установить и получить политику / параметры планирования (set and get scheduling policy/parameters)
Имя (Name)
sched_setscheduler, sched_getscheduler - set and get scheduling
policy/parameters
Синопсис (Synopsis)
#include <sched.h>
int sched_setscheduler(pid_t pid, int policy,
const struct sched_param *param);
int sched_getscheduler(pid_t pid);
Описание (Description)
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 policy.
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.
Возвращаемое значение (Return value)
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 to indicate the error.
Ошибки (Error)
EINVAL Invalid arguments: pid is negative or param is NULL.
EINVAL (sched_setscheduler()) policy is not one of the recognized
policies.
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.
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008 (but see BUGS below). The SCHED_BATCH
and SCHED_IDLE policies are Linux-specific.
Примечание (Note)
Further details of the semantics of all of the above "normal" and
"real-time" scheduling policies can be found in the sched(7)
manual page. That page also describes an additional policy,
SCHED_DEADLINE, which is settable only via sched_setattr(2).
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.)
Ошибки (баги) (Bugs)
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.
Смотри также (See also)
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)
