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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 (consult 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  speci-
       fied  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 appro-
       priate 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  argu-
       ment  shall  be any integer within the inclusive priority range for the
       sporadic server policy. The sched_ss_repl_period and sched_ss_init_bud-
       get  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 rep-
       resent 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  mem-
       bers  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 implementa-
       tion-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 parame-
       ters 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 .

IEEE/The Open Group                  2003                   SCHED_SETPARAM(3P)