Difference between revisions of "Process Niceness"

From Free Knowledge Base- The DUCK Project: information for everyone
Jump to: navigation, search
m
Line 5: Line 5:
 
renice - change process priority real time.
 
renice - change process priority real time.
  
 +
A kernel scheduler is a unit of the kernel that determines the most suitable process out of all runnable processes to execute next. 
  
 +
There are a total of 140 priorities and two distinct priority ranges implemented in Linux. The first one is a nice value (niceness) which ranges from -20 (highest priority value) to 19 (lowest priority value) and the default is 0.
 +
* niceness of -20 gives the process the most priority
 +
* niceness of 19 gives the process the least priority
  
 +
Total number of priorities = 140
 +
Real time priority range(PR or PRI):  0 to 99
 +
User space priority range: 100 to 139
  
 
=== check nice level setting ===
 
=== check nice level setting ===
 +
One way
 +
ps -eo pid,ppid,ni,comm
 +
 
This will list the process ID, the nice level, and the actual command.
 
This will list the process ID, the nice level, and the actual command.
 
  ps ax -o pid,ni,cmd
 
  ps ax -o pid,ni,cmd
Line 15: Line 25:
 
  sudo apt install htop
 
  sudo apt install htop
  
 +
=== changing the program priority ===
 +
nice runs commands at increased priority, renice can raise or lower but works for processes that are already running.
 +
 +
*If no value is provided, nice sets a priority of 10 by default.
 +
*A command or program run without nice defaults to a priority of zero.
 +
*Only root can run a command or program with increased or high priority.
 +
*Normal users can only run a command or program with low priority.
 +
 +
 +
you can use the ionice command to start the process with low io priority:
 +
nice -n18 ionice -c3 /path/to/mydaemon
 +
 +
How to renice all threads (and children) of one process
  
 +
The kernel only handles "runnable entities", that is, something which can be run and scheduled.  A thread, is just a kind of process that shares (at least) memory space and signal handlers with another one.
  
  

Revision as of 20:45, 27 May 2020

NICE and RENICE

nice - set process scheduling priority

renice - change process priority real time.

A kernel scheduler is a unit of the kernel that determines the most suitable process out of all runnable processes to execute next.

There are a total of 140 priorities and two distinct priority ranges implemented in Linux. The first one is a nice value (niceness) which ranges from -20 (highest priority value) to 19 (lowest priority value) and the default is 0.

  • niceness of -20 gives the process the most priority
  • niceness of 19 gives the process the least priority
Total number of priorities = 140
Real time priority range(PR or PRI):  0 to 99 
User space priority range: 100 to 139

check nice level setting

One way

ps -eo pid,ppid,ni,comm

This will list the process ID, the nice level, and the actual command.

ps ax -o pid,ni,cmd

Using the htop command will show nice level. This requires installation. For Ubuntu/Mint:

sudo apt install htop

changing the program priority

nice runs commands at increased priority, renice can raise or lower but works for processes that are already running.

  • If no value is provided, nice sets a priority of 10 by default.
  • A command or program run without nice defaults to a priority of zero.
  • Only root can run a command or program with increased or high priority.
  • Normal users can only run a command or program with low priority.


you can use the ionice command to start the process with low io priority:

nice -n18 ionice -c3 /path/to/mydaemon

How to renice all threads (and children) of one process

The kernel only handles "runnable entities", that is, something which can be run and scheduled. A thread, is just a kind of process that shares (at least) memory space and signal handlers with another one.