SCHED_SETATTR(2)	   Linux Programmer's Manual	      SCHED_SETATTR(2)



NAME
       sched_setattr,  sched_getattr  -	 set  and  get	scheduling  policy and
       attributes

SYNOPSIS
       #include <sched.h>

       int sched_setattr(pid_t pid, struct sched_attr *attr,
			 unsigned int flags);

       int sched_getattr(pid_t pid, struct sched_attr *attr,
			 unsigned int size, unsigned int flags);

DESCRIPTION
   sched_setattr()
       The sched_setattr() system call sets the scheduling policy and  associ-
       ated  attributes	 for  the thread whose ID is specified in pid.	If pid
       equals zero, the scheduling policy and attributes of the calling thread
       will be set.

       Currently,  Linux supports the following "normal" (i.e., non-real-time)
       scheduling policies as values that may be specified in policy:

       SCHED_OTHER   the standard round-robin time-sharing policy;

       SCHED_BATCH   for "batch" style execution of processes; and

       SCHED_IDLE    for running very low priority background jobs.

       Various "real-time" policies are also supported, for special time-crit-
       ical  applications  that	 need  precise	control	 over the way in which
       runnable threads are selected for execution.  For the  rules  governing
       when  a	process	 may  use these policies, see sched(7).	 The real-time
       policies that may be specified in policy are:

       SCHED_FIFO    a first-in, first-out policy; and

       SCHED_RR	     a round-robin policy.

       Linux also provides the following policy:

       SCHED_DEADLINE
		     a deadline scheduling policy; see sched(7) for details.

       The attr argument is a pointer to a  structure  that  defines  the  new
       scheduling policy and attributes for the specified thread.  This struc-
       ture has the following form:

	   struct sched_attr {
	       u32 size;	      /* Size of this structure */
	       u32 sched_policy;      /* Policy (SCHED_*) */
	       u64 sched_flags;	      /* Flags */
	       s32 sched_nice;	      /* Nice value (SCHED_OTHER,
					 SCHED_BATCH) */
	       u32 sched_priority;    /* Static priority (SCHED_FIFO,
					 SCHED_RR) */
	       /* Remaining fields are for SCHED_DEADLINE */
	       u64 sched_runtime;
	       u64 sched_deadline;
	       u64 sched_period;
	   };

       The fields of this structure are as follows:

       size   This field should be set to the size of the structure in	bytes,
	      as  in  sizeof(struct sched_attr).  If the provided structure is
	      smaller than the kernel structure,  any  additional  fields  are
	      assumed to be '0'.  If the provided structure is larger than the
	      kernel structure, the kernel verifies that all additional fields
	      are  0;  if  they	 are not, sched_setattr() fails with the error
	      E2BIG and updates size to contain the size of the kernel	struc-
	      ture.

	      The  above  behavior  when the size of the user-space sched_attr
	      structure does not match the size of the kernel structure allows
	      for  future  extensibility of the interface.  Malformed applica-
	      tions that pass oversize structures won't break in the future if
	      the  size	 of  the kernel sched_attr structure is increased.  In
	      the future, it could also allow applications that know  about  a
	      larger user-space sched_attr structure to determine whether they
	      are running on an older kernel that does not support the	larger
	      structure.

       sched_policy
	      This  field  specifies  the  scheduling  policy,	as  one of the
	      SCHED_* values listed above.

       sched_flags
	      This field contains flags controlling scheduling behavior.  Only
	      one  such	 flag  is currently defined: SCHED_FLAG_RESET_ON_FORK.
	      As a result of including this flag, children created by  fork(2)
	      do not inherit privileged scheduling policies.  See sched(7) for
	      details.

       sched_nice
	      This field specifies the nice value to be	 set  when  specifying
	      sched_policy as SCHED_OTHER or SCHED_BATCH.  The nice value is a
	      number in the range -20 (high priority) to +19  (low  priority);
	      see sched(7).

       sched_priority
	      This field specifies the static priority to be set when specify-
	      ing sched_policy as SCHED_FIFO or SCHED_RR.  The	allowed	 range
	      of  priorities  for  these  policies  can	 be  determined	 using
	      sched_get_priority_min(2)	 and  sched_get_priority_max(2).   For
	      other policies, this field must be specified as 0.

       sched_runtime
	      This field specifies the "Runtime" parameter for deadline sched-
	      uling.  The value is expressed in nanoseconds.  This field,  and
	      the  next	 two fields, are used only for SCHED_DEADLINE schedul-
	      ing; for further details, see sched(7).

       sched_deadline
	      This field  specifies  the  "Deadline"  parameter	 for  deadline
	      scheduling.  The value is expressed in nanoseconds.

       sched_period
	      This  field specifies the "Period" parameter for deadline sched-
	      uling.  The value is expressed in nanoseconds.

