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       sched_setscheduler,   sched_getscheduler   -  set  and  get  scheduling


       #include <sched.h>

       int sched_setscheduler(pid_t pid, int policy,
                              const struct sched_param *param);

       int sched_getscheduler(pid_t pid);


       The sched_setscheduler() system call sets both  the  scheduling  policy
       and  parameters  for  the  thread whose ID is specified in pid.  If pid
       equals zero, the scheduling policy and parameters of the calling thread
       will be set.

       The scheduling parameters are specified in the param argument, which is
       a pointer to a structure of the following form:

           struct sched_param {
               int sched_priority;

       In the current implementation, the structure contains only  one  field,
       sched_priority.   The  interpretation  of param depends on the selected

       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.

       For each of the above policies, param->sched_priority must be 0.

       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.

       For  each  of  the  above  policies,  param->sched_priority specifies a
       scheduling priority for the thread.  This is  a  number  in  the  range
       returned       by       calling      sched_get_priority_min(2)      and
       sched_get_priority_max(2) with the specified policy.  On  Linux,  these
       system calls return, respectively, 1 and 99.

       Since  Linux 2.6.32, the SCHED_RESET_ON_FORK flag can be ORed in policy
       when calling sched_setscheduler().  As a result of including this flag,
       children  created  by  fork(2)  do  not  inherit  privileged scheduling
       policies.  See sched(7) for details.

       sched_getscheduler() returns  the  current  scheduling  policy  of  the
       thread  identified  by  pid.   If  pid  equals  zero, the policy of the
       calling thread will be retrieved.


       On   success,   sched_setscheduler()   returns   zero.    On   success,
       sched_getscheduler()  returns  the policy for the thread (a nonnegative
       integer).   On  error,  both  calls  return  -1,  and  errno   is   set


       EINVAL Invalid arguments: pid is negative or param is NULL.

       EINVAL (sched_setscheduler())  policy  is  not  one  of  the recognized

       EINVAL (sched_setscheduler())  param  does  not  make  sense  for   the
              specified policy.

       EPERM  The calling thread does not have appropriate privileges.

       ESRCH  The thread whose ID is pid could not be found.


       POSIX.1-2001,  POSIX.1-2008  (but see BUGS below).  The SCHED_BATCH and
       SCHED_IDLE policies are Linux-specific.


       Further details of the semantics of  all  of  the  above  "normal"  and
       "real-time" scheduling policies can be found in sched(7).

       POSIX  systems  on  which sched_setscheduler() and sched_getscheduler()
       are available define _POSIX_PRIORITY_SCHEDULING in <unistd.h>.

       POSIX.1 does not detail the permissions  that  an  unprivileged  thread
       requires in order to call sched_setscheduler(), and details vary across
       systems.  For example, the Solaris 7 manual page says that the real  or
       effective user ID of the caller must match the real user ID or the save
       set-user-ID of the target.

       The scheduling policy and parameters are in fact per-thread  attributes
       on Linux.  The value returned from a call to gettid(2) can be passed in
       the argument pid.  Specifying pid as 0 will operate on  the  attributes
       of  the  calling  thread, and passing the value returned from a call to
       getpid(2) will operate on the attributes of  the  main  thread  of  the
       thread  group.   (If  you  are  using  the  POSIX threads API, then use
       pthread_setschedparam(3),         pthread_getschedparam(3),         and
       pthread_setschedprio(3), instead of the sched_*(2) system calls.)


       POSIX.1  says  that  on success, sched_setscheduler() should return the
       previous  scheduling  policy.   Linux  sched_setscheduler()  does   not
       conform to this requirement, since it always returns 0 on success.


       chrt(1), nice(2), sched_get_priority_max(2), sched_get_priority_min(2),
       sched_getaffinity(2), sched_getattr(2), sched_getparam(2),
       sched_rr_get_interval(2), sched_setaffinity(2), sched_setattr(2),
       sched_setparam(2), sched_yield(2), setpriority(2), capabilities(7),
       cpuset(7), sched(7)


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