1SCHED_SETATTR(2) Linux Programmer's Manual SCHED_SETATTR(2)
2
6 sched_setattr, sched_getattr - set and get scheduling policy and
7 attributes
8
10 #include <sched.h>
11 int sched_setattr(pid_t pid, struct sched_attr *attr,
13 unsigned int flags);
14 int sched_getattr(pid_t pid, struct sched_attr *attr,
16 unsigned int size, unsigned int flags);
17
19 sched_setattr()
20 The sched_setattr() system call sets the scheduling policy and associ‐
21 ated attributes for the thread whose ID is specified in pid. If pid
22 equals zero, the scheduling policy and attributes of the calling thread
23 will be set.
24 Currently, Linux supports the following "normal" (i.e., non-real-time)
26 scheduling policies as values that may be specified in policy:
27 SCHED_OTHER the standard round-robin time-sharing policy;
29 SCHED_BATCH for "batch" style execution of processes; and
31 SCHED_IDLE for running very low priority background jobs.
33 Various "real-time" policies are also supported, for special time-crit‐
35 ical applications that need precise control over the way in which
36 runnable threads are selected for execution. For the rules governing
37 when a process may use these policies, see sched(7). The real-time
38 policies that may be specified in policy are:
39 SCHED_FIFO a first-in, first-out policy; and
41 SCHED_RR a round-robin policy.
43 Linux also provides the following policy:
45 SCHED_DEADLINE
47 a deadline scheduling policy; see sched(7) for details.
48 The attr argument is a pointer to a structure that defines the new
50 scheduling policy and attributes for the specified thread. This struc‐
51 ture has the following form:
52 struct sched_attr {
54 u32 size; /* Size of this structure */
55 u32 sched_policy; /* Policy (SCHED_*) */
56 u64 sched_flags; /* Flags */
57 s32 sched_nice; /* Nice value (SCHED_OTHER,
58 SCHED_BATCH) */
59 u32 sched_priority; /* Static priority (SCHED_FIFO,
60 SCHED_RR) */
61 /* Remaining fields are for SCHED_DEADLINE */
62 u64 sched_runtime;
63 u64 sched_deadline;
64 u64 sched_period;
65 };
66 The fields of this structure are as follows:
68 size This field should be set to the size of the structure in bytes,
70 as in sizeof(struct sched_attr). If the provided structure is
71 smaller than the kernel structure, any additional fields are
72 assumed to be '0'. If the provided structure is larger than the
73 kernel structure, the kernel verifies that all additional fields
74 are 0; if they are not, sched_setattr() fails with the error
75 E2BIG and updates size to contain the size of the kernel struc‐
76 ture.
77 The above behavior when the size of the user-space sched_attr
79 structure does not match the size of the kernel structure allows
80 for future extensibility of the interface. Malformed applica‐
81 tions that pass oversize structures won't break in the future if
82 the size of the kernel sched_attr structure is increased. In
83 the future, it could also allow applications that know about a
84 larger user-space sched_attr structure to determine whether they
85 are running on an older kernel that does not support the larger
86 structure.
87 sched_policy
89 This field specifies the scheduling policy, as one of the
90 SCHED_* values listed above.
91 sched_flags
93 This field contains flags controlling scheduling behavior. Only
94 one such flag is currently defined: SCHED_FLAG_RESET_ON_FORK.
95 As a result of including this flag, children created by fork(2)
96 do not inherit privileged scheduling policies. See sched(7) for
97 details.
98 sched_nice
100 This field specifies the nice value to be set when specifying
101 sched_policy as SCHED_OTHER or SCHED_BATCH. The nice value is a
102 number in the range -20 (high priority) to +19 (low priority);
103 see sched(7).
104 sched_priority
106 This field specifies the static priority to be set when specify‐
107 ing sched_policy as SCHED_FIFO or SCHED_RR. The allowed range
108 of priorities for these policies can be determined using
109 sched_get_priority_min(2) and sched_get_priority_max(2). For
110 other policies, this field must be specified as 0.
111 sched_runtime
113 This field specifies the "Runtime" parameter for deadline sched‐
114 uling. The value is expressed in nanoseconds. This field, and
115 the next two fields, are used only for SCHED_DEADLINE schedul‐
116 ing; for further details, see sched(7).
117 sched_deadline
119 This field specifies the "Deadline" parameter for deadline
120 scheduling. The value is expressed in nanoseconds.
121 sched_period
123 This field specifies the "Period" parameter for deadline sched‐
124 uling. The value is expressed in nanoseconds.
125 The flags argument is provided to allow for future extensions to the
127 interface; in the current implementation it must be specified as 0.
128 sched_getattr()
130 The sched_getattr() system call fetches the scheduling policy and the
131 associated attributes for the thread whose ID is specified in pid. If
132 pid equals zero, the scheduling policy and attributes of the calling
133 thread will be retrieved.
134 The size argument should be set to the size of the sched_attr structure
136 as known to user space. The value must be at least as large as the
137 size of the initially published sched_attr structure, or the call fails
138 with the error EINVAL.
139 The retrieved scheduling attributes are placed in the fields of the
141 sched_attr structure pointed to by attr. The kernel sets attr.size to
142 the size of its sched_attr structure.
143 If the caller-provided attr buffer is larger than the kernel's
145 sched_attr structure, the additional bytes in the user-space structure
146 are not touched. If the caller-provided structure is smaller than the
147 kernel sched_attr structure and the kernel needs to return values out‐
148 side the provided space, sched_getattr() fails with the error E2BIG.
149 As with sched_setattr(), these semantics allow for future extensibility
150 of the interface.
151 The flags argument is provided to allow for future extensions to the
153 interface; in the current implementation it must be specified as 0.
154
156 On success, sched_setattr() and sched_getattr() return 0. On error, -1
157 is returned, and errno is set to indicate the cause of the error.
158
160 sched_getattr() and sched_setattr() can both fail for the following
161 reasons:
162 EINVAL attr is NULL; or pid is negative; or flags is not zero.
164 ESRCH The thread whose ID is pid could not be found.
166 In addition, sched_getattr() can fail for the following reasons:
168 E2BIG The buffer specified by size and attr is too small.
170 EINVAL size is invalid; that is, it is smaller than the initial version
172 of the sched_attr structure (48 bytes) or larger than the system
173 page size.
174 In addition, sched_setattr() can fail for the following reasons:
176 E2BIG The buffer specified by size and attr is larger than the kernel
178 structure, and one or more of the excess bytes is nonzero.
179 EBUSY SCHED_DEADLINE admission control failure, see sched(7).
181 EINVAL attr.sched_policy is not one of the recognized policies;
183 attr.sched_flags contains a flag other than
184 SCHED_FLAG_RESET_ON_FORK; or attr.sched_priority is invalid; or
185 attr.sched_policy is SCHED_DEADLINE and the deadline scheduling
186 parameters in attr are invalid.
187 EPERM The caller does not have appropriate privileges.
189 EPERM The CPU affinity mask of the thread specified by pid does not
191 include all CPUs in the system (see sched_setaffinity(2)).
192
194 These system calls first appeared in Linux 3.14.
195
197 These system calls are nonstandard Linux extensions.
198
200 sched_setattr() provides a superset of the functionality of
201 sched_setscheduler(2), sched_setparam(2), nice(2), and (other than the
202 ability to set the priority of all processes belonging to a specified
203 user or all processes in a specified group) setpriority(2). Analo‐
204 gously, sched_getattr() provides a superset of the functionality of
205 sched_getscheduler(2), sched_getparam(2), and (partially) getprior‐
206 ity(2).
207
209 In Linux versions up to 3.15, sched_settattr() failed with the error
210 EFAULT instead of E2BIG for the case described in ERRORS.
211
213 chrt(1), nice(2), sched_get_priority_max(2), sched_get_priority_min(2),
214 sched_getaffinity(2), sched_getparam(2), sched_getscheduler(2),
215 sched_rr_get_interval(2), sched_setaffinity(2), sched_setparam(2),
216 sched_setscheduler(2), sched_yield(2), setpriority(2),
217 pthread_getschedparam(3), pthread_setschedparam(3),
218 pthread_setschedprio(3), capabilities(7), cpuset(7), sched(7)
219
221 This page is part of release 4.15 of the Linux man-pages project. A
222 description of the project, information about reporting bugs, and the
223 latest version of this page, can be found at
224 https://www.kernel.org/doc/man-pages/.
225Linux 2017-09-15 SCHED_SETATTR(2)