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1 //========================================================================== |
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2 // |
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3 // sched/sched.cxx |
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4 // |
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5 // Scheduler class implementations |
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6 // |
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7 //========================================================================== |
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8 //####COPYRIGHTBEGIN#### |
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9 // |
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10 // ------------------------------------------- |
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11 // The contents of this file are subject to the Cygnus eCos Public License |
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12 // Version 1.0 (the "License"); you may not use this file except in |
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13 // compliance with the License. You may obtain a copy of the License at |
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14 // http://sourceware.cygnus.com/ecos |
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15 // |
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16 // Software distributed under the License is distributed on an "AS IS" |
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17 // basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the |
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18 // License for the specific language governing rights and limitations under |
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19 // the License. |
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20 // |
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21 // The Original Code is eCos - Embedded Cygnus Operating System, released |
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22 // September 30, 1998. |
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23 // |
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24 // The Initial Developer of the Original Code is Cygnus. Portions created |
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25 // by Cygnus are Copyright (C) 1998,1999 Cygnus Solutions. All Rights Reserved. |
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26 // ------------------------------------------- |
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27 // |
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28 //####COPYRIGHTEND#### |
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29 //========================================================================== |
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30 //#####DESCRIPTIONBEGIN#### |
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31 // |
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32 // Author(s): nickg |
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33 // Contributors: nickg |
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34 // Date: 1997-09-15 |
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35 // Purpose: Scheduler class implementation |
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36 // Description: This file contains the definitions of the scheduler class |
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37 // member functions that are common to all scheduler |
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38 // implementations. |
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39 // |
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40 //####DESCRIPTIONEND#### |
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41 // |
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42 //========================================================================== |
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43 |
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44 #include <pkgconf/kernel.h> |
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45 |
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46 #include <cyg/kernel/ktypes.h> // base kernel types |
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47 #include <cyg/infra/cyg_trac.h> // tracing macros |
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48 #include <cyg/infra/cyg_ass.h> // assertion macros |
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49 #include <cyg/kernel/instrmnt.h> // instrumentation |
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50 |
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51 #include <cyg/kernel/sched.hxx> // our header |
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52 |
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53 #include <cyg/kernel/thread.hxx> // thread classes |
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54 #include <cyg/kernel/intr.hxx> // Interrupt interface |
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55 |
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56 #include <cyg/hal/hal_arch.h> // Architecture specific definitions |
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57 |
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58 #include <cyg/kernel/thread.inl> // thread inlines |
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59 |
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60 //------------------------------------------------------------------------- |
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61 // Some local tracing control - a default. |
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62 #ifdef CYGDBG_USE_TRACING |
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63 # if !defined( CYGDBG_INFRA_DEBUG_TRACE_ASSERT_SIMPLE ) && \ |
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64 !defined( CYGDBG_INFRA_DEBUG_TRACE_ASSERT_FANCY ) |
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65 // ie. not a tracing implementation that takes a long time to output |
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66 |
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67 # ifndef CYGDBG_KERNEL_TRACE_UNLOCK_INNER |
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68 # define CYGDBG_KERNEL_TRACE_UNLOCK_INNER |
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69 # endif // control not already defined |
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70 |
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71 # endif // trace implementation not ..._SIMPLE && not ..._FANCY |
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72 #endif // CYGDBG_USE_TRACING |
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73 |
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74 // ------------------------------------------------------------------------- |
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75 // Static Cyg_Scheduler class members |
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76 |
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77 // We start with sched_lock at 1 so that any kernel code we |
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78 // call during initialization will not try to reschedule. |
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79 |
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80 volatile cyg_ucount32 Cyg_Scheduler_Base::sched_lock = 1; |
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81 |
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82 Cyg_Thread *Cyg_Scheduler_Base::current_thread = NULL; |
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83 |
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84 cyg_bool Cyg_Scheduler_Base::need_reschedule = false; |
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85 |
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86 Cyg_Scheduler Cyg_Scheduler::scheduler CYG_INIT_PRIORITY( SCHEDULER ); |
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87 |
