1 | @c |
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2 | @c COPYRIGHT (c) 1988-1998. |
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3 | @c On-Line Applications Research Corporation (OAR). |
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4 | @c All rights reserved. |
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5 | @c |
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6 | @c $Id$ |
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7 | @c |
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8 | |
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9 | @chapter Scheduler Manager |
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10 | |
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11 | @section Introduction |
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12 | |
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13 | The scheduler manager ... |
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14 | |
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15 | The directives provided by the scheduler manager are: |
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16 | |
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17 | @itemize @bullet |
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18 | @item @code{sched_get_priority_min} - |
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19 | @item @code{sched_get_priority_max} - |
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20 | @item @code{sched_rr_get_interval} - |
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21 | @item @code{sched_yield} - |
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22 | @end itemize |
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23 | |
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24 | @section Background |
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25 | |
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26 | @subsection Priority |
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27 | |
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28 | In the RTEMS implementation of the POSIX API, the priorities range from |
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29 | the low priority of sched_get_priority_min() to the highest priority of |
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30 | sched_get_priority_max(). Numerically higher values represent higher |
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31 | priorities. |
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32 | |
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33 | @subsection Scheduling Policies |
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34 | |
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35 | The following scheduling policies are available: |
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36 | |
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37 | @table @b |
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38 | @item SCHED_FIFO |
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39 | Priority-based, preemptive scheduling with no timeslicing. This is equivalent |
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40 | to what is called "manual round-robin" scheduling. |
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41 | |
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42 | @item SCHED_RR |
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43 | Priority-based, preemptive scheduling with timeslicing. Time quantums are |
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44 | maintained on a per-thread basis and are not reset at each context switch. |
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45 | Thus, a thread which is preempted and subsequently resumes execution will |
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46 | attempt to complete the unused portion of its time quantum. |
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47 | |
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48 | @item SCHED_OTHER |
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49 | Priority-based, preemptive scheduling with timeslicing. Time quantums are |
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50 | maintained on a per-thread basis and are reset at each context switch. |
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51 | |
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52 | @item SCHED_SPORADIC |
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53 | Priority-based, preemptive scheduling utilizing three additional parameters: |
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54 | budget, replenishment period, and low priority. Under this policy, the |
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55 | thread is allowed to execute for "budget" amount of time before its priority |
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56 | is lowered to "low priority". At the end of each replenishment period, |
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57 | the thread resumes its initial priority and has its budget replenished. |
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58 | |
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59 | @end table |
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60 | |
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61 | @section Operations |
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62 | |
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63 | There is currently no text in this section. |
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64 | |
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65 | @section Directives |
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66 | |
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67 | This section details the scheduler manager's directives. |
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68 | A subsection is dedicated to each of this manager's directives |
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69 | and describes the calling sequence, related constants, usage, |
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70 | and status codes. |
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71 | |
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72 | @page |
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73 | @subsection sched_get_priority_min |
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74 | |
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75 | @subheading CALLING SEQUENCE: |
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76 | |
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77 | @example |
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78 | #include <sched.h> |
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79 | |
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80 | int sched_get_priority_min( |
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81 | int policy |
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82 | ); |
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83 | @end example |
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84 | |
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85 | @subheading STATUS CODES: |
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86 | |
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87 | On error, this routine returns -1 and sets errno to one of the following: |
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88 | |
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89 | @table @b |
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90 | @item EINVAL |
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91 | The indicated policy is invalid. |
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92 | |
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93 | @end table |
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94 | |
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95 | @subheading DESCRIPTION: |
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96 | |
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97 | @subheading NOTES: |
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98 | |
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99 | @page |
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100 | @subsection sched_get_priority_max |
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101 | |
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102 | @subheading CALLING SEQUENCE: |
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103 | |
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104 | @example |
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105 | #include <sched.h> |
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106 | |
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107 | int sched_get_priority_max( |
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108 | int policy |
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109 | ); |
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110 | @end example |
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111 | |
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112 | @subheading STATUS CODES: |
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113 | |
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114 | On error, this routine returns -1 and sets errno to one of the following: |
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115 | |
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116 | @table @b |
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117 | @item EINVAL |
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118 | The indicated policy is invalid. |
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119 | |
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120 | @end table |
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121 | |
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122 | @subheading DESCRIPTION: |
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123 | |
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124 | @subheading NOTES: |
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125 | |
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126 | @page |
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127 | @subsection sched_rr_get_interval |
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128 | |
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129 | @subheading CALLING SEQUENCE: |
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130 | |
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131 | @example |
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132 | #include <sched.h> |
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133 | |
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134 | int sched_rr_get_interval( |
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135 | pid_t pid, |
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136 | struct timespec *interval |
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137 | ); |
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138 | @end example |
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139 | |
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140 | @subheading STATUS CODES: |
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141 | |
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142 | On error, this routine returns -1 and sets errno to one of the following: |
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143 | |
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144 | @table @b |
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145 | @item ESRCH |
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146 | The indicated process id is invalid. |
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147 | |
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148 | @item EINVAL |
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149 | The specified interval pointer parameter is invalid. |
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150 | |
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151 | @end table |
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152 | |
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153 | @subheading DESCRIPTION: |
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154 | |
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155 | @subheading NOTES: |
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156 | |
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157 | @page |
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158 | @subsection sched_yield |
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159 | |
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160 | @subheading CALLING SEQUENCE: |
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161 | |
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162 | @example |
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163 | #include <sched.h> |
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164 | |
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165 | int sched_yield( void ); |
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166 | @end example |
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167 | |
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168 | @subheading STATUS CODES: |
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169 | |
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170 | This routine always returns zero to indicate success. |
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171 | |
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172 | @subheading DESCRIPTION: |
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173 | |
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174 | @subheading NOTES: |
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175 | |
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