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Full Discussion: Newbie & LPAR
Operating Systems AIX Newbie & LPAR Post 302493607 by zaxxon on Thursday 3rd of February 2011 10:38:22 AM
Old 02-03-2011
I had a similar question about the monitoring of CPU usage on logical CPUs. I was trying to sort out some nmon reports and came to no conclusion. So I asked Nigel Griffiths (coder of nmon) in the IBM developerWorks forum about it:

https://www.ibm.com/developerworks/f...557461�
Quote:
...
I agree the logical CPU stats are largely meaningless for shared CPU partitions because the logical CPUs don't really exist as we think of them (they are sharing in unpredictable ways the underlying physical CPUs and certainly don't have fixed percentages of CPU time like 50:50) and especially when uncapped as its reported as 100% busy when its really say 5 times the entitlement which you could call 500% !!

Pay attention to the Physical CPU use (also called CPU used).
...
---------- Post updated at 04:38 PM ---------- Previous update was at 02:17 PM ----------

In addition to my previous somewhat general post:

Your assumption sounds correct to me, if the process is single threaded. If it is multithreaded and SMT is enabled, it should be dispatched by different logical CPUs and so take advantage being able to run multiple threads on multiple logical CPUs.
You can check dispatching with mpstat -s 1 for example.
There is also a "Virtualization best practices" Redbook - maybe this has information about it.

A single threaded process will most probably not take any advantage of SMT or having more than 1 virtual CPU available, if it is running mainly alone on the system. It can only be handled by one virtual CPU at a time. Though a second virtual CPU can meanwhile handle other operating system tasks etc. In that case turn of SMT and monitor it's performance.

For tests you could try out nstress.

You might want to check out what is best for your environment/application.
To check out if your application is multithreaded, check it out with svmon -P| grep -p Pid. There will be a Y in the column for Mthrd.

In our environments we have SMT turned on, because on every LPAR there is usually running single and multithreaded processes and we had no need to turn SMT yet off.

Last edited by zaxxon; 02-03-2011 at 11:42 AM.. Reason: changed "virtual" to "logical"
 

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DISKTAB(5)						      BSD File Formats Manual							DISKTAB(5)

NAME
disktab -- disk description file SYNOPSIS
#include <disktab.h> DESCRIPTION
disktab is a simple database which describes disk geometries and disk partition characteristics. It is used to initialize the disk label on the disk. The format is patterned after the termcap(5) terminal data base. Entries in disktab consist of a number of `:' separated fields. The first entry for each disk gives the names which are known for the disk, separated by `|' characters. The last name given should be a long name fully identifying the disk. The following list indicates the normal values stored for each disk entry. Name Type Description ty str Type of disk (e.g. removable, winchester) dt str Type of controller (e.g. SMD, ESDI, floppy) ns num Number of sectors per track nt num Number of tracks per cylinder nc num Total number of cylinders on the disk sc num Number of sectors per cylinder, ns*nt default su num Number of sectors per unit, sc*nc default se num Sector size in bytes, DEV_BSIZE default sf bool Controller supports bad144-style bad sector forwarding rm num Rotation speed, rpm, 3600 default sk num Sector skew per track, default 0 cs num Sector skew per cylinder, default 0 hs num Headswitch time, usec, default 0 ts num One-cylinder seek time, usec, default 0 il num Sector interleave (n:1), 1 default d[0-4] num Drive-type-dependent parameters bs num Boot block size, default BBSIZE sb num Superblock size, default SBSIZE ba num Block size for partition `a' (bytes) bd num Block size for partition `d' (bytes) be num Block size for partition `e' (bytes) bf num Block size for partition `f' (bytes) bg num Block size for partition `g' (bytes) bh num Block size for partition `h' (bytes) fa num Fragment size for partition `a' (bytes) fd num Fragment size for partition `d' (bytes) fe num Fragment size for partition `e' (bytes) ff num Fragment size for partition `f' (bytes) fg num Fragment size for partition `g' (bytes) fh num Fragment size for partition `h' (bytes) oa num Offset of partition `a' in sectors ob num Offset of partition `b' in sectors oc num Offset of partition `c' in sectors od num Offset of partition `d' in sectors oe num Offset of partition `e' in sectors of num Offset of partition `f' in sectors og num Offset of partition `g' in sectors oh num Offset of partition `h' in sectors pa num Size of partition `a' in sectors pb num Size of partition `b' in sectors pc num Size of partition `c' in sectors pd num Size of partition `d' in sectors pe num Size of partition `e' in sectors pf num Size of partition `f' in sectors pg num Size of partition `g' in sectors ph num Size of partition `h' in sectors ta str Partition type of partition `a' (4.2BSD filesystem, swap, etc) tb str Partition type of partition `b' tc str Partition type of partition `c' td str Partition type of partition `d' te str Partition type of partition `e' tf str Partition type of partition `f' tg str Partition type of partition `g' th str Partition type of partition `h' FILES
/etc/disktab SEE ALSO
getdiskbyname(3), disklabel(5), disklabel(8), newfs(8) HISTORY
The disktab description file appeared in 4.2BSD. BSD
June 5, 1993 BSD
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