sched_setattr(2) - Linux manual page (original) (raw)
schedsetattr(2) System Calls Manual schedsetattr(2)
NAME top
sched_setattr, sched_getattr - set and get scheduling policy and
attributesLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#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)](../man2/syscall.2.html).DESCRIPTION top
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)](../man7/sched.7.html).
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)](../man7/sched.7.html) 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) */
/* For SCHED_DEADLINE */
u64 sched_runtime;
u64 sched_deadline;
u64 sched_period;
/* Utilization hints */
u32 sched_util_min;
u32 sched_util_max;
};
The fields of the _schedattr_ structure are as follows:
**size** This field should be set to the size of the structure in
bytes, as in _sizeof(struct schedattr)_. 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
_schedattr_ 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 _schedattr_
structure is increased. In the future, it could also allow
applications that know about a larger user-space _schedattr_
structure to determine whether they are running on an older
kernel that does not support the larger structure.
_schedpolicy_
This field specifies the scheduling policy, as one of the
**SCHED_*** values listed above.
_schedflags_
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)](../man2/fork.2.html) do not inherit
privileged scheduling policies. See [sched(7)](../man7/sched.7.html) 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)](../man7/signal.7.html)) 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_FLAG_UTIL_CLAMP_MIN**
**SCHED_FLAG_UTIL_CLAMP_MAX** (both since Linux 5.3)
These flags indicate that the _schedutilmin_ or
_schedutilmax_ fields, respectively, are present,
representing the expected minimum and maximum
utilization of the thread.
The utilization attributes provide the scheduler
with boundaries within which it should schedule the
thread, potentially informing its decisions
regarding task placement and frequency selection.
_schednice_
This field specifies the nice value to be set when
specifying _schedpolicy_ 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)](../man7/sched.7.html).
_schedpriority_
This field specifies the static priority to be set when
specifying _schedpolicy_ as **SCHED_FIFO** or **SCHED_RR**. The
allowed range of priorities for these policies can be
determined using [sched_get_priority_min(2)](../man2/sched%5Fget%5Fpriority%5Fmin.2.html) and
[sched_get_priority_max(2)](../man2/sched%5Fget%5Fpriority%5Fmax.2.html). For other policies, this field
must be specified as 0.
_schedruntime_
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)](../man7/sched.7.html).
_scheddeadline_
This field specifies the "Deadline" parameter for deadline
scheduling. The value is expressed in nanoseconds.
_schedperiod_
This field specifies the "Period" parameter for deadline
scheduling. The value is expressed in nanoseconds.
_schedutilmin_
_schedutilmax_ (both since Linux 5.3)
These fields specify the expected minimum and maximum
utilization, respectively. They are ignored unless their
corresponding **SCHED_FLAG_UTIL_CLAMP_MIN** or
**SCHED_FLAG_UTIL_CLAMP_MAX** is set in _schedflags_.
Utilization is a value in the range [0, 1024], representing
the percentage of CPU time used by a task when running at
the maximum frequency on the highest capacity CPU of the
system. This is a fixed point representation, where 1024
corresponds to 100%, and 0 corresponds to 0%. For example,
a 20% utilization task is a task running for 2ms every 10ms
at maximum frequency and is represented by a utilization
value of _0.2 * 1024 = 205_.
A task with a minimum utilization value larger than 0 is
more likely scheduled on a CPU with a capacity big enough
to fit the specified value. A task with a maximum
utilization value smaller than 1024 is more likely
scheduled on a CPU with no more capacity than the specified
value.
A task utilization boundary can be reset by setting its
field to **UINT32_MAX** (since Linux 5.11).
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 _schedattr_
structure as known to user space. The value must be at least as
large as the size of the initially published _schedattr_ structure,
or the call fails with the error **EINVAL**.
The retrieved scheduling attributes are placed in the fields of
the _schedattr_ structure pointed to by _attr_. The kernel sets
_attr.size_ to the size of its _schedattr_ structure.
