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Dd August 5, 2016
Dt SCHED 3
Os
Sh NAME
Nm sched_setparam ,
Nm sched_getparam ,
Nm sched_setscheduler ,
Nm sched_getscheduler ,
Nm sched_get_priority_max ,
Nm sched_get_priority_min ,
Nm sched_rr_get_interval ,
Nm sched_yield ,
Nm sched_protect ,
Nm sched_setaffinity_np ,
Nm sched_getaffinity_np
Nd process scheduling
Sh LIBRARY
Lb librt
Sh SYNOPSIS
In sched.h
Ft int
Fn sched_setparam "pid_t pid" "const struct sched_param *param"
Ft int
Fn sched_getparam "pid_t pid" "struct sched_param *param"
Ft int
Fn sched_setscheduler "pid_t pid" "int policy" "const struct sched_param *param"
Ft int
Fn sched_getscheduler "pid_t pid"
Ft int
Fn sched_get_priority_max "int policy"
Ft int
Fn sched_get_priority_min "int policy"
Ft int
Fn sched_rr_get_interval "pid_t pid" "struct timespec *interval"
Ft int
Fn sched_yield "void"
Ft int
Fn sched_setaffinity_np "pid_t pid" "size_t size" "cpuset_t *cpuset"
Ft int
Fn sched_getaffinity_np "pid_t pid" "size_t size" "cpuset_t *cpuset"
Ft int
Fn sched_protect "int priority"
Sh DESCRIPTION
This section describes the functions used to get scheduling information
about processes, and control the scheduling of processes.
Pp
Available scheduling policies (classes) are:
Bl -tag -width SCHED_OTHER
It Dv SCHED_OTHER
Time-sharing (TS) scheduling policy.
The default policy in
Nx .
It Dv SCHED_FIFO
First in, first out (FIFO) scheduling policy.
It Dv SCHED_RR
Round robin scheduling policy.
El
Pp
The
Fa struct sched_param
contains at least one member:
Bl -tag -width flags
It Fa sched_priority
Specifies the priority of the process.
For
Dv SCHED_OTHER ,
must be
Dv PRI_NONE ;
the kernel will dynamically assign priorities to the thread based on
CPU load.
El
Sh FUNCTIONS
Bl -tag -width compact
It Fn sched_setparam pid param
Sets the scheduling parameters for the process specified by
Fa pid
to
Fa param .
If the value of
Fa pid
is equal to zero, then the calling process is used.
It Fn sched_getparam pid param
Gets the scheduling parameters of the process specified by
Fa pid
into the structure
Fa param .
If the value of
Fa pid
is equal to zero, then the calling process is used.
It Fn sched_setscheduler pid policy param
Set the scheduling policy and parameters for the process specified by
Fa pid .
If the value of
Fa pid
is equal to zero, then the calling process is used.
It Fn sched_getscheduler pid
Returns the scheduling policy of the process specified by
Fa pid .
If the value of
Fa pid
is equal to zero, then the calling process is used.
It Fn sched_get_priority_max policy
Returns the maximal priority which may be used for the scheduling policy
specified by
Fa policy .
It Fn sched_get_priority_min policy
Returns the minimal priority which may be used for the scheduling policy
specified by
Fa policy .
It Fn sched_rr_get_interval pid interval
Returns the time quantum into the structure
Fa interval
of the process specified by
Fa pid .
If the value of
Fa pid
is equal to zero, then the calling process is used.
The process must be running at
Fa SCHED_RR
scheduling policy.
It Fn sched_yield
Yields a processor voluntarily and gives other threads a chance to run
without waiting for an involuntary preemptive switch.
It Fn sched_setaffinity_np pid size cpuset
Set the affinity mask specified by
Fa cpuset
for the process specified by
Fa pid .
At least one valid CPU must be set in the mask.
It Fn sched_getaffinity_np pid size cpuset
Get the affinity mask of the process specified by
Fa pid
into the
Fa cpuset .
