sched_setattr(2) — Linux manual page

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 the sched_attr 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 zero or more of the following flags
              that are ORed together to control scheduling behavior:

              SCHED_FLAG_RESET_ON_FORK
                     Children created by fork(2) do not inherit
                     privileged scheduling policies.  See sched(7) for
                     details.

              SCHED_FLAG_RECLAIM (since Linux 4.13)
                     This flag allows a SCHED_DEADLINE thread to reclaim
                     bandwidth unused by other real-time threads.

              SCHED_FLAG_DL_OVERRUN (since Linux 4.16)
                     This flag allows an application to get informed
                     about run-time overruns in SCHED_DEADLINE threads.
                     Such overruns may be caused by (for example) coarse
                     execution time accounting or incorrect parameter
                     assignment.  Notification takes the form of a
                     SIGXCPU signal which is generated on each overrun.

                     This SIGXCPU signal is process-directed (see
                     signal(7)) rather than thread-directed.  This is
                     probably a bug.  On the one hand, sched_setattr()
                     is being used to set a per-thread attribute.  On
                     the other hand, if the process-directed signal is
                     delivered to a thread inside the process other than
                     the one that had a run-time overrun, the
                     application has no way of knowing which thread
                     overran.

       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, the kernel will
       silently not return any values which would be stored outside the
       provided space.  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_setattr() failed with the
       error EFAULT instead of E2BIG for the case described in ERRORS.

       In Linux versions up to 5.3, sched_getattr() failed with the
       error EFBIG if the in-kernel sched_attr structure was larger than
       the size passed by user space.

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 5.10 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                          2020-11-01               SCHED_SETATTR(2)

Pages that refer to this page: openat2(2)sched_setparam(2)sched_setscheduler(2)syscalls(2)capabilities(7)credentials(7)sched(7)