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Old 04-28-2004, 08:14 AM   #1
stephnane
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Registered: Apr 2004
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kernel takes a lot of CPU


Hi.

When I do a "topas" on my AIX server, it shows that my kernel takes 60%, users 40%, wait 0% and Idle 0%.
Is it good/right ?
How can I see what my kernel does ?
ps -ef gives me users informations, but what about the kernel ?

Tks

stephane
PS: excuse me for my english ...
 
Old 04-28-2004, 09:18 AM   #2
iainr
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Most processes have kernel and user components. "Kernel" CPU is when the kernel is doing something (e.g. making system calls, talking to devices, checking permissions), "User" is when the process is doing something on its own without the kernel being involved.

The figures you have look OK. The balance between kernel and user components will depend on the individual applications and what you are doing with them.

However, the rule of thumb is that you add together kernel and user to get the total CPU%. In your case, the total CPU% is 100 which means you are CPU-bound : this might be OK for batch jobs, but will be hurting performance for any interactive work.

Look at the top CPU-hogging processes (ps aux sorts processes by CPU use).
 
Old 04-28-2004, 01:46 PM   #3
zorba4
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Of course, this means that you are using all of your cpu power. 60-40 is a good ratio.
If is the cause from time to time, don't panic.
If this occurs 24 hiours per day, and if you find it not comfortable, you should consider buying extra cpu's if you have a multi-cpu upgradable machine.
Regards
Zorba
 
Old 04-29-2004, 08:41 AM   #4
Mark Taylor
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Registered: Apr 2004
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err... no, this is not good .... looks like your system is cpu bound.

usr + sys constantly above 80% = cpu bound

You need to work out what kernel task is spinning, you could be hitting one of many kernel routine spin defects.

what level of code are you running ? what ML levels ?

run tprof / pprof to work out what is using the most cpu ticks and post the offending routine / proc / system call then i should be able to teel you if its a known defect or not...... could be that you just need more cpu power, but you want to rule out the cheapest options 1st like APARs.

HTH
Mark Taylor
 
  


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