07-14-2009
Quote:
that the operating system corrects the priorities as the processes need cpu
Actually, this is true, but nice priorities still come into play. The longer a process has been running and consuming CPU resources, the lower a priority it gets. The more time it's been in the run queue without having had a chance to execute, the higher priority it gets. These mechanisms are meant to ensure fairness and reduce "starvation". Nice affects starting priorities, and only after a very long runtime, will the nice level for a particular process become irrelevant.
At any rate, task scheduling is OS-dependent. The Linux 2.6 kernel uses something called the
Completely Fair Scheduler. From the author, this quote might be relevant:
Quote:
the CFS scheduler has a much stronger handling of nice levels and SCHED_BATCH: both types of workloads should be isolated much more agressively than under the vanilla [ie, than the standard Linux scheduler] scheduler.
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nice(1) General Commands Manual nice(1)
Name
nice, nohup - execute a command at a lower priority
Syntax
nice [-number] command [arguments]
nohup command [arguments]
Description
The command executes command with low scheduling priority (Bourne Shell only). If the number argument is present, the priority is incre-
mented (higher numbers mean lower priorities) by that amount up to a limit of 20. The default number is 10.
The super-user may run commands with priority higher than normal by using a negative priority, for example, `--10'.
The command executes command immune to hangup and terminate signals from the controlling terminal. The priority is incremented by 5. The
command should be invoked from the shell with an ampersand (&) in order to prevent it from responding to interrupts by or stealing the
input from the next person who logs in on the same terminal. The syntax of is also different.
Options
-number Increments the priority by a specified number up to a limit of 20. The default is 10.
Restrictions
The and commands are particular to If you use then commands executed with an ampersand (&) are automatically immune to hangup signals while
in the background. There is a built-in command which provides immunity from terminate, but it does not redirect output to nohup.out.
The command is built into with a slightly different syntax than described here. The form ``nice +10'' nices to positive nice, and ``nice
-10'' can be used by the superuser to give a process more of the processor.
Diagnostics
The command returns the exit status of the subject command.
Files
nohup.out standard output and standard error file under nohup
See Also
csh(1), getpriority(2), renice(8)
nice(1)