If the caller-provided _attr_ buffer is larger than the kernel's
_schedattr_ structure, the additional bytes in the user-space
structure are not touched. If the caller-provided structure is
smaller than the kernel _schedattr_ 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.RETURN VALUE top
On success, **sched_setattr**() and **sched_getattr**() return 0. On
error, -1 is returned, and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
**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 _schedattr_ 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)](../man7/sched.7.html).
**EINVAL** _attr.schedpolicy_ is not one of the recognized policies.
**EINVAL** _attr.schedflags_ contains a flag other than
**SCHED_FLAG_RESET_ON_FORK**.
**EINVAL** _attr.schedpriority_ is invalid.
**EINVAL** _attr.schedpolicy_ is **SCHED_DEADLINE**, and the deadline
scheduling parameters in _attr_ are invalid.
**EINVAL** _attr.schedflags_ contains **SCHED_FLAG_UTIL_CLAMP_MIN** or
**SCHED_FLAG_UTIL_CLAMP_MAX**, and _attr.schedutilmin_ or
_attr.schedutilmax_ are out of bounds.
**EOPNOTSUPP**
**SCHED_FLAG_UTIL_CLAMP** was provided, but the kernel was not
built with **CONFIG_UCLAMP_TASK** support.
**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)](../man2/sched%5Fsetaffinity.2.html)).STANDARDS top
Linux.HISTORY top
Linux 3.14.NOTES top
glibc does not provide wrappers for these system calls; call them
using [syscall(2)](../man2/syscall.2.html).
**sched_setattr**() provides a superset of the functionality of
[sched_setscheduler(2)](../man2/sched%5Fsetscheduler.2.html), [sched_setparam(2)](../man2/sched%5Fsetparam.2.html), [nice(2)](../man2/nice.2.html), 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)](../man2/setpriority.2.html). Analogously, **sched_getattr**() provides a superset
of the functionality of [sched_getscheduler(2)](../man2/sched%5Fgetscheduler.2.html), [sched_getparam(2)](../man2/sched%5Fgetparam.2.html),
and (partially) [getpriority(2)](../man2/getpriority.2.html).BUGS top
In Linux versions up to 3.15, **sched_setattr**() failed with the
error **EFAULT** instead of **E2BIG** for the case described in ERRORS.
Up to Linux 5.3, **sched_getattr**() failed with the error **EFBIG** if
the in-kernel _schedattr_ structure was larger than the _size_ passed
by user space.SEE ALSO top
[chrt(1)](../man1/chrt.1.html), [nice(2)](../man2/nice.2.html), [sched_get_priority_max(2)](../man2/sched%5Fget%5Fpriority%5Fmax.2.html),
[sched_get_priority_min(2)](../man2/sched%5Fget%5Fpriority%5Fmin.2.html), [sched_getaffinity(2)](../man2/sched%5Fgetaffinity.2.html),
[sched_getparam(2)](../man2/sched%5Fgetparam.2.html), [sched_getscheduler(2)](../man2/sched%5Fgetscheduler.2.html),
[sched_rr_get_interval(2)](../man2/sched%5Frr%5Fget%5Finterval.2.html), [sched_setaffinity(2)](../man2/sched%5Fsetaffinity.2.html), [sched_setparam(2)](../man2/sched%5Fsetparam.2.html),
[sched_setscheduler(2)](../man2/sched%5Fsetscheduler.2.html), [sched_yield(2)](../man2/sched%5Fyield.2.html), [setpriority(2)](../man2/setpriority.2.html),
[pthread_getschedparam(3)](../man3/pthread%5Fgetschedparam.3.html), [pthread_setschedparam(3)](../man3/pthread%5Fsetschedparam.3.html),
[pthread_setschedprio(3)](../man3/pthread%5Fsetschedprio.3.html), [capabilities(7)](../man7/capabilities.7.html), [cpuset(7)](../man7/cpuset.7.html), [sched(7)](../man7/sched.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 schedsetattr(2)
Pages that refer to this page:uclampset(1), openat2(2), sched_setparam(2), sched_setscheduler(2), syscalls(2), capabilities(7), credentials(7), sched(7)