NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

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

NAME         top

       sched_setattr,  sched_getattr  -  set  and  get scheduling policy and
       attributes

SYNOPSIS         top

       #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         top

   sched_setattr()
       The sched_setattr() system call sets the scheduling policy and
       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 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-
       critical 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
       structure 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 structure.

              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
              applications 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
              specifying 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
              scheduling.  The value is expressed in nanoseconds.  This
              field, and the next two fields, are used only for
              SCHED_DEADLINE scheduling; 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
              scheduling.  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 outside 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         top

       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         top

       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         top

       These system calls first appeared in Linux 3.14.

CONFORMING TO         top

       These system calls are nonstandard Linux extensions.

NOTES         top

       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).
       Analogously, sched_getattr() provides a superset of the functionality
       of sched_getscheduler(2), sched_getparam(2), and (partially)
       getpriority(2).

BUGS         top

       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         top

       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         top

       This page is part of release 4.12 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)

Pages that refer to this page: sched_setparam(2)sched_setscheduler(2)syscalls(2)sched(7)