NAME

       sched_setscheduler - set scheduling policy and parameters (REALTIME)

SYNOPSIS

       #include <sched.h>

       int sched_setscheduler(pid_t pid, int policy,
              const struct sched_param *param);

DESCRIPTION

       The   sched_setscheduler()  function  shall  set  the  scheduling  policy  and  scheduling
       parameters of the process specified by pid to policy and the parameters specified  in  the
       sched_param  structure  pointed to by param, respectively. The value of the sched_priority
       member in the sched_param structure shall be any integer  within  the  inclusive  priority
       range for the scheduling policy specified by policy.  If the value of pid is negative, the
       behavior of the sched_setscheduler() function is unspecified.

       The possible values for the policy parameter are defined in the <sched.h> header.

       If a process specified by pid exists, and if  the  calling  process  has  permission,  the
       scheduling  policy and scheduling parameters shall be set for the process whose process ID
       is equal to pid.

       If pid is zero, the scheduling policy and scheduling  parameters  shall  be  set  for  the
       calling process.

       The  conditions  under  which  one  process  has  the  appropriate privilege to change the
       scheduling parameters of another process are implementation-defined.

       Implementations may require that the requesting process have permission  to  set  its  own
       scheduling  parameters  or  those of another process. Additionally, implementation-defined
       restrictions may apply as to the appropriate privileges required to  set  a  process'  own
       scheduling policy, or another process' scheduling policy, to a particular value.

       The sched_setscheduler() function shall be considered successful if it succeeds in setting
       the scheduling policy and scheduling parameters of the process specified  by  pid  to  the
       values specified by policy and the structure pointed to by param, respectively.

       If the scheduling policy specified by policy is SCHED_SPORADIC, the value specified by the
       sched_ss_low_priority member of the  param  argument  shall  be  any  integer  within  the
       inclusive  priority  range  for  the  sporadic server policy. The sched_ss_repl_period and
       sched_ss_init_budget members of the param argument shall  represent  the  time  parameters
       used   by   the   sporadic   server   scheduling   policy  for  the  target  process.  The
       sched_ss_max_repl member of the param argument  shall  represent  the  maximum  number  of
       replenishments  that  are  allowed  to be pending simultaneously for the process scheduled
       under this scheduling policy.

       The specified sched_ss_repl_period shall  be  greater  than  or  equal  to  the  specified
       sched_ss_init_budget  for  the  function to succeed; if it is not, then the function shall
       fail.

       The value of sched_ss_max_repl shall be within the inclusive range [1, {SS_REPL_MAX}]  for
       the function to succeed; if not, the function shall fail.

       If  the  scheduling  policy  specified  by  policy  is  either SCHED_FIFO or SCHED_RR, the
       sched_ss_low_priority, sched_ss_repl_period, and sched_ss_init_budget members of the param
       argument shall have no effect on the scheduling behavior.

       The  effect  of  this  function  on  individual  threads  is  dependent  on the scheduling
       contention scope of the threads:

        * For threads with system scheduling contention scope,  these  functions  shall  have  no
          effect on their scheduling.

        * For  threads  with  process scheduling contention scope, the threads' scheduling policy
          and associated parameters shall not be  affected.  However,  the  scheduling  of  these
          threads  with  respect to threads in other processes may be dependent on the scheduling
          parameters of their process, which are governed using these functions.

       If an implementation supports a two-level scheduling model in which  library  threads  are
       multiplexed  on  top  of  several  kernel-scheduled  entities, then the underlying kernel-
       scheduled entities for the system contention scope threads shall not be affected by  these
       functions.

       The  underlying  kernel-scheduled  entities for the process contention scope threads shall
       have their scheduling policy and associated scheduling parameters changed  to  the  values
       specified  in policy and param, respectively. Kernel-scheduled entities for use by process
       contention scope threads that are created after this call completes  shall  inherit  their
       scheduling policy and associated scheduling parameters from the process.

       This  function  is  not  atomic with respect to other threads in the process.  Threads may
       continue to execute while this function call is in the process of changing the  scheduling
       policy  and  associated scheduling parameters for the underlying kernel-scheduled entities
       used by the process contention scope threads.

RETURN VALUE

       Upon successful completion, the function shall return the former scheduling policy of  the
       specified  process.  If  the sched_setscheduler() function fails to complete successfully,
       the policy and scheduling parameters shall remain unchanged, and the function shall return
       a value of -1 and set errno to indicate the error.

ERRORS

       The sched_setscheduler() function shall fail if:

       EINVAL The  value  of  the  policy  parameter is invalid, or one or more of the parameters
              contained in param is outside the valid range for the specified scheduling policy.

       EPERM  The requesting process does not have permission  to  set  either  or  both  of  the
              scheduling parameters or the scheduling policy of the specified process.

       ESRCH  No process can be found corresponding to that specified by pid.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       sched_getparam()  ,  sched_getscheduler() , sched_setparam() , the Base Definitions volume
       of IEEE Std 1003.1-2001, <sched.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .