man2/sched_setattr.2

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   2 .\" and Copyright (C) 2014 Peter Zijlstra <peterz@infradead.org>
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  26 .TH SCHED_SETATTR 2 2017-09-15 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 sched_setattr, sched_getattr \-
  29 set and get scheduling policy and attributes
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <sched.h>
  33 .PP
  34 .BI "int sched_setattr(pid_t " pid ", struct sched_attr *" attr ,
  35 .BI "                  unsigned int " flags );
  36 .PP
  37 .BI "int sched_getattr(pid_t " pid ", struct sched_attr *" attr ,
  38 .BI "                  unsigned int " size ", unsigned int " flags );
  39 .fi
  40 .\" FIXME . Add feature test macro requirements
  41 .SH DESCRIPTION
  42 .SS sched_setattr()
  43 The
  44 .BR sched_setattr ()
  45 system call sets the scheduling policy and
  46 associated attributes for the thread whose ID is specified in
  47 .IR pid .
  48 If
  49 .I pid
  50 equals zero,
  51 the scheduling policy and attributes of the calling thread will be set.
  52 .PP
  53 Currently, Linux supports the following "normal"
  54 (i.e., non-real-time) scheduling policies as values that may be specified in
  55 .IR policy :
  56 .TP 14
  57 .BR SCHED_OTHER
  58 the standard round-robin time-sharing policy;
  59 .\" In the 2.6 kernel sources, SCHED_OTHER is actually called
  60 .\" SCHED_NORMAL.
  61 .TP
  62 .BR SCHED_BATCH
  63 for "batch" style execution of processes; and
  64 .TP
  65 .BR SCHED_IDLE
  66 for running
  67 .I very
  68 low priority background jobs.
  69 .PP
  70 Various "real-time" policies are also supported,
  71 for special time-critical applications that need precise control over
  72 the way in which runnable threads are selected for execution.
  73 For the rules governing when a process may use these policies, see
  74 .BR sched (7).
  75 The real-time policies that may be specified in
  76 .IR policy
  77 are:
  78 .TP 14
  79 .BR SCHED_FIFO
  80 a first-in, first-out policy; and
  81 .TP
  82 .BR SCHED_RR
  83 a round-robin policy.
  84 .PP
  85 Linux also provides the following policy:
  86 .TP 14
  87 .B SCHED_DEADLINE
  88 a deadline scheduling policy; see
  89 .BR sched (7)
  90 for details.
  91 .PP
  92 The
  93 .I attr
  94 argument is a pointer to a structure that defines
  95 the new scheduling policy and attributes for the specified thread.
  96 This structure has the following form:
  97 .PP
  98 .in +4n
  99 .EX
 100 struct sched_attr {
 101     u32 size;              /* Size of this structure */
 102     u32 sched_policy;      /* Policy (SCHED_*) */
 103     u64 sched_flags;       /* Flags */
 104     s32 sched_nice;        /* Nice value (SCHED_OTHER,
 105                               SCHED_BATCH) */
 106     u32 sched_priority;    /* Static priority (SCHED_FIFO,
 107                               SCHED_RR) */
 108     /* Remaining fields are for SCHED_DEADLINE */
 109     u64 sched_runtime;
 110     u64 sched_deadline;
 111     u64 sched_period;
 112 };
 113 .EE
 114 .in
 115 .PP
 116 The fields of this structure are as follows:
 117 .TP
 118 .B size
 119 This field should be set to the size of the structure in bytes, as in
 120 .IR "sizeof(struct sched_attr)" .
 121 If the provided structure is smaller than the kernel structure,
 122 any additional fields are assumed to be '0'.
 123 If the provided structure is larger than the kernel structure,
 124 the kernel verifies that all additional fields are 0;
 125 if they are not,
 126 .BR sched_setattr ()
 127 fails with the error
 128 .BR E2BIG
 129 and updates
 130 .I size
 131 to contain the size of the kernel structure.
 132 .IP
 133 The above behavior when the size of the user-space
 134 .I sched_attr
 135 structure does not match the size of the kernel structure
 136 allows for future extensibility of the interface.
 137 Malformed applications that pass oversize structures
 138 won't break in the future if the size of the kernel
 139 .I sched_attr
 140 structure is increased.
 141 In the future,
 142 it could also allow applications that know about a larger user-space
 143 .I sched_attr
 144 structure to determine whether they are running on an older kernel
 145 that does not support the larger structure.
 146 .TP
 147 .I sched_policy
 148 This field specifies the scheduling policy, as one of the
 149 .BR SCHED_*
 150 values listed above.
 151 .TP
 152 .I sched_flags
 153 This field contains contains zero or more of the following flags
 154 that are ORed together to control scheduling behavior:
 155 .RS
 156 .TP
 157 .BR SCHED_FLAG_RESET_ON_FORK
 158 Children created by
 159 .BR fork (2)
 160 do not inherit privileged scheduling policies.
 161 See
 162 .BR sched (7)
 163 for details.
 164 .TP
 165 .BR SCHED_FLAG_RECLAIM " (since Linux 4.13)"
 166 .\" 2d4283e9d583a3ee8cfb1cbb9c1270614df4c29d
 167 This flag allows a
 168 .BR SCHED_DEADLINE
 169 task to reclaim bandwidth unused by other real-time tasks through the GRUB
 170 algorithm.
 171 .TP
 172 .BR SCHED_FLAG_DL_OVERRUN " (since Linux 4.16)"
 173 .\" commit 34be39305a77b8b1ec9f279163c7cdb6cc719b91
 174 This flag allows a
 175 .BR SCHED_DEADLINE
 176 task to get informed about run-time overruns through the delivery of
 177 .B SIGXCPU
 178 signals.
 179 .RE
 180 .TP
 181 .I sched_nice
 182 This field specifies the nice value to be set when specifying
 183 .IR sched_policy
 184 as
 185 .BR SCHED_OTHER
 186 or
 187 .BR SCHED_BATCH .
 188 The nice value is a number in the range \-20 (high priority)
 189 to +19 (low priority); see
 190 .BR sched (7).
 191 .TP
 192 .I sched_priority
 193 This field specifies the static priority to be set when specifying
 194 .IR sched_policy
 195 as
 196 .BR SCHED_FIFO
 197 or
 198 .BR SCHED_RR .
 199 The allowed range of priorities for these policies can be determined using
 200 .BR sched_get_priority_min (2)
 201 and
 202 .BR sched_get_priority_max (2).
 203 For other policies, this field must be specified as 0.
 204 .TP
 205 .I sched_runtime
 206 This field specifies the "Runtime" parameter for deadline scheduling.
 207 The value is expressed in nanoseconds.
 208 This field, and the next two fields,
 209 are used only for
 210 .BR SCHED_DEADLINE
 211 scheduling; for further details, see
 212 .BR sched (7).
 213 .TP
 214 .I sched_deadline
 215 This field specifies the "Deadline" parameter for deadline scheduling.
 216 The value is expressed in nanoseconds.
 217 .TP
 218 .I sched_period
 219 This field specifies the "Period" parameter for deadline scheduling.
 220 The value is expressed in nanoseconds.
 221 .PP
 222 The
 223 .I flags
 224 argument is provided to allow for future extensions to the interface;
 225 in the current implementation it must be specified as 0.
 226 .\"
 227 .\"
 228 .SS sched_getattr()
 229 The
 230 .BR sched_getattr ()
 231 system call fetches the scheduling policy and the
 232 associated attributes for the thread whose ID is specified in
 233 .IR pid .
 234 If
 235 .I pid
 236 equals zero,
 237 the scheduling policy and attributes of the calling thread
 238 will be retrieved.
 239 .PP
 240 The
 241 .I size
 242 argument should be set to the size of the
 243 .I sched_attr
 244 structure as known to user space.
 245 The value must be at least as large as the size of the initially published
 246 .I sched_attr
 247 structure, or the call fails with the error
 248 .BR EINVAL .
 249 .PP
 250 The retrieved scheduling attributes are placed in the fields of the
 251 .I sched_attr
 252 structure pointed to by
 253 .IR attr .
 254 The kernel sets
 255 .I attr.size
 256 to the size of its
 257 .I sched_attr
 258 structure.
 259 .PP
 260 If the caller-provided
 261 .I attr
 262 buffer is larger than the kernel's
 263 .I sched_attr
 264 structure,
 265 the additional bytes in the user-space structure are not touched.
 266 If the caller-provided structure is smaller than the kernel
 267 .I sched_attr
 268 structure and the kernel needs to return values outside the provided space,
 269 .BR sched_getattr ()
 270 fails with the error
 271 .BR E2BIG .
 272 As with
 273 .BR sched_setattr (),
 274 these semantics allow for future extensibility of the interface.
 275 .PP
 276 The
 277 .I flags
 278 argument is provided to allow for future extensions to the interface;
 279 in the current implementation it must be specified as 0.
 280 .SH RETURN VALUE
 281 On success,
 282 .BR sched_setattr ()
 283 and
 284 .BR sched_getattr ()
 285 return 0.
