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Linux 2.6 - man page for sched_setparam (linux section 3posix)

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

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 spec-
       ified 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 pri-
       ority 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 con-
       tention 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 parame-
	  ters 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-sched-
       uled entities for the system contention scope threads shall not be affected by these func-
       tions.

       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 com-
       pletes 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 vol-
       ume 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				SCHED_SETPARAM(P)


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