.\" Copyright (C) 2014 Michael Kerrisk <mtk.manpages@gmail.com>

.\" and Copyright (C) 2014 Peter Zijlstra <peterz@infradead.org>

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.TH SCHED_SETATTR 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

sched_setattr, sched_getattr \-

set and get scheduling policy and attributes

.SH SYNOPSIS

.nf

.B #include <sched.h>

.PP

.BI "int sched_setattr(pid_t " pid ", struct sched_attr *" attr ,

.BI "                  unsigned int " flags );

.PP

.BI "int sched_getattr(pid_t " pid ", struct sched_attr *" attr ,

.BI "                  unsigned int " size ", unsigned int " flags );

.fi

.\" FIXME . Add feature test macro requirements

.SH DESCRIPTION

.SS sched_setattr()

The

.BR sched_setattr ()

system call sets the scheduling policy and

associated attributes for the thread whose ID is specified in

.IR pid .

If

.I pid

equals zero,

the scheduling policy and attributes of the calling thread will be set.

.PP

Currently, Linux supports the following "normal"

(i.e., non-real-time) scheduling policies as values that may be specified in

.IR policy :

.TP 14

.BR SCHED_OTHER

the standard round-robin time-sharing policy;

.\" In the 2.6 kernel sources, SCHED_OTHER is actually called

.\" SCHED_NORMAL.

.TP

.BR SCHED_BATCH

for "batch" style execution of processes; and

.TP

.BR SCHED_IDLE

for running

.I very

low priority background jobs.

.PP

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

.BR sched (7).

The real-time policies that may be specified in

.IR policy

are:

.TP 14

.BR SCHED_FIFO

a first-in, first-out policy; and

.TP

.BR SCHED_RR

a round-robin policy.

.PP

Linux also provides the following policy:

.TP 14

.B SCHED_DEADLINE

a deadline scheduling policy; see

.BR sched (7)

for details.

.PP

The

.I 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:

.PP

.in +4n

.EX

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;

};

.EE

.in

.PP

The fields of this structure are as follows:

.TP

.B size

This field should be set to the size of the structure in bytes, as in

.IR "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,

.BR sched_setattr ()

fails with the error

.BR E2BIG

and updates

.I size

to contain the size of the kernel structure.

.IP

The above behavior when the size of the user-space

.I 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

.I sched_attr

structure is increased.

In the future,

it could also allow applications that know about a larger user-space

.I sched_attr

structure to determine whether they are running on an older kernel

that does not support the larger structure.

.TP

.I sched_policy

This field specifies the scheduling policy, as one of the

.BR SCHED_*

values listed above.

.TP

.I sched_flags

This field contains flags controlling scheduling behavior.

Only one such flag is currently defined:

.BR SCHED_FLAG_RESET_ON_FORK .

As a result of including this flag, children created by

.BR fork (2)

do not inherit privileged scheduling policies.

See

.BR sched (7)

for details.

.TP

.I sched_nice

This field specifies the nice value to be set when specifying

.IR sched_policy

as

.BR SCHED_OTHER

or

.BR SCHED_BATCH .

The nice value is a number in the range \-20 (high priority)

to +19 (low priority); see

.BR sched (7).

.TP

.I sched_priority

This field specifies the static priority to be set when specifying

.IR sched_policy

as

.BR SCHED_FIFO

or

.BR SCHED_RR .

The allowed range of priorities for these policies can be determined using

.BR sched_get_priority_min (2)

and

.BR sched_get_priority_max (2).

For other policies, this field must be specified as 0.

.TP

.I 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

.BR SCHED_DEADLINE

scheduling; for further details, see

.BR sched (7).

.TP

.I sched_deadline

This field specifies the "Deadline" parameter for deadline scheduling.

The value is expressed in nanoseconds.

.TP

.I sched_period

This field specifies the "Period" parameter for deadline scheduling.

The value is expressed in nanoseconds.

.PP

The

.I flags

argument is provided to allow for future extensions to the interface;

in the current implementation it must be specified as 0.

.\"

.\"

.SS sched_getattr()

The

.BR sched_getattr ()

system call fetches the scheduling policy and the

associated attributes for the thread whose ID is specified in

.IR pid .

If

.I pid

equals zero,

the scheduling policy and attributes of the calling thread

will be retrieved.

.PP

The

.I size

argument should be set to the size of the

.I sched_attr

structure as known to user space.

