schedsetscheduler(2)                                    schedsetscheduler(2)



NAME
     schedsetscheduler - set the scheduling policy of a process

C SYNOPSIS
     #include <sched.h>

     int schedsetscheduler (pidt pid, int policy,

     const struct schedparam *param);


DESCRIPTION

     The schedsetscheduler system call is used to set the scheduling policy

     and related parameters for the process specified by pid.  If pid is set

     to zero, then the scheduling policy and parameters of the calling process

     will be affected.


     The policy parameter is used to select one of the following scheduling

     policies:


     SCHEDFIFO

             The first-in-first-out policy schedules processes according to

             their assigned priority values. The highest priority process is

             guaranteed control of the processor until it willingly yields the

             processor or blocks on a contended resource. If there is more

             than one runnable highest priority process, the highest priority

             process waiting the longest is granted control of the processor.

             A running process is preempted when a higher priority process

             becomes runnable.


     SCHEDRR

             The round-robin scheduling policy schedules processes according

             to their assigned priority values. The highest priority process

             is guaranteed control of the processor until it: willingly yields

             the processor, blocks on a contended resource, or exceeds its

             time quantum. If there is more than one runnable highest priority

             process, the highest priority process waiting the longest is

             granted control of the processor. When a process exceeds its time

             quantum it yields the processor and awaits rescheduling.  A

             running process is preempted when a higher priority process

             becomes runnable.


     Note that SCHED_FIFO and SCHED_RR processes are of higher priority than

     all other processes in the system.  Because of this, such a process may

     deadlock the system if it enters an infinite loop.  Further note, that

     the scheduling policy and priority are inherited across a fork and that

     the scheduling policy is shared by all members of a share group (see

     sproc(2)).


     SCHEDTS

             The SCHED_TS scheduling policy is a basic timeshare scheduling

             policy.  All SCHED_TS processes acquire CPU resources in

             proportion to their priority or nice value.  Processes aquire the

             processor for a time quantum, the length of which is returned via

             the sched_rr_get_interval(2) system call.



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schedsetscheduler(2)                                    schedsetscheduler(2)



     SCHEDOTHER
             The SCHED_OTHER scheduling policy is equivalent to the SCHED_TS
             policy and allows a program to indicate that it no longer needs a
             real-time scheduling policy in a portable manner.

     The parameters of the selected policy are specified by the parameter
     structure at address param.

     The priority of the target process may be modified by setting the desired
     priority value in the sched_priority field of the param structure.

     Unlike IRIX 6.2 and previous releases, processes having a higher
     numerical priority value are more important than processes having a lower
     numerical priority value.  Specified priorities remain fixed, unless
     explicitly changed in the future, and are not affected by priority aging
     schemes.

     The priority range for these scheduling policies may be obtained via the
     schedgetprioritymin(2) and schedgetprioritymax(2) function calls.
     However, arbitrary priority values should not be used.  Developers must
     consider the needs of the application and how it should interact with the
     rest of the system, before selecting a real-time priority.  For more
     information, see the "Real-Time Priority Band" section of realtime(5).

     Runnable processes scheduled with real-time policies are always granted
     processor control ahead of timeshare processes, regardless of priority.

     The calling process must have superuser permissions to successfully
     execute schedsetscheduler.

     If the process specified by pid is currently executing or is in a
     runnable state, schedsetscheduler causes the process to be rescheduled
     in accordance with its priority.

     If pid refers to a POSIX thread process [see pthreads(3P)] then this call
     changes the scheduling policy and related parameters that are shared by
     process scope threads.

     schedsetscheduler will fail if one or more of the following are true:

     [EINVAL]       The policy argument does not represent a valid posix
                    scheduling policy.

     [EINVAL]       One of the specified parameters at address param are out
                    of range or scope.

     [EPERM]        The calling process does not have superuser permissions.

     [ESRCH]        The process specified by pid does not exist.






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schedsetscheduler(2)                                    schedsetscheduler(2)



SEE ALSO
     realtime(5), sched_getparam(2), sched_setparam(2), sched_getscheduler(2),
     sched_yield(2), sched_get_priority_max(2), sched_get_priority_min(2),
     sched_rr_get_interval(2), pthreads(5)

DIAGNOSTICS
     Upon successful completion, schedsetscheduler returns the previous
     scheduling policy value of the process pid.

     Upon failure, a value of -1 is returned to the calling process and errno
     is set to indicate the error.












































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