Vmstat interpretation

[Becke]

Hi Guys,

I'm trying to interpret vmstat output on an AIX machine, I need to know what 'cs' field is really and how it works, what are the numbers underneath the 'cd' field..

Well 'cs' means context switch, but what is a context switch???

2. My other question is underneath the 'fre' field if this field is closer to zero constantly, does that mean we need to add more physical memory????

Thanks Guys
Raf

[A. Clay Stephenson · Accepted solution]

Context switch = process switch

Process A is run a little while; then Process B is run a little while; then Process C; then Process A ... each of these is a context switch

[Becke]

Thanks Stephenson for your help and quick response. I have a couple of more queries.
Question 1. If the process is being blocked in the CPU waiting for something, what could the CPU be waiting for? If the CPU is waiting for something then is it still CPU bound??

Question 2. underneath the 'fre' field if this field is closer to zero constantly, does that mean we need to add more physical memory????

Thanks for your help, we have a great team here.

Kind Regards,
Raf

[Kent Ostby]

Raf -- Take a look at this page regarding AIX and the memory management system:

http://www.unixguide.net/ibm/faq/faq1.300.shtml

Best regards,

Oz

[Becke]

Thanks for your quick response, I'm doing lot of research and reading documents...

Thanks Guys

[Arunvijai_4]

Hi Raf,

Some good links about Unix Processes,

http://heather.cs.ucdavis.edu/~matloff/UnixAndC/Unix/Processes.html
http://userpages.umbc.edu/~jack/ifsm498/processes.html

-Arun

[Becke]

Thanks Arun

[Chauhan Amit]

Hi Raf,

Replies are Inline to your questions:

Question 1. If the process is being blocked in the CPU waiting for something, what could the CPU be waiting for? If the CPU is waiting for something then is it still CPU bound??

No . For ex. CPU may be waiting for I/O , In this case it will be I/O Bound.

Question 2. underneath the 'fre' field if this field is closer to zero constantly, does that mean we need to add more physical memory????

Yes . Suggest to Compare this value with other systems having plenty of Memory.

[Muthukumar_5]

1) Regarding cs:

cs = context switching.

Switching process in processor resource usage based on priroity. It uses a scheduling method for switching.

2) free field on memory?

Is it free field on memory right. Not fr field on page.

If so,

It is indicating free virtual memory available presently. You can also interpret with sam as,

sam -> performance monitor -> system properties -> memory tab for all activities

--
Muthu

[Muthukumar_5]

To get process based memory and cpu statistics then,


# UNIX95= ps -ef -o sz,vsz,cpu,pcpu,pid,comm

it will give that.

--
Muthu

[Arunvijai_4]

Hello Raf,

You can use #swapinfo -tam.

-Arun

[Darrel Louis]

Hi,

If you've Glance on the servers, you use it to analyse why CPU, Disk or Memory usage for a specific process is high.
What is blocking etc.

Darrel

[Becke]

Muthu one more question,

So a context switch is physical thing on CPU or doest context swictch means proceses in processor resource as you said??? and I'm not able to read a lot about it on internet, if you could sched more light on context switch in a bit more detail...and in the vmstat ouput under 'cs' field what those numbers means when they changes, and whether the system is cpu bound or ioound??

Thanks Muthu and everyone for your responses, your info would definitely help, I have also done lot of reading on vmstat, so i can understand better how each field works....



Thanks Guys, I will assign points now...

[Arunvijai_4]

Hi Raf,

You asked,
So a context switch is physical thing on CPU or doest context swictch means proceses in processor resource as you said??? and I'm not able to read a lot about it on internet, if you could sched more light on context switch in a bit more detail...and in the vmstat ouput under 'cs' field what those numbers means when they changes, and whether the system is cpu bound or ioound??

Yes, It is physical thing related to Processor. Just remember, Unix is a time sharing, multi tasking OS, where all the processes share the same resource like CPU, RAM, etc..

Hope this is clear.

-Arun

[Becke]

Thanks for your response Arun, do u have any idea when interpretting vmstat ouput, what does this field 'cs'(ie context switch) means, how do u determine whether the system is cpu bound or i/o bound, by looking at the numbers underneath this particular'cs' field.

Thanks for your response

[Arunvijai_4]

Hi Raf,

A bound CPU is a CPU that is assigned to and handles I/O interrupts for a virtual partition. Every virtual partition must have at least one bound CPU to handle its I/O interrupts.

CPUs that are not assigned to any virtual partition or that are assigned to a virtual partition but do not handle its I/O interrupts are unbound CPUs. Unbound CPUs are sometimes called floater CPUs.

-Arun

[Arunvijai_4]

Hi Raf,

Here is a good Wikipedia link,
http://en.wikipedia.org/wiki/Context_switching

It will clear all the doubts you have.

-Arun

[Becke]

I appreciate your help mate, I'm already doing lot of research on the net and I will look at this site too...

Thanks
Raf

[Arunvijai_4]

Hi Raf,

You can assign points as well, :-)

-Arun

[Becke]

Thanks Arun, I always assign points and in this instance, I have assigned points as well, thanks for reminding me....

[Steven E. Protter]

You have covered some really advanced topics here.

The book linked below covers this stuff in an understandable way and in more detail. I recommend it.

http://www.amazon.com/gp/product/0131463969/ref=sr_11_1/002-9020949-4683225?%5Fencoding=UTF8

SEP

[Becke]

Thanks Steven, we have a great team here.

Regards,
Raf