The value must be at least as large as the size of the initially published

.I sched_attr

structure, or the call fails with the error

.BR EINVAL .

.PP

The retrieved scheduling attributes are placed in the fields of the

.I sched_attr

structure pointed to by

.IR attr .

The kernel sets

.I attr.size

to the size of its

.I sched_attr

structure.

.PP

If the caller-provided

.I attr

buffer is larger than the kernel's

.I sched_attr

structure,

the additional bytes in the user-space structure are not touched.

If the caller-provided structure is smaller than the kernel

.I sched_attr

structure and the kernel needs to return values outside the provided space,

.BR sched_getattr ()

fails with the error

.BR E2BIG .

As with

.BR sched_setattr (),

these semantics allow for future extensibility of the interface.

.PP

The

.I flags

argument is provided to allow for future extensions to the interface;

in the current implementation it must be specified as 0.

.SH RETURN VALUE

On success,

.BR sched_setattr ()

and

.BR sched_getattr ()

return 0.

On error, \-1 is returned, and

.I errno

is set to indicate the cause of the error.

.SH ERRORS

.BR sched_getattr ()

and

.BR sched_setattr ()

can both fail for the following reasons:

.TP

.B EINVAL

.I attr

is NULL; or

.I pid

is negative; or

.I flags

is not zero.

.TP

.B ESRCH

The thread whose ID is

.I pid

could not be found.

.PP

In addition,

.BR sched_getattr ()

can fail for the following reasons:

.TP

.B E2BIG

The buffer specified by

.I size

and

.I attr

is too small.

.TP

.B EINVAL

.I size

is invalid; that is, it is smaller than the initial version of the

.I sched_attr

structure (48 bytes) or larger than the system page size.

.PP

In addition,

.BR sched_setattr ()

can fail for the following reasons:

.TP

.B E2BIG

The buffer specified by

.I size

and

.I attr

is larger than the kernel structure,

and one or more of the excess bytes is nonzero.

.TP

.B EBUSY

.B SCHED_DEADLINE

admission control failure, see

.BR sched (7).

.TP

.B EINVAL

.I attr.sched_policy

is not one of the recognized policies;

.I attr.sched_flags

contains a flag other than

.BR SCHED_FLAG_RESET_ON_FORK ;

or

.I attr.sched_priority

is invalid; or

.I attr.sched_policy

is

.BR SCHED_DEADLINE

and the deadline scheduling parameters in

.I attr

are invalid.

.TP

.B EPERM

The caller does not have appropriate privileges.

.TP

.B EPERM

The CPU affinity mask of the thread specified by

.I pid

does not include all CPUs in the system

(see

.BR sched_setaffinity (2)).

.SH VERSIONS

These system calls first appeared in Linux 3.14.

.\" FIXME . Add glibc version

.SH CONFORMING TO

These system calls are nonstandard Linux extensions.

.SH NOTES

.BR sched_setattr ()

provides a superset of the functionality of

.BR sched_setscheduler (2),

.BR sched_setparam (2),

.BR 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)

.BR setpriority (2).

Analogously,

.BR sched_getattr ()

provides a superset of the functionality of

.BR sched_getscheduler (2),

.BR sched_getparam (2),

and (partially)

.BR getpriority (2).

.SH BUGS

In Linux versions up to

.\" FIXME . patch sent to Peter Zijlstra

3.15,

.BR sched_settattr ()

failed with the error

.BR EFAULT

instead of

.BR E2BIG

for the case described in ERRORS.

.\" In Linux versions up to up 3.15,

.\" FIXME . patch from Peter Zijlstra pending

.\" .BR sched_setattr ()

.\" allowed a negative

.\" .I attr.sched_policy

.\" value.

.SH SEE ALSO

.ad l

.nh

.BR chrt (1),

.BR nice (2),

.BR sched_get_priority_max (2),

.BR sched_get_priority_min (2),

.BR sched_getaffinity (2),

.BR sched_getparam (2),

.BR sched_getscheduler (2),

.BR sched_rr_get_interval (2),

.BR sched_setaffinity (2),

.BR sched_setparam (2),

.BR sched_setscheduler (2),

.BR sched_yield (2),

.BR setpriority (2),

.BR pthread_getschedparam (3),

.BR pthread_setschedparam (3),

.BR pthread_setschedprio (3),

.BR capabilities (7),

.BR cpuset (7),

.BR sched (7)

.ad

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.