It Fn sched_protect priority
Performs priority protection using the
Dv PTHREAD_PRIO_PROTECT
protocol.
This function will increase the protected priority of the caller thread to
Fa priority
if the current thread's protected priority is smaller than
Fa priority .
Multiple calls to
Fn sched_protect
with a positive priority will
Dq push
a priority level to the current thread, whereas calling
Fn sched_protect
with a
Fa priority
level of
Dv \-1
will
Dq pop
a priority level.
When the level reaches
Dv 0
(the same number of
Dq pushes
and
Dq pops
have been issued) the original thread priority will be restored.
El
Sh IMPLEMENTATION NOTES
Setting CPU
Xr affinity 3
requires super-user privileges.
Ordinary users can be allowed to control CPU affinity
of their threads via the
Pa security.models.extensions.user_set_cpu_affinity
Xr sysctl 7 .
See
Xr secmodel_extensions 9 .
Pp
Portable applications should not use the
Fn sched_setaffinity_np
and
Fn sched_getaffinity_np
functions.
Sh RETURN VALUES
Fn sched_protect ,
Fn sched_setparam ,
Fn sched_getparam ,
Fn sched_rr_get_interval ,
and
Fn sched_yield
return 0 on success.
Otherwise, \-1 is returned and
Va errno
is set to indicate the error.
Pp
Fn sched_setscheduler
returns the previously used scheduling policy on success.
Otherwise, \-1 is returned and
Va errno
is set to indicate the error.
Pp
Fn sched_getscheduler
returns the scheduling policy on success.
Otherwise, \-1 is returned and
Va errno
is set to indicate the error.
Pp
Fn sched_get_priority_max
and
Fn sched_get_priority_min
return the maximal/minimal priority value on success.
Otherwise, \-1 is returned and
Va errno
is set to indicate the error.
Pp
Fn sched_setaffinity_np
and
Fn sched_getaffinity_np
return 0 on success.
Otherwise, \-1 is returned and
Va errno
is set to indicate the error.
Sh ERRORS
The
Fn sched_setparam
and
Fn sched_setscheduler
functions fail if:
Bl -tag -width Er
It Bq Er EINVAL
At least one of the specified scheduling parameters was invalid.
It Bq Er EPERM
The calling process has no appropriate privileges to perform the operation.
It Bq Er ESRCH
No process can be found corresponding to the PID specified by
Fa pid ,
and the value of
Fa pid
is not zero.
El
Pp
The
Fn sched_getparam
and
Fn sched_getscheduler
functions fail if:
Bl -tag -width Er
It Bq Er EPERM
The calling process is not a super-user and its effective user id does not
match the effective user-id of the specified process.
It Bq Er ESRCH
No process can be found corresponding to that specified by
Fa pid ,
and the value of
Fa pid
is not zero.
El
Pp
The
Fn sched_get_priority_max
and
Fn sched_get_priority_min
functions fail if:
Bl -tag -width Er
It Bq Er EINVAL
The specified scheduling policy is invalid.
El
Pp
The
Fn sched_rr_get_interval
function fails if:
Bl -tag -width Er
It Bq Er ESRCH
No process can be found corresponding to that specified by
Fa pid ,
and the value of
Fa pid
is not zero.
El
Pp
The
Fn sched_protect
function fails if:
Bl -tag -width Er
It Bq Er EINVAL
The thread was not priority protected.
It Bq Er EPERM
The
Fa priority
parameter was out of range (not in the range between
Dv SCHED_PRIO_MIN
and
Dv SCHED_PRIO_MAX ) .
El
Sh SEE ALSO
Xr affinity 3 ,
Xr cpuset 3 ,
Xr pset 3 ,
Xr schedctl 8
Sh STANDARDS
These functions, except
Fn sched_setaffinity_np
and
Fn sched_getaffinity_np ,
are expected to conform the
St -p1003.1-2001
standard.
Sh HISTORY
The scheduling functions appeared in
Nx 5.0 .

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