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88 cyg_ucount32 Cyg_Scheduler_Base::thread_switches = 0; |
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89 |
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90 // ------------------------------------------------------------------------- |
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91 // Scheduler unlock function. |
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92 // This is only called when the lock is to be decremented to zero and there |
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93 // is the potential for real work to be done. Other cases are handled in |
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94 // Cyg_Scheduler::unlock() which is an inline. |
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95 |
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96 void Cyg_Scheduler::unlock_inner() |
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97 { |
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98 #ifdef CYGDBG_KERNEL_TRACE_UNLOCK_INNER |
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99 CYG_REPORT_FUNCTION(); |
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100 #endif |
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101 |
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102 do { |
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103 |
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104 CYG_PRECONDITION( sched_lock == 1 , "sched_lock not 1" ); |
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105 |
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106 #ifdef CYGIMP_KERNEL_INTERRUPTS_DSRS |
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107 |
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108 // Call any pending DSRs. Do this here to ensure that any |
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109 // threads that get awakened are properly scheduled. |
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110 |
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111 if( Cyg_Interrupt::DSRs_pending() ) |
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112 Cyg_Interrupt::call_pending_DSRs(); |
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113 #endif |
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114 |
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115 Cyg_Thread *current = current_thread; |
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116 |
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117 CYG_ASSERTCLASS( current, "Bad current thread" ); |
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118 |
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119 // If the current thread is going to sleep, or someone |
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120 // wants a reschedule, choose another thread to run |
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121 |
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122 if( current->state != Cyg_Thread::RUNNING || need_reschedule ) { |
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123 |
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124 CYG_INSTRUMENT_SCHED(RESCHEDULE,0,0); |
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125 |
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126 // Get the next thread to run from scheduler |
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127 Cyg_Thread *next = scheduler.schedule(); |
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128 |
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129 CYG_CHECK_DATA_PTR( next, "Invalid next thread pointer"); |
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130 CYG_ASSERTCLASS( next, "Bad next thread" ); |
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131 |
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132 if( current != next ) |
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133 { |
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134 |
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135 CYG_INSTRUMENT_THREAD(SWITCH,current,next); |
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136 |
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137 // Count this thread switch |
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138 thread_switches++; |
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139 |
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140 // Switch contexts |
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141 HAL_THREAD_SWITCH_CONTEXT( ¤t->stack_ptr, |
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142 &next->stack_ptr ); |
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143 |
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144 // Worry here about possible compiler |
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145 // optimizations across the above call that may try to |
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146 // propogate common subexpresions. We would end up |
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147 // with the expression from one thread in its |
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148 // successor. This is only a worry if we do not save |
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149 // and restore the complete register set. We need a |
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150 // way of marking functions that return into a |
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151 // different context. A temporary fix would be to |
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152 // disable CSE (-fdisable-cse) in the compiler. |
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153 |
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154 // We return here only when the current thread is |
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155 // rescheduled. There is a bit of housekeeping to do |
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156 // here before we are allowed to go on our way. |
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157 |
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158 CYG_CHECK_DATA_PTR( current, "Invalid current thread pointer"); |
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159 CYG_ASSERTCLASS( current, "Bad current thread" ); |
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160 |
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161 current_thread = current; // restore current thread pointer |
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162 |
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163 } |
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164 |
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165 #ifdef CYGSEM_KERNEL_SCHED_TIMESLICE |
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166 // Reset the timeslice counter so that this thread gets a full |
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167 // quantum. |
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168 reset_timeslice_count(); |
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169 #endif |
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170 |
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171 need_reschedule = false; // finished rescheduling |
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172 } |
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173 |
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174 HAL_REORDER_BARRIER(); // Make sure everything above has happened |
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175 // by this point |
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176 sched_lock = 0; // Clear the lock |
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177 HAL_REORDER_BARRIER(); |
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178 |
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179 #ifdef CYGIMP_KERNEL_INTERRUPTS_DSRS |
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180 |
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181 // Now check whether any DSRs got posted during the thread |
