Difference between revisions of "Process Niceness"
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| + | 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 | ||
| + | |||
| + | Lowest level of niceness (lower means more favorable) you can define is determined by limits.conf | ||
| + | |||
| + | 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 7: | Line 27: | ||
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. | ||
| + | |||
| + | Example 1: As a non-privileged user we shall launch Discord client at the least important priority (the nicest) | ||
| + | nice -n20 /usr/share/discord/Discord | ||
| + | Now about everything else will have priority to the CPU than does Discord. | ||
| + | |||
| + | 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. | ||
| + | While Running | ||
| + | You can change the priority of the process already running. Example: | ||
| + | sudo renice -n -10 14566 | ||
| + | This process has increased process priority. The process was originally executed without root. The process is running as a non privileged user, however, it is necessary to use root permissions to elevate the priority higher than 0. The process itself remains non privileged. | ||
[[Category:Computer_Technology]] | [[Category:Computer_Technology]] | ||
[[Category:Linux]] | [[Category:Linux]] | ||
Latest revision as of 09:36, 29 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
Lowest level of niceness (lower means more favorable) you can define is determined by limits.conf
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.
Example 1: As a non-privileged user we shall launch Discord client at the least important priority (the nicest)
nice -n20 /usr/share/discord/Discord
Now about everything else will have priority to the CPU than does Discord.
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.
While Running
You can change the priority of the process already running. Example:
sudo renice -n -10 14566
This process has increased process priority. The process was originally executed without root. The process is running as a non privileged user, however, it is necessary to use root permissions to elevate the priority higher than 0. The process itself remains non privileged.
