sched_setattr

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
       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 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 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
       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).
       Analogously, sched_getattr() provides a superset of the functionality
       of sched_getscheduler(2), sched_getparam(2), and (partially)
       getpriority(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 5.03 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                             2019-03-06                  SCHED_SETATTR(2)