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Kernel parameters for Smallworld

 
Peternt
Regular Advisor

Kernel parameters for Smallworld

Hi,
I have a Smallworld CST running in HP-UX 11.11 and I want to configure it for optimum performance.
I have two parameters that I want tune: dbc_min_pct and dbc_max_pct.
The server have 12 GB of physical memory and dbc_min_pct = dbc_max_pct = 10

The performance of Smallworld is better with more memory for the buffer cache ?
Please, provide me any clue or information according your experience.
Thanks in advance
Peter
Roger
15 REPLIES
Andrew Rutter
Honored Contributor

Re: Kernel parameters for Smallworld

hi,

it depends upon what the system needs really, number of open files...

see this link if you havent already, it may help you work out what may be best

http://docs.hp.com/en/939/KCParms/KCparam.DBCminPct.html

Andy
Manix
Honored Contributor

Re: Kernel parameters for Smallworld


Use "SAR" to monitor the buffer cache utilization as then tune it accordingly
using kctune -s =value

$ sar -b 1 10

http://h30499.www3.hp.com/t5/System-Administration/Setting-of-dbc-max-pct-and-dbc-min-pct/m-p/4542185#M369519


Thanks

Manix

HP-UX been always lovable - Mani Kalra
Jose Mosquera
Honored Contributor

Re: Kernel parameters for Smallworld

Dynamic Buffer Cache is the area of memory used by programs when writing to disk. Programs write to buffer cache instead of disk to speed things up.
The cache is then written in large chunks to disk during quieter periods. The time for this in very small figures in milliseconds.

The amount used being dynamically allocated dependant upon system requirements.

At times during system usage a high amount of dynamic buffering can be called for by the OS (i.e backup operations).

The state of buffer caching can be monitored by examining the field %rcache displayed from the sar -b command.

%rcache : Give you the read cache percentage.

This is the most important measurement tool for a resize of buffer cache max setting - 100% means that the systen is finding what it wants 100% of the time in dynamic buffer and is not searching slower systems for data (disk drives). A 99% is very good value.

If the dbc_max_pct is changes to a lower value then the %rcache is the value to monitor to ensure that the reduced size is not forcing the systen to "Look elsewhere".

This in itself will not give a performance increase but will release memory to be used by other system rescources, login, logout, cleanup after vdxusers, etc.

Rgds
Rita C Workman
Honored Contributor

Re: Kernel parameters for Smallworld

If you want kernel tuning assistance, than it would be helpful if you would supply:

1. List of your current parm settings
2. Output of swapinfo -tam
3. Output of sar -v 1 10

That will give folks here at least a little bit more info...

Now for a couple of my favorites to tune:

dbc_max% I'd set it at 10-12
dbc_min% I'd set it at 5

I would run sar -v 1 10 and probably change my ninode to something closer to what the output shows you really need.
With 12Gb of memory I would change the vx_ninode from zero to something more like 40,000 to 60,000.

The outputs from above will help us see what else might be tuned or give folks a clue as to what next to ask...

Kindest regards,
Rita
Peternt
Regular Advisor

Re: Kernel parameters for Smallworld

I've attached:

1. List of your current parm settings
2. Output of swapinfo -tam
3. Output of sar -v 1 10
Roger
Rita C Workman
Honored Contributor

Re: Kernel parameters for Smallworld

hmmm...I can't download this.

Can you post some of it..

Rita
Peternt
Regular Advisor

Re: Kernel parameters for Smallworld

I've attach the file kmtune.txt
Roger
Jose Mosquera
Honored Contributor

Re: Kernel parameters for Smallworld

What about of sar -b output?
Peternt
Regular Advisor

Re: Kernel parameters for Smallworld

I've attached sar -b 1 10

Roger
Rita C Workman
Honored Contributor

Re: Kernel parameters for Smallworld

The text file I can see..

How's about swapinfo -tam and sar -v 1 10

Thanks,
Rita
Peternt
Regular Advisor

Re: Kernel parameters for Smallworld

sarv.txt
Roger
Rita C Workman
Honored Contributor

Re: Kernel parameters for Smallworld

First, I know nothing about Smallworld CST, I tune generally for Oracle.

But...
sar -v shows you the ninode setting is way too high. You are using around 2300 but your set for 13592. Reduce this to maybe 4092 tops for now.

Here is what I generally start resetting, but remember do NOT change alot of parms. Change just 1 or 2, then monitor and see if you need to tune more:

dbc_max% .. fine leave it most I'd go is 12
dbc_min% .. reduce it to 5
maxdsiz .. I'd leave that for now
maxssiz .. May be too big, might be able reduce that to 80Mb.
npty/nstrpty/nstrtel .. set this value up to 200 for all (Just cause default is probably too low)
shmmax .. You have it set for 4Gb, I'd bring it up to 10Gb

vx_ninode .. set at default, I'd change that to 40,000 to 60,000 to start

Adjust dbc_max & min..and those 3 tty/pty parms and rebuild kernel & monitor.

If it's running good...then stay there.
If you feel you need to tune again maybe try
changing ninode & vx_ninode...rebuild kernel & monitor.

Again, if things are running good stay there. If not then think about adjusting shmmax...monitor.

You will have to monitor the box and determine which change to make and in which order. Do not take what I said as cast in concreate...you decide what and when to make it....

..I think it was Stephen Cuillo who said that 'tuning is more art than science'.

Regards,
Rita

Re: Kernel parameters for Smallworld

>Rita: I can't download this.

This is a known problem with the forum, .zip and IE.

Rita C Workman
Honored Contributor

Re: Kernel parameters for Smallworld

Thanks Dennis !

That is the disadvantage of not being regular in the Forums...you miss stuff.

Rita

...I am so going to miss this site...
Peternt
Regular Advisor

Re: Kernel parameters for Smallworld

Thanks
Roger