sched_setattr

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;

              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 setpriority(2).

       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_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  caller's CPU affinity mask does not include all CPUs in the
              system (see sched_setaffinity(2)).

VERSIONS
       These system calls first appeared in Linux 3.14.

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_getscheduler(2), sched_getparam(2),
       sched_rr_get_interval(2), sched_setaffinity(2), sched_setscheduler(2),
       sched_setparam(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 4.04 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
       http://www.kernel.org/doc/man-pages/.

Linux                             2015-07-23                  SCHED_SETATTR(2)
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