IO wait more in sar output

vinodan — Thu, 19 Apr 2007 11:55:32 GMT

Dear All,

When i ran "sar -u" in our HPUX 11.23 system i found % system CPU is more than % User CPU . As per my knowledge best ratio is 70% (user mode) and 30% (system mode).Kindly go through the attachment for further details ...

These are my doubts

1) What can be the various reasons which can cause increased % system mode operation of CPU than User mode ?
2) Normally if application code is using more system calls this issue may come . But the samecode is running in similary configuredmachine (with same hardware / O.S
configuration ) with out this problem .

Various outputs are attached .Can anyone suggest what casues this problem ?

Vinod

Re: IO wait more in sar output

Steven E. Protter — Thu, 19 Apr 2007 12:04:48 GMT

Shalom,

The ratio of user to system totally depends on how the system is being used and what applications you are running. Your attachment indicates this is an Oracle server.

1.) The assumption you make is false, there is no ideal ratio of system to user. A system that has a high user ratio can be one with an extremely efficient OS set up and good applications running on it. Note further I see significant idle time on your system which means its not being pushed very hard.

2.) I challenge as to whether there is a problem based on the available data.

The original "complaint" is that certain ratios on a sar report are not ideal. I normally don't bother looking for problems unless a report indicates an issue, such as excessive I/O or more likely users complain of poor response time.

Memory use is low, swap is being reserved but proceses not swapped out.

I don't see a problem here. Maybe take a larger performance data sample. Here is a link to some nice sar scripts.

http://www.hpux.ws/system.perf.sh

This site will be down from 2-4 p.m. for critical network maintenance, Central time, only the day of this post.

SEP

topic IO wait more in sar output in Operating System - Linux

IO wait more in sar output

Re: IO wait more in sar output