NAME

       sched_setparam - set scheduling parameters (REALTIME)

SYNOPSIS

       #include <sched.h>

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

DESCRIPTION

       The  sched_setparam() function shall set the scheduling parameters of the process specified by pid to the
       values specified by the sched_param structure pointed to by  param.   The  value  of  the  sched_priority
       member  in  the  sched_param  structure  shall be any integer within the inclusive priority range for the
       current scheduling policy of the process specified by pid.  Higher  numerical  values  for  the  priority
       represent  higher  priorities.  If  the  value  of  pid is negative, the behavior of the sched_setparam()
       function is unspecified.

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

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

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

       Implementations may require the requesting process to have the  appropriate  privilege  to  set  its  own
       scheduling parameters or those of another process.

       The  target  process, whether it is running or not running, shall be moved to the tail of the thread list
       for its priority.

       If the priority of the process specified by the pid argument is  set  higher  than  that  of  the  lowest
       priority  running  process and if the specified process is ready to run, the process specified by the pid
       argument  shall  preempt  a  lowest  priority  running  process.  Similarly,  if  the   process   calling
       sched_setparam() sets its own priority lower than that of one or more other non-empty process lists, then
       the process that is the head of the highest priority list shall also preempt the calling  process.  Thus,
       in either case, the originating process might not receive notification of the completion of the requested
       priority change until the higher priority process has executed.

       If the  scheduling  policy  of  the  target  process  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 to be 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  of  the   target   process   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. If the scheduling policy of this process  is  not  SCHED_FIFO,
       SCHED_RR,  or SCHED_SPORADIC, the effects of these members are implementation-defined; this case includes
       the SCHED_OTHER policy.

       If the current scheduling policy for the process specified by pid  is  not  SCHED_FIFO,  SCHED_RR,     or
       SCHED_SPORADIC,   the result is implementation-defined; this case includes the SCHED_OTHER policy.

       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 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 parameters changed to the value specified in  param.  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 for the underlying
       kernel-scheduled entities used by the process contention scope threads.

RETURN VALUE

       If successful, the sched_setparam() function shall return zero.

       If the call to sched_setparam() is unsuccessful, the priority shall remain unchanged,  and  the  function
       shall return a value of -1 and set errno to indicate the error.

ERRORS

       The sched_setparam() function shall fail if:

       EINVAL One or more of the requested scheduling parameters is outside the range defined for the scheduling
              policy of the specified pid.

       EPERM  The requesting process does not have permission to set the scheduling parameters for the specified
              process, or does not have the appropriate privilege to invoke sched_setparam().

       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_setscheduler()  ,  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 .