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182 // switch and if so, go around again. Making this test after |
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183 // the lock has been zeroed avoids a race condition in which |
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184 // a DSR could have been posted during a reschedule, but would |
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185 // not be run until the _next_ time we release the sched lock. |
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186 |
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187 if( Cyg_Interrupt::DSRs_pending() ) { |
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188 sched_lock = 1; // reclaim the lock |
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189 continue; // go back to head of loop |
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190 } |
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191 |
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192 #endif |
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193 // Otherwise the lock is zero, we can return. |
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194 |
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195 CYG_POSTCONDITION( sched_lock == 0, "sched_lock not zero" ); |
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196 |
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197 #ifdef CYGDBG_KERNEL_TRACE_UNLOCK_INNER |
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198 CYG_REPORT_RETURN(); |
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199 #endif |
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200 return; |
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201 |
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202 } while( 1 ); |
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203 |
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204 CYG_FAIL( "Should not be executed" ); |
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205 } |
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206 |
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207 // ------------------------------------------------------------------------- |
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208 // Start the scheduler. This is called after the initial threads have been |
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209 // created to start scheduling. |
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210 |
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211 void Cyg_Scheduler::start() |
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212 { |
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213 CYG_REPORT_FUNCTION(); |
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214 |
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215 // Get the first thread to run from scheduler |
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216 register Cyg_Thread *next = scheduler.schedule(); |
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217 |
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218 CYG_ASSERTCLASS( next, "Bad initial thread" ); |
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219 |
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220 need_reschedule = false; // finished rescheduling |
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221 current_thread = next; // restore current thread pointer |
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222 |
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223 #ifdef CYGVAR_KERNEL_COUNTERS_CLOCK |
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224 // Reference the real time clock. This ensures that at least one |
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225 // reference to the kernel_clock.o object exists, without which |
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226 // the object will not be included while linking. |
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227 CYG_REFERENCE_OBJECT( Cyg_Clock::real_time_clock ); |
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228 #endif |
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229 |
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230 // Let the interrupts go |
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231 Cyg_Interrupt::enable_interrupts(); |
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232 |
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233 HAL_THREAD_LOAD_CONTEXT( &next->stack_ptr ); |
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234 |
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235 } |
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236 |
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237 // ------------------------------------------------------------------------- |
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238 // Consistency checker |
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239 |
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240 #ifdef CYGDBG_USE_ASSERTS |
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241 |
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242 bool Cyg_Scheduler::check_this( cyg_assert_class_zeal zeal) const |
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243 { |
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244 CYG_REPORT_FUNCTION(); |
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245 |
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246 // check that we have a non-NULL pointer first |
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247 if( this == NULL ) return false; |
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248 |
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249 switch( zeal ) |
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250 { |
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251 case cyg_system_test: |
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252 case cyg_extreme: |
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253 case cyg_thorough: |
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254 if( !current_thread->check_this(zeal) ) return false; |
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255 case cyg_quick: |
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256 case cyg_trivial: |
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257 case cyg_none: |
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258 default: |
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259 break; |
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260 }; |
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261 |
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262 return true; |
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263 } |
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264 |
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265 #endif |
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266 |
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267 //========================================================================== |
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268 // SchedThread members |
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269 |
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270 // ------------------------------------------------------------------------- |
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271 // Constructor |
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272 |
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273 Cyg_SchedThread::Cyg_SchedThread(Cyg_Thread *thread, CYG_ADDRWORD sched_info) |
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274 : Cyg_SchedThread_Implementation(sched_info) |
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275 { |
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276 CYG_REPORT_FUNCTION(); |
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277 |
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278 queue = NULL; |
