LinuxQuestions.org
Latest LQ Deal: Latest LQ Deals
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Software
User Name
Password
Linux - Software This forum is for Software issues.
Having a problem installing a new program? Want to know which application is best for the job? Post your question in this forum.

Notices


Reply
  Search this Thread
Old 09-14-2009, 05:49 AM   #1
iamjayanth
Member
 
Registered: Oct 2008
Posts: 51

Rep: Reputation: 15
What is user mode jiffies and kernel mode jiffies of a process


Hi all,

I am trying to learn /proc/<pid>/stat file contents. And when I come across two labels

user mode jiffies
kernel mode jiffies

I try to google for jiffies, and I got this data.

Quote:
An incrementing counter representing system "uptime" in ticks - or the number of timer interrupts since boot. Ultimately the entire original concept of a jiffy will likely vanish as systems use timer events only when necessary and become "jiffyless".
What this tells me is that jiffies is a global variable that starts from zero and increments in each clock intervals(cycle).I didnt understand the second sentense in that quote.

Also why process have user mode jiffies and kernel mode jiffies. if these times tell how many times this process executed in user space and in kernel space(system calls) respectively ? Please help
 
Old 09-14-2009, 06:26 AM   #2
lutusp
Member
 
Registered: Sep 2009
Distribution: Fedora
Posts: 835

Rep: Reputation: 102Reputation: 102
Quote:
Originally Posted by iamjayanth View Post
Hi all,

I am trying to learn /proc/<pid>/stat file contents. And when I come across two labels

user mode jiffies
kernel mode jiffies

I try to google for jiffies, and I got this data.



What this tells me is that jiffies is a global variable that starts from zero and increments in each clock intervals(cycle).I didnt understand the second sentense in that quote.

Also why process have user mode jiffies and kernel mode jiffies. if these times tell how many times this process executed in user space and in kernel space(system calls) respectively ? Please help
The reason jiffies will go away is because the original way the kernel used to slice up time for processes is changing. Processes will no longer get a time slice unless they actually need it, which renders the jiffie scheme meaningless.

"Multitasking" once meant an arbitrary division of processor time between all running processes. Now the kernel scheduler can avoid assigning time to a process that doesn't actually need the time.

Jiffies are separated into kernel and user space because system administrators want to know how much time is spent in kernel routines versus user-space code.
 
Old 09-15-2009, 12:35 AM   #3
iamjayanth
Member
 
Registered: Oct 2008
Posts: 51

Original Poster
Rep: Reputation: 15
Thanks lutusp for the reply...

So you are saying that at present scheduler allocates a time slice for each and every process beforehand, without checking whether they need that or not...And scheduler allocates this time in units of jiffies...
And in future(?) each and every process need to request for there exicution time, which a scheduler can provide.

Then pre calculation of time for processes in terms of jiffies will go making jiffies meaningleass....


Am I understood correctly...

Sorry if my english is wrong...
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



Similar Threads
Thread Thread Starter Forum Replies Last Post
How to check the affection of jiffies overflow in kernel 2.4.18. shiner_chen Linux - Kernel 2 07-22-2008 09:37 PM
Jiffies a kernel only entity, or is it allowed in userspace also? pat_and_cami Programming 0 03-10-2006 01:36 AM
Kernel compiling problem, connected with jiffies.h zWaR Linux - Software 2 03-01-2006 06:30 PM
Interface between user mode and kernel mode santosh_pn Linux - Software 1 06-17-2005 08:20 AM
start date and start time of a process - jiffies Yoko Programming 0 12-04-2004 09:12 AM

LinuxQuestions.org > Forums > Linux Forums > Linux - Software

All times are GMT -5. The time now is 03:30 AM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration