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sched_getattr(2) - phpMan
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, const struct sched_attr *attr,
unsigned int flags);
int sched_getattr(pid_t pid, const 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 execu‐
tion. 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 pri‐
ority) to +19 (low priority); see setpriority(2).
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 schedul‐
ing 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.
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 caller's CPU affinity mask 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 pro‐
cesses belonging to a specified user or all processes in a specified group) setprior‐
ity(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_settattr() failed with the error EFAULT instead of
E2BIG for the case described in ERRORS.
SEE ALSO
chrt(1), nice(2), sched_get_priority_max(2), sched_get_priority_min(2),
sched_getaffinity(2), sched_getscheduler(2), sched_getparam(2), sched_rr_get_interval(2),
sched_setaffinity(2), sched_setscheduler(2), sched_setparam(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 3.74 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 http://www.kernel.org/doc/man-pages/.
Linux 2014-10-02 SCHED_SETATTR(2)
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