 286 On error, \-1 is returned, and
 287 .I errno
 288 is set to indicate the cause of the error.
 289 .SH ERRORS
 290 .BR sched_getattr ()
 291 and
 292 .BR sched_setattr ()
 293 can both fail for the following reasons:
 294 .TP
 295 .B EINVAL
 296 .I attr
 297 is NULL; or
 298 .I pid
 299 is negative; or
 300 .I flags
 301 is not zero.
 302 .TP
 303 .B ESRCH
 304 The thread whose ID is
 305 .I pid
 306 could not be found.
 307 .PP
 308 In addition,
 309 .BR sched_getattr ()
 310 can fail for the following reasons:
 311 .TP
 312 .B E2BIG
 313 The buffer specified by
 314 .I size
 315 and
 316 .I attr
 317 is too small.
 318 .TP
 319 .B EINVAL
 320 .I size
 321 is invalid; that is, it is smaller than the initial version of the
 322 .I sched_attr
 323 structure (48 bytes) or larger than the system page size.
 324 .PP
 325 In addition,
 326 .BR sched_setattr ()
 327 can fail for the following reasons:
 328 .TP
 329 .B E2BIG
 330 The buffer specified by
 331 .I size
 332 and
 333 .I attr
 334 is larger than the kernel structure,
 335 and one or more of the excess bytes is nonzero.
 336 .TP
 337 .B EBUSY
 338 .B SCHED_DEADLINE
 339 admission control failure, see
 340 .BR sched (7).
 341 .TP
 342 .B EINVAL
 343 .I attr.sched_policy
 344 is not one of the recognized policies;
 345 .I attr.sched_flags
 346 contains a flag other than
 347 .BR SCHED_FLAG_RESET_ON_FORK ;
 348 or
 349 .I attr.sched_priority
 350 is invalid; or
 351 .I attr.sched_policy
 352 is
 353 .BR SCHED_DEADLINE
 354 and the deadline scheduling parameters in
 355 .I attr
 356 are invalid.
 357 .TP
 358 .B EPERM
 359 The caller does not have appropriate privileges.
 360 .TP
 361 .B EPERM
 362 The CPU affinity mask of the thread specified by
 363 .I pid
 364 does not include all CPUs in the system
 365 (see
 366 .BR sched_setaffinity (2)).
 367 .SH VERSIONS
 368 These system calls first appeared in Linux 3.14.
 369 .\" FIXME . Add glibc version
 370 .SH CONFORMING TO
 371 These system calls are nonstandard Linux extensions.
 372 .SH NOTES
 373 .BR sched_setattr ()
 374 provides a superset of the functionality of
 375 .BR sched_setscheduler (2),
 376 .BR sched_setparam (2),
 377 .BR nice (2),
 378 and (other than the ability to set the priority of all processes
 379 belonging to a specified user or all processes in a specified group)
 380 .BR setpriority (2).
 381 Analogously,
 382 .BR sched_getattr ()
 383 provides a superset of the functionality of
 384 .BR sched_getscheduler (2),
 385 .BR sched_getparam (2),
 386 and (partially)
 387 .BR getpriority (2).
 388 .SH BUGS
 389 In Linux versions up to
 390 .\" FIXME . patch sent to Peter Zijlstra
 391 3.15,
 392 .BR sched_settattr ()
 393 failed with the error
 394 .BR EFAULT
 395 instead of
 396 .BR E2BIG
 397 for the case described in ERRORS.
 398 .\" In Linux versions up to up 3.15,
 399 .\" FIXME . patch from Peter Zijlstra pending
 400 .\" .BR sched_setattr ()
 401 .\" allowed a negative
 402 .\" .I attr.sched_policy
 403 .\" value.
 404 .SH SEE ALSO
 405 .ad l
 406 .nh
 407 .BR chrt (1),
 408 .BR nice (2),
 409 .BR sched_get_priority_max (2),
 410 .BR sched_get_priority_min (2),
 411 .BR sched_getaffinity (2),
 412 .BR sched_getparam (2),
 413 .BR sched_getscheduler (2),
 414 .BR sched_rr_get_interval (2),
 415 .BR sched_setaffinity (2),
 416 .BR sched_setparam (2),
 417 .BR sched_setscheduler (2),
 418 .BR sched_yield (2),
 419 .BR setpriority (2),
 420 .BR pthread_getschedparam (3),
 421 .BR pthread_setschedparam (3),
 422 .BR pthread_setschedprio (3),
 423 .BR capabilities (7),
 424 .BR cpuset (7),
 425 .BR sched (7)
 426 .ad