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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
SCHED_SETATTR(2) Linux Programmer's Manual SCHED_SETATTR(2)
sched_setattr, sched_getattr - set and get scheduling policy and
attributes
#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);
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 flags controlling scheduling behavior.
Only one such flag is currently defined:
SCHED_FLAG_RESET_ON_FORK. As a result of including this flag,
children created by fork(2) do not inherit privileged
scheduling policies. See sched(7) for details.
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.
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.
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)).
These system calls first appeared in Linux 3.14.
These system calls are nonstandard Linux extensions.
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).
In Linux versions up to 3.15, sched_settattr() failed with the error
EFAULT instead of E2BIG for the case described in ERRORS.
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)
This page is part of release 4.12 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 2016-10-08 SCHED_SETATTR(2)
Pages that refer to this page: sched_setparam(2), sched_setscheduler(2), syscalls(2), sched(7)