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27 .Dd March 12, 1998
28 .Dt SCHED_SETPARAM 2
29 .Os
30 .Sh NAME
31 .Nm sched_setparam ,
32 .Nm sched_getparam
33 .Nd set/get scheduling parameters
34 .Sh LIBRARY
35 .Lb libc
36 .Sh SYNOPSIS
37 .In sched.h
38 .Ft int
39 .Fn sched_setparam "pid_t pid" "const struct sched_param *param"
40 .Ft int
41 .Fn sched_getparam "pid_t pid" "struct sched_param *param"
42 .Sh DESCRIPTION
43 The
44 .Fn sched_setparam
45 function sets the scheduling parameters of the process specified by
46 .Fa pid
47 to the values specified by the
48 .Fa sched_param
49 structure pointed to by
50 .Fa param .
51 The value of the
52 .Fa sched_priority
53 member in the
54 .Fa param
55 structure must be any integer within the inclusive priority range for
56 the current scheduling policy of the process specified by
57 .Fa pid .
58 Higher numerical values for the priority represent higher priorities.
59 .Pp
60 In this implementation, if the value of
61 .Fa pid
62 is negative the function will fail.
63 .Pp
64 If a process specified by
65 .Fa pid
66 exists and if the calling process has permission, the scheduling
67 parameters are set for the process whose process ID is equal to
68 .Fa pid .
69 .Pp
70 If
71 .Fa pid
72 is zero, the scheduling parameters are set for the calling process.
73 .Pp
74 In this implementation, the policy of when a process can affect
75 the scheduling parameters of another process is specified in
76 .St -p1003.1b-93
77 as a write-style operation.
78 .Pp
79 The target process, whether it is running or not running, will resume
80 execution after all other runnable processes of equal or greater
81 priority have been scheduled to run.
82 .Pp
83 If the priority of the process specified by the
84 .Fa pid
85 argument is set higher than that of the lowest priority running process
86 and if the specified process is ready to run, the process specified by
87 the
88 .Fa pid
89 argument will preempt a lowest priority running process. Similarly, if
90 the process calling
91 .Fn sched_setparam
92 sets its own priority lower than that of one or more other nonempty
93 process lists, then the process that is the head of the highest priority
94 list will also preempt the calling process. Thus, in either case, the
95 originating process might not receive notification of the completion of
96 the requested priority change until the higher priority process has
97 executed.
98 .Pp
99 In this implementation, when the current scheduling policy for the
100 process specified by
101 .Fa pid
102 is normal timesharing (SCHED_OTHER, aka SCHED_NORMAL when not POSIX-source)
103 or the idle policy (SCHED_IDLE when not POSIX-source) then the behavior
104 is as if the process had been running under SCHED_RR with a priority
105 lower than any actual realtime priority.
106 .Pp
107 The
108 .Fn sched_getparam
109 function will return the scheduling parameters of a process specified
110 by
111 .Fa pid
112 in the
113 .Fa sched_param
114 structure pointed to by
115 .Fa param .
116 .Pp
117 If a process specified by
118 .Fa pid
119 exists and if the calling process has permission,
120 the scheduling parameters for the process whose process ID is equal to
121 .Fa pid
122 are returned.
123 .Pp
124 In this implementation, the policy of when a process can obtain the
125 scheduling parameters of another process are detailed in
126 .St -p1003.1b-93
127 as a read-style operation.
128 .Pp
129 If
130 .Fa pid
131 is zero, the scheduling parameters for the calling process will be
132 returned. In this implementation, the
133 .Fa sched_getparam
134 function will fail if
135 .Fa pid
136 is negative.
137 .Sh RETURN VALUES
138 .Rv -std
139 .Sh ERRORS
140 On failure
141 .Va errno
142 will be set to the corresponding value:
143 .Bl -tag -width Er
144 .It Bq Er ENOSYS
145 The system is not configured to support this functionality.
146 .It Bq Er EPERM
147 The requesting process doesn not have permission as detailed in
148 .St -p1003.1b-93 .
149 .It Bq Er ESRCH
150 No process can be found corresponding to that specified by
151 .Fa pid .
152 .It Bq Er EINVAL
153 For
154 .Fn sched_setparam :
155 one or more of the requested scheduling parameters
156 is outside the range defined for the scheduling policy of the specified
157 .Fa pid .
158 .El
159 .Sh SEE ALSO
160 .Xr sched_getscheduler 2 ,
161 .Xr sched_get_priority_max 2 ,
162 .Xr sched_get_priority_min 2 ,
163 .Xr sched_rr_get_interval 2 ,
164 .Xr sched_setscheduler 2 ,
165 .Xr sched_yield 2
166 .Sh STANDARDS
167 The
168 .Fn sched_setparam
169 and
170 .Fn sched_getparam
171 functions conform to
172 .St -p1003.1b-93 .