SCHED_SETPARAM(3P)                                  POSIX Programmer's Manual                                 SCHED_SETPARAM(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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  imple-
       mentation-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 sched-
       uled 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.  How-
          ever,  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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                            SCHED_SETPARAM(3P)