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High System CPU Usage on HP-UX 11i

Sharad Kowarkar_1
Occasional Contributor

High System CPU Usage on HP-UX 11i


We have following set-up
HP-UX 11i 64 Bit
Oracle database
Oracle application 11.5.9

we observed that out usr+cpu usage is quite high almost 100%. sys cpu ranges from 20-70% at times and on average 50%.
Does anybody know why system cpu is very high. I am skeptical about slow I/O since we are using eva5000 2c6d for storage.

Steven E. Protter
Exalted Contributor

Re: High System CPU Usage on HP-UX 11i

1) Make sure the OS and oracle apps are fully patched.

2) Collect some data with the script I'm attaching. It might not be oracle(yeah right).

Steven E Protter
Owner of ISN Corporation
Valued Contributor

Re: High System CPU Usage on HP-UX 11i

Use top or glance to see which process is consuming more CPU, recycle the application or Unix process. You may need patch but you need to identify the process first.
do ? to see different options and q to quit.
By providing solutions I am helping myself
Sharad Kowarkar_1
Occasional Contributor

Re: High System CPU Usage on HP-UX 11i

Hi Guys,
Top doen't show break down of CPU by individual process as [User+Sys]. Is it common behaviour for System CPU to be as high this. I had not seen this behaviour in HP-UX 11.00 with Oracle database and Oracle Application 11.5.4. Can we establish that this kind of "SYS cpu" Usage is abnormal?

Bill Hassell
Honored Contributor

Re: High System CPU Usage on HP-UX 11i

It is not typical for the system usage to be more than 10-20%. Having said that, certain programs can very easily create 50-90% system usage. The question is: is that expected? Slow I/O will not create high system usage. The 'system' metric is for kernel computation, and does not include time when the kernel is just waiting for I/O to comlete. Generally, high system usage is caused by applications that perform massive numbers of system calls--which may or may not be the way the program is supposed to work.

Just to muddy things up a bit, if the applications are always accessing the same area of disk, the EVA storage array may always have the data in buffer RAM and therefore disk response would appear to be in the sub-millisecond range. That would mean that thosands of I/Os could be performed per second, which implies that the driver is very busy and therefore the kernel would show high system usage. You need to check on the I/O count to see if that's the case.

Bill Hassell, sysadmin
Tim D Fulford
Honored Contributor

Re: High System CPU Usage on HP-UX 11i

Good advice from Bill... what do you expect from cloth heads !!! ;-o..

From experience..
o We saw high sys CPU when we were using kernel asynchronous IO on a V-class (lots of CPU) HP-UX 11.0 though
o High sys cpu activity is usually associated with high IO activity. This may not necessarily mean the disks (or network etc) are slow, but merely that they are being used badly. e.g. unnecessary sequential scans, continously reading static information into & out of memory, etc.


Abdul Rahiman
Esteemed Contributor

Re: High System CPU Usage on HP-UX 11i

I think Bill's analysis is great about the high system calls and the impact of high context swtitching could have on the kernel mode cpu usage.

Some thing to add on, you should also look at the memory usage and swapping on the system. If the real memory is too low and system started to paging out to the disks, that could also slwo down things and eat up a good amount of cpu cycles..
vmstat should be your buddy here.

No unix, no fun