nmon question

[alexia32]

Hello

I have the nmon tool running and generated the graphs (website or using nmon analyser).
The aix server is 5.3TL8 and have 5 physical CPU allocated, 10 Virtual cpu and smt enable so 20logical cpu seen by nmon.

On the graph I can see that 15CPU are used almost 99% but the 5 other cpu are 100% idle...

and the graph cpu_all give of course a wrong info saying 60% of cpu is only used (because I suppose of the 5 cpu unsed)

Comparing with lpar2rrd, from the hmc, I can see that the whole 5 cpu are 100% used almost all the day.

Any idea why the system seeing 20cpu (10virtual cpu with smt enable) used only 15 cpu at 100% all the time and leave the other 5 unused?

thanks in advance
Cheers
al

 

[khalidaaa]

I think this depends on the load you are running on your box! If the processes running use intensive multithreading then you might be using the whole 20 logical CPU but it seems that for your load only 15CPU are enough.

(hint, smt stands for simultaneous multithreading)

Regards,
Khalid

 

[alexia32]

Hi

Thanks for the reply. So in your opinion if the application doesn't require more cpu it will use the 15 cpu at almost 99% all the time and leave the other 5 unsued but this has an impact on the performance.
I wonder how we can force to use all the cpu...
Thanks again
Al

 

[khalidaaa]

This shouldn't be a performance problem if you are using the multithreading feature (which i'm sure you do)

Have you been monitoring the run Q? what's the maximum number of processes in the run Q?

Regards,
Khalid

 

[khalidaaa]

These links could be relevant:

http://www.ibm.com/developerworks/aix/library/au-aix5_cpu/index.html

http://www.ibm.com/developerworks/forums/thread.jspa?threadID=98179&tstart=30

http://www.ibm.com/developerworks/aix/library/au-aixoptimization3/index.html

Regards,
Khalid