Section (2) sched_setattr
Name
sched_setattr, sched_getattr — set and get scheduling policy and attributes
Synopsis
#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) ; |
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 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 _zsingle_quotesz_0_zsingle_quotesz_. 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 updatessize
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_zsingle_quotesz_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 aSIGXCPU
signal which is generated on each overrun.This
SIGXCPU
signal isprocess-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
asSCHED_OTHER
orSCHED_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
asSCHED_FIFO
orSCHED_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_zsingle_quotesz_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; orpid
is negative; orflags
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
andattr
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
andattr
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 thanSCHED_FLAG_RESET_ON_FORK
; orattr.sched_priority
is invalid; orattr.sched_policy
isSCHED_DEADLINE
and the deadline scheduling parameters inattr
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)).
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 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).
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_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)
COLOPHON
This page is part of release 5.04 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/.
Copyright (C) 2014 Michael Kerrisk <mtk.manpagesgmail.com> and Copyright (C) 2014 Peter Zijlstra <peterzinfradead.org> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |