1sched_setattr(2) System Calls Manual sched_setattr(2)
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6 sched_setattr, sched_getattr - set and get scheduling policy and at‐
7 tributes
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10 Standard C library (libc, -lc)
11
13 #include <sched.h> /* Definition of SCHED_* constants */
14 #include <sys/syscall.h> /* Definition of SYS_* constants */
15 #include <unistd.h>
16 int syscall(SYS_sched_setattr, pid_t pid, struct sched_attr *attr,
18 unsigned int flags);
19 int syscall(SYS_sched_getattr, pid_t pid, struct sched_attr *attr,
20 unsigned int size, unsigned int flags);
21 Note: glibc provides no wrappers for these system calls, necessitating
23 the use of syscall(2).
24
26 sched_setattr()
27 The sched_setattr() system call sets the scheduling policy and associ‐
28 ated attributes for the thread whose ID is specified in pid. If pid
29 equals zero, the scheduling policy and attributes of the calling thread
30 will be set.
31 Currently, Linux supports the following "normal" (i.e., non-real-time)
33 scheduling policies as values that may be specified in policy:
34 SCHED_OTHER the standard round-robin time-sharing policy;
36 SCHED_BATCH for "batch" style execution of processes; and
38 SCHED_IDLE for running very low priority background jobs.
40 Various "real-time" policies are also supported, for special time-crit‐
42 ical applications that need precise control over the way in which
43 runnable threads are selected for execution. For the rules governing
44 when a process may use these policies, see sched(7). The real-time
45 policies that may be specified in policy are:
46 SCHED_FIFO a first-in, first-out policy; and
48 SCHED_RR a round-robin policy.
50 Linux also provides the following policy:
52 SCHED_DEADLINE
54 a deadline scheduling policy; see sched(7) for details.
55 The attr argument is a pointer to a structure that defines the new
57 scheduling policy and attributes for the specified thread. This struc‐
58 ture has the following form:
59 struct sched_attr {
61 u32 size; /* Size of this structure */
62 u32 sched_policy; /* Policy (SCHED_*) */
63 u64 sched_flags; /* Flags */
64 s32 sched_nice; /* Nice value (SCHED_OTHER,
65 SCHED_BATCH) */
66 u32 sched_priority; /* Static priority (SCHED_FIFO,
67 SCHED_RR) */
68 /* Remaining fields are for SCHED_DEADLINE */
69 u64 sched_runtime;
70 u64 sched_deadline;
71 u64 sched_period;
72 };
73 The fields of the sched_attr structure are as follows:
75 size This field should be set to the size of the structure in bytes,
77 as in sizeof(struct sched_attr). If the provided structure is
78 smaller than the kernel structure, any additional fields are as‐
79 sumed to be '0'. If the provided structure is larger than the
80 kernel structure, the kernel verifies that all additional fields
81 are 0; if they are not, sched_setattr() fails with the error
82 E2BIG and updates size to contain the size of the kernel struc‐
83 ture.
84 The above behavior when the size of the user-space sched_attr
86 structure does not match the size of the kernel structure allows
87 for future extensibility of the interface. Malformed applica‐
88 tions that pass oversize structures won't break in the future if
89 the size of the kernel sched_attr structure is increased. In
90 the future, it could also allow applications that know about a
91 larger user-space sched_attr structure to determine whether they
92 are running on an older kernel that does not support the larger
93 structure.
94 sched_policy
96 This field specifies the scheduling policy, as one of the
97 SCHED_* values listed above.
98 sched_flags
100 This field contains zero or more of the following flags that are
101 ORed together to control scheduling behavior:
102 SCHED_FLAG_RESET_ON_FORK
104 Children created by fork(2) do not inherit privileged
105 scheduling policies. See sched(7) for details.
106 SCHED_FLAG_RECLAIM (since Linux 4.13)
108 This flag allows a SCHED_DEADLINE thread to reclaim band‐
109 width unused by other real-time threads.
110 SCHED_FLAG_DL_OVERRUN (since Linux 4.16)
112 This flag allows an application to get informed about
113 run-time overruns in SCHED_DEADLINE threads. Such over‐
114 runs may be caused by (for example) coarse execution time
115 accounting or incorrect parameter assignment. Notifica‐
116 tion takes the form of a SIGXCPU signal which is gener‐
117 ated on each overrun.
118 This SIGXCPU signal is process-directed (see signal(7))
120 rather than thread-directed. This is probably a bug. On
121 the one hand, sched_setattr() is being used to set a per-
122 thread attribute. On the other hand, if the process-di‐
123 rected signal is delivered to a thread inside the process
124 other than the one that had a run-time overrun, the ap‐
125 plication has no way of knowing which thread overran.
126 sched_nice
128 This field specifies the nice value to be set when specifying
129 sched_policy as SCHED_OTHER or SCHED_BATCH. The nice value is a
130 number in the range -20 (high priority) to +19 (low priority);
131 see sched(7).
132 sched_priority
134 This field specifies the static priority to be set when specify‐
135 ing sched_policy as SCHED_FIFO or SCHED_RR. The allowed range
136 of priorities for these policies can be determined using
137 sched_get_priority_min(2) and sched_get_priority_max(2). For
138 other policies, this field must be specified as 0.
139 sched_runtime
141 This field specifies the "Runtime" parameter for deadline sched‐
142 uling. The value is expressed in nanoseconds. This field, and
143 the next two fields, are used only for SCHED_DEADLINE schedul‐
144 ing; for further details, see sched(7).
145 sched_deadline
147 This field specifies the "Deadline" parameter for deadline
148 scheduling. The value is expressed in nanoseconds.
149 sched_period
151 This field specifies the "Period" parameter for deadline sched‐
152 uling. The value is expressed in nanoseconds.
153 The flags argument is provided to allow for future extensions to the
155 interface; in the current implementation it must be specified as 0.
156 sched_getattr()
158 The sched_getattr() system call fetches the scheduling policy and the
159 associated attributes for the thread whose ID is specified in pid. If
160 pid equals zero, the scheduling policy and attributes of the calling
161 thread will be retrieved.
162 The size argument should be set to the size of the sched_attr structure
164 as known to user space. The value must be at least as large as the
165 size of the initially published sched_attr structure, or the call fails
166 with the error EINVAL.
167 The retrieved scheduling attributes are placed in the fields of the
169 sched_attr structure pointed to by attr. The kernel sets attr.size to
170 the size of its sched_attr structure.
171 If the caller-provided attr buffer is larger than the kernel's
173 sched_attr structure, the additional bytes in the user-space structure
174 are not touched. If the caller-provided structure is smaller than the
175 kernel sched_attr structure, the kernel will silently not return any
176 values which would be stored outside the provided space. As with
177 sched_setattr(), these semantics allow for future extensibility of the
178 interface.
179 The flags argument is provided to allow for future extensions to the
181 interface; in the current implementation it must be specified as 0.
182
184 On success, sched_setattr() and sched_getattr() return 0. On error, -1
185 is returned, and errno is set to indicate the error.
186
188 sched_getattr() and sched_setattr() can both fail for the following
189 reasons:
190 EINVAL attr is NULL; or pid is negative; or flags is not zero.
192 ESRCH The thread whose ID is pid could not be found.
194 In addition, sched_getattr() can fail for the following reasons:
196 E2BIG The buffer specified by size and attr is too small.
198 EINVAL size is invalid; that is, it is smaller than the initial version
200 of the sched_attr structure (48 bytes) or larger than the system
201 page size.
202 In addition, sched_setattr() can fail for the following reasons:
204 E2BIG The buffer specified by size and attr is larger than the kernel
206 structure, and one or more of the excess bytes is nonzero.
207 EBUSY SCHED_DEADLINE admission control failure, see sched(7).
209 EINVAL attr.sched_policy is not one of the recognized policies;
211 attr.sched_flags contains a flag other than SCHED_FLAG_RE‐
212 SET_ON_FORK; or attr.sched_priority is invalid; or
213 attr.sched_policy is SCHED_DEADLINE and the deadline scheduling
214 parameters in attr are invalid.
215 EPERM The caller does not have appropriate privileges.
217 EPERM The CPU affinity mask of the thread specified by pid does not
219 include all CPUs in the system (see sched_setaffinity(2)).
220
222 Linux.
223
225 Linux 3.14.
226
228 glibc does not provide wrappers for these system calls; call them using
229 syscall(2).
230 sched_setattr() provides a superset of the functionality of
232 sched_setscheduler(2), sched_setparam(2), nice(2), and (other than the
233 ability to set the priority of all processes belonging to a specified
234 user or all processes in a specified group) setpriority(2). Analo‐
235 gously, sched_getattr() provides a superset of the functionality of
236 sched_getscheduler(2), sched_getparam(2), and (partially) getprior‐
237 ity(2).
238
240 In Linux versions up to 3.15, sched_setattr() failed with the error
241 EFAULT instead of E2BIG for the case described in ERRORS.
242 Up to Linux 5.3, sched_getattr() failed with the error EFBIG if the in-
244 kernel sched_attr structure was larger than the size passed by user
245 space.
246
248 chrt(1), nice(2), sched_get_priority_max(2), sched_get_priority_min(2),
249 sched_getaffinity(2), sched_getparam(2), sched_getscheduler(2),
250 sched_rr_get_interval(2), sched_setaffinity(2), sched_setparam(2),
251 sched_setscheduler(2), sched_yield(2), setpriority(2),
252 pthread_getschedparam(3), pthread_setschedparam(3),
253 pthread_setschedprio(3), capabilities(7), cpuset(7), sched(7)
254Linux man-pages 6.05 2023-03-30 sched_setattr(2)