schedutils(8) System Manager's Manual schedutils(8)NAME
sched,resched,getsched - change a process' scheduler/priority
SYNOPSISsched [-h] [-v] -r|-o|-f priority program [args, ..]
resched [-h] [-v] -r|-o|-f pid [priority]
getsched [-h] pid [pid, ...]
DESCRIPTION
schedutils are some utilities used to manipulate the scheduling and
priority of processes on *nix systems. This is realized with the func‐
tions found in sched.h, see the manpage for sched_setscheduler(2) for
more info about what's going on.
sched runs a new program under the specified scheduler and priority,
resched is used to change the scheduler and/or priority of already run‐
ning processes identified with their pid. getsched is a little utility
that prints the scheduler and priority of running processes identified
with their pid, it does not alter anything. Usually only the supe‐
ruser(root) are allowed to change scheduling parameters.
OPTIONS-h print help
-v be verbose, prints out the scheduler/priority before and after it's
changed.
-r Round Robin scheduler
-f FIFO scheduler
-o Other scheduler, this is the 'default' scheduler that normal pro‐
cesses start under.
SCHEDULING
The scheduler is the part of the kernel that decides which process that
will get the CPU next. Posix defines three diffrent policies that can
be used to decide this. See sched_setscheduler for an in-depth expla‐
nation for the platform you use.
Other the default timesharing scheduler used by normal processes. The
'Other' scheduler uses the lowest priority 0 , and it cannot be set
higher.
FIFO First In First Out must have a priority in the range 1-99 and uses
a simple fifo queue to hold the processes A process that is executed
will continue to execute until it's either preempted by a process with
higher priority, gives up the CPU (e.g. by calling sched_yield) or per‐
forms a call that blocks. Then then next process in the queue can run.
Round Robin must have a priority in the range 1-99 and are very similar
to FIFO, except it uses timesharing between the processes in the queue,
a running process will therefore give up the CPU to another process
with the same priority when it has used its time quantum.
NOTES
When a process is run under another scheduler than the default (Other)
it can never be preempted by a process with a lower priority. So, if a
process run under another scheduler uses the CPU heavily, or worse have
e.g. a bug that causes it to go in an infinite loop, no other process
might ever run and the machine might look completely locked, unless
there is an open shell running somewhere with a even higher priority,
one can execute commands and possibly kill the process.
BUGS
None known, report any you find to http://source‐
forge.net/tracker/?atid=399898&group_id=30636&func=browse
AUTHOR
Nils O. Sel�sdal <NOS@Utel.no>
SEE ALSOnice(1),renice(8),sched_setscheduler(2),sched_getscheduler(2)
July 30, 2001 schedutils(8)
