установить и получить политику и атрибуты планирования (set and get scheduling policy and attributes)
Имя (Name)
sched_setattr, sched_getattr - set and get scheduling policy and
attributes
Синопсис (Synopsis)
#include <sched.h> /* Definition of SCHED_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS_sched_setattr, pid_t pid, struct sched_attr *attr,
unsigned int flags);
int syscall(SYS_sched_getattr, pid_t pid, struct sched_attr *attr,
unsigned int size, unsigned int flags);
Note: glibc provides no wrappers for these system calls,
necessitating the use of syscall(2).
Описание (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.
Возвращаемое значение (Return value)
On success, sched_setattr() and sched_getattr() return 0. On
error, -1 is returned, and errno is set to indicate the error.
Ошибки (Error)
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)).
Версии (Versions)
These system calls first appeared in Linux 3.14.
Стандарты (Conforming to)
These system calls are nonstandard Linux extensions.
Примечание (Note)
Glibc does not provide wrappers for these system calls; call them
using syscall(2).
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).
Ошибки (баги) (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.
Смотри также (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)
