sched_getattr

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 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
       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_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
       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 5.10 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)