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Kernel Parameters: semmni, semmns, semmnu & semume

 
sysad1_1
Advisor

Kernel Parameters: semmni, semmns, semmnu & semume

Hi Gurus,

Can you help me determine what these kernel parameters are for?

I have read what semaphores are but still I can't understand what values should I use for these four parameters.

My interest to semaphores started out when we connected a new storage to our HP PA-RISC Superdome server wherein our storage vendor recommended the following kernel parameter values:

semmni=256
semmns=256
semmnu=256
semume=256


Right now, here's what I have presently at my operating system set:
semmni 9410 - 9410
semmns 18780 - 18780
semmnu 4830 - 4830
semume 64 - 64

I don't know if this is the default when you install HP-UX or of this has already been tweaked. Regardless of this, (1) I still want to understand in detail what semaphores are, (2) Its relation to storage (3) How will a certain value for these kernel parameters have an effect to my performance?

I am not familiar with HP-UX performance tuning I badly need your help on this.



TIA
5 REPLIES
sysad1_1
Advisor

Re: Kernel Parameters: semmni, semmns, semmnu & semume

let me also add as number 4:

(4) how are these semaphore kernel parameters related to the number of volume groups?
ani007
Super Advisor

Re: Kernel Parameters: semmni, semmns, semmnu & semume


it is kind of flag (in abstract terms) which every process will check before processing ahead to avoid the deadlock situation.
A semaphore is a term used in UNIX for a variable which acts as a counter.Ex.suppose two processes try to access the same file simultaneously.The value of the semaphore is initialized by the first process when the file is in access by it. When the second process try to access the file it checks the value of the semaphore and if it finds the value as initialized it does not access the file. After the first process is completed it reinitializes the semaphore value and now the second process uses it. The above example is for two processes but a semaphore can be used even when numbers of processes try to access the same file. Thus semaphores are used to coordinate access to a resource by different processes.

As A semaphore is a flag of a process state and can be related to memory
Universe uses semaphore for :-

? File lock semaphores
? Group/update record lock semaphores
? Login semaphore
? Port status semaphore
? Dynamic file semaphore
? Transaction logging semaphore


http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=3480

Regards,
Ani
sysad1_1
Advisor

Re: Kernel Parameters: semmni, semmns, semmnu & semume

My next question is what the appropriate number of semaphores for a specific number of VGs?
Tim Nelson
Honored Contributor

Re: Kernel Parameters: semmni, semmns, semmnu & semume

what are you really trying to accomplish ?

the number of volume groups is typically controlled by the kernel parameter maxvgs.

the sem* settings are typically for application use to use as messaging flags between processes.

James R. Ferguson
Acclaimed Contributor

Re: Kernel Parameters: semmni, semmns, semmnu & semume

Hi:

Section-5 of the HP-UX manpages offers a good overview of these parameters. For 11.31 (for example) see:

http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c02456334/c02456334.pdf

Regards!

...JRF...