a question about Process Priority.

corone · 10-07-2010, 01:00 AM

Code:

# ps
22355 pts/3    00:00:00 bash
#
# ps -l 22355
F S   UID   PID  PPID  C PRI  NI ADDR    SZ WCHAN  TTY        TIME CMD
0 S   519 22355 22354  0  75   0    -  1338 wait4  pts/3      0:00 -bash
#
# ps -o pid,priority,command 22355
PID   PRI  COMMAND
22355  15    -bash
#

Why are the priority values of the process different?
What is the difference?

Is the value 15 the "nice" priority?
Then, what is the value 75?

Please, explain the difference of each result.
Thank you.

neonsignal · 10-07-2010, 05:04 AM

The short answer is that there is a history of different *nix systems (and even different Linux kernels) having different priority systems.

The nice level is just a relative priority (-20..20), so it is mostly well behaved!

If you do the following, you will see several of these different priority systems:

Code:

ps -o pid,priority,pri,opri,nice,command

On a current Linux system, the value of pri equals 39-priority, and opri equals 60+priority.

The command top will give the 'priority'; ps -c will report 'pri', and ps -l will give 'opri'.

There are others too, and just to complicate matters, the kernel does not use the same scheduling algorithm for all processes.

corone · 10-07-2010, 05:25 AM

Thank you for your answer.
You really gave me great answer.

1 more question...

Code:

# ps -o pid,priority,nice,command

doesn't the 'priority' depend on the 'nice'?

neonsignal · 10-07-2010, 09:06 AM

Quote:

Originally Posted by corone

1 more question...
doesn't the 'priority' depend on the 'nice'?

The priority of a process doesn't necessarily relate directly to the nice value; the nice value is just a way of advising the scheduler of a relative priority.

Having said that, on my systems priority equals nice+20, but that assumption is probably not portable.