       The flags argument is provided to allow for future  extensions  to  the
       interface; in the current implementation it must be specified as 0.

   sched_getattr()
       The  sched_getattr()  system call fetches the scheduling policy and the
       associated attributes for the thread whose ID is specified in pid.   If
       pid  equals  zero,  the scheduling policy and attributes of the calling
       thread will be retrieved.

       The size argument should be set to the size of the sched_attr structure
       as  known  to  user  space.  The value must be at least as large as the
       size of the initially published sched_attr structure, or the call fails
       with the error EINVAL.

       The  retrieved  scheduling  attributes  are placed in the fields of the
       sched_attr structure pointed to by attr.	 The kernel sets attr.size  to
       the size of its sched_attr structure.

       If  the	caller-provided	 attr  buffer  is  larger  than	 the  kernel's
       sched_attr structure, the additional bytes in the user-space  structure
       are  not touched.  If the caller-provided structure is smaller than the
       kernel sched_attr structure and the kernel needs to return values  out-
       side  the  provided  space, sched_getattr() fails with the error E2BIG.
       As with sched_setattr(), these semantics allow for future extensibility
       of the interface.

       The  flags  argument  is provided to allow for future extensions to the
       interface; in the current implementation it must be specified as 0.

RETURN VALUE
       On success, sched_setattr() and sched_getattr() return 0.  On error, -1
       is returned, and errno is set to indicate the cause of the error.

ERRORS
       sched_getattr()	and  sched_setattr()  can  both fail for the following
       reasons:

       EINVAL attr is NULL; or pid is negative; or flags is not zero.

       ESRCH  The thread whose ID is pid could not be found.

       In addition, sched_getattr() can fail for the following reasons:

       E2BIG  The buffer specified by size and attr is too small.

       EINVAL size is invalid; that is, it is smaller than the initial version
	      of the sched_attr structure (48 bytes) or larger than the system
	      page size.

       In addition, sched_setattr() can fail for the following reasons:

       E2BIG  The buffer specified by size and attr is larger than the	kernel
	      structure, and one or more of the excess bytes is nonzero.

       EBUSY  SCHED_DEADLINE admission control failure, see sched(7).

       EINVAL attr.sched_policy	  is  not  one	of  the	 recognized  policies;
	      attr.sched_flags	   contains	a     flag     other	  than
	      SCHED_FLAG_RESET_ON_FORK;	 or attr.sched_priority is invalid; or
	      attr.sched_policy is SCHED_DEADLINE and the deadline  scheduling
	      parameters in attr are invalid.

       EPERM  The caller does not have appropriate privileges.

       EPERM  The  CPU	affinity  mask of the thread specified by pid does not
	      include all CPUs in the system (see sched_setaffinity(2)).

VERSIONS
       These system calls first appeared in Linux 3.14.

CONFORMING TO
       These system calls are nonstandard Linux extensions.

NOTES
       sched_setattr()	provides  a   superset	 of   the   functionality   of
       sched_setscheduler(2),  sched_setparam(2), nice(2), and (other than the
       ability to set the priority of all processes belonging to  a  specified
       user  or	 all  processes	 in a specified group) setpriority(2).	Analo-
       gously, sched_getattr() provides a superset  of	the  functionality  of
       sched_getscheduler(2),  sched_getparam(2),  and	(partially)  getprior-
       ity(2).

BUGS
       In Linux versions up to 3.15, sched_settattr() failed  with  the	 error
       EFAULT instead of E2BIG for the case described in ERRORS.

SEE ALSO
       chrt(1), nice(2), sched_get_priority_max(2), sched_get_priority_min(2),
       sched_getaffinity(2), sched_getparam(2), sched_getscheduler(2),
       sched_rr_get_interval(2), sched_setaffinity(2), sched_setparam(2),
       sched_setscheduler(2), sched_yield(2), setpriority(2),
       pthread_getschedparam(3), pthread_setschedparam(3),
       pthread_setschedprio(3), capabilities(7), cpuset(7), sched(7)

COLOPHON
       This page is part of release 4.10 of the Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-10-08		      SCHED_SETATTR(2)