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Date: Tue, 13 May 2014 16:57:36 +0200
From: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: mtk.manpages@...il.com, Juri Lelli <juri.lelli@...il.com>,
Dario Faggioli <raistlin@...ux.it>,
lkml <linux-kernel@...r.kernel.org>,
"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>
Subject: [SCHED_DEADLINE man pages 1/2] sched_setattr.2
Hello Peter et al.
Here is the sched_attr.2 page as rendered text, with the
raw page source attached. Please carefully review.
Cheers,
Michael
NAME
sched_setattr, sched_getattr - set and get scheduling policy
and attributes
SYNOPSIS
#include <sched.h>
int sched_setattr(pid_t pid, const struct sched_attr *attr,
unsigned int flags);
int sched_getattr(pid_t pid, const 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 pol‐
icy 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 '0'. If the pro‐
vided 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 updates size 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 ker‐
nel 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 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 flags controlling scheduling behav‐
ior. Only one such flag is currently defined:
SCHED_FLAG_RESET_ON_FORK. As a result of including this
flag, children created by fork(2) do not inherit privi‐
leged scheduling policies. See sched(7) for details.
sched_nice
This field specifies the nice value to be set when spec‐
ifying sched_policy as SCHED_OTHER or SCHED_BATCH. The
nice value is a number in the range -20 (high priority)
to +19 (low priority); see setpriority(2).
sched_priority
This field specifies the static priority to be set when
specifying sched_policy as SCHED_FIFO or SCHED_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 dead‐
line 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 dead‐
line 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 speci‐
fied 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'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 fol‐
lowing reasons:
EINVAL attr is NULL; or pid is negative; or flags is not zero.
ESRCH The thread whose ID is pid could not be found.
In addition, sched_getattr() can fail for the following rea‐
sons:
E2BIG The buffer specified by size and attr 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 rea‐
sons:
E2BIG The buffer specified by size and attr 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 than
SCHED_FLAG_RESET_ON_FORK; or attr.sched_priority is
invalid; or attr.sched_policy is SCHED_DEADLINE and the
deadline scheduling parameters in attr are invalid.
EPERM The caller does not have appropriate privileges.
EPERM The caller's CPU affinity mask does not include all CPUs
in the system (see sched_setaffinity(2)).
VERSIONS
These system calls first appeared in Linux 3.14.
CONFORMING TO
These system calls are nonstandard Linux extensions.
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) set‐
priority(2). Analogously, sched_getattr() provides a superset
of the functionality of sched_getscheduler(2), sched_get‐
param(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
nice(2), sched_get_priority_max(2), sched_get_priority_min(2),
sched_getaffinity(2), sched_getscheduler(2), sched_getparam(2),
sched_rr_get_interval(2), sched_setaffinity(2),
sched_setscheduler(2), sched_setparam(2), sched_yield(2),
setpriority(2), pthread_getschedparam(3),
pthread_setschedparam(3), pthread_setschedprio(3),
capabilities(7), cpuset(7), sched(7)
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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