
Al Sherkow <[email protected]>
Sent by: IBM Mainframe Discussion List <[email protected]>
01/16/2009 09:50 AM
Please respond to
IBM Mainframe Discussion List <[email protected]>
To
[email protected]
cc
Subject
Re: z10 and HiperDispatch question.
That is how HyperDispatch should work. Engines will be pseudo dedicated to
an LPAR. 3 LPARs on a W03 (or U03 of the orig question) with 3 logicals
each
would tend to have one engine at 100% and the other two close to zero (if
all have equal demand) and weights of 33%.
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