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279 |
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280 if( Cyg_Scheduler::current_thread == NULL ) |
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281 Cyg_Scheduler::current_thread = thread; |
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282 |
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283 #ifdef CYGSEM_KERNEL_SYNCH_MUTEX_PRIORITY_INHERITANCE_SIMPLE |
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284 |
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285 mutex_count = 0; |
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286 priority_inherited = false; |
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287 |
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288 #endif |
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289 |
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290 } |
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291 |
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292 // ------------------------------------------------------------------------- |
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293 // Priority inheritance support. |
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294 |
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295 #ifdef CYGSEM_KERNEL_SYNCH_MUTEX_PRIORITY_INHERITANCE |
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296 |
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297 // ------------------------------------------------------------------------- |
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298 // Inherit the priority of the provided thread if it |
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299 // has a higher priority than ours. |
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300 |
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301 void Cyg_SchedThread::inherit_priority( Cyg_Thread *thread) |
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302 { |
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303 #ifdef CYGSEM_KERNEL_SYNCH_MUTEX_PRIORITY_INHERITANCE_SIMPLE |
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304 |
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305 // A simple implementation of priority inheritance. If the other |
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306 // thread is of higher priority, reset our priority to his. The |
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307 // first time we do this, save our original priority. |
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308 |
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309 Cyg_Thread *self = CYG_CLASSFROMBASE(Cyg_Thread, |
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310 Cyg_SchedThread, |
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311 this); |
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312 |
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313 CYG_ASSERT( mutex_count > 0, "Non-positive mutex count"); |
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314 CYG_ASSERT( self != thread, "Trying to inherit from self!"); |
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315 |
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316 if( thread->get_priority() < priority ) |
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317 { |
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318 cyg_priority mypri = priority; |
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319 |
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320 if( !priority_inherited ) |
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321 { |
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322 // If this is first inheritance, copy the old pri |
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323 // and set inherited flag. We do this after setting the |
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324 // pri since set_priority() is inheritance aware. |
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325 |
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326 self->set_priority( thread->get_priority() ); |
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327 priority_inherited = true, |
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328 original_priority = mypri; |
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329 } |
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330 else |
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331 { |
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332 // Already in inherited state, and new pri is higher |
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333 // than old. Just change the pri. |
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334 |
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335 self->set_priority( thread->get_priority() ); |
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336 } |
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337 } |
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338 |
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339 #endif |
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340 } |
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341 |
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342 // ------------------------------------------------------------------------- |
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343 // Lose a priority inheritance |
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344 |
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345 void Cyg_SchedThread::disinherit_priority() |
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346 { |
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347 #ifdef CYGSEM_KERNEL_SYNCH_MUTEX_PRIORITY_INHERITANCE_SIMPLE |
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348 |
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349 // A simple implementation of priority inheritance. The |
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350 // simplification in this algorithm is that we do not reduce our |
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351 // priority until we have freed all mutexes claimed. Hence we can |
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352 // continue to run at an artificially high priority even when we |
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353 // should not. However, since nested mutexes are rare, the thread |
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354 // we have inherited from is likely to be locking the same mutexes |
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355 // we are, and mutex claim periods should be very short, the |
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356 // performance difference between this and a more complex algorithm |
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357 // should be negligible. The most important advantage of this |
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358 // algorithm is that it is fast and deterministic. |
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359 |
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360 Cyg_Thread *self = CYG_CLASSFROMBASE(Cyg_Thread, |
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361 Cyg_SchedThread, |
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362 this); |
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363 |
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364 CYG_ASSERT( mutex_count >= 0, "Non-positive mutex count"); |
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365 |
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366 if( mutex_count == 0 && priority_inherited ) |
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367 { |
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368 priority_inherited = false; |
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369 |
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370 // Only make an effort if the priority must change |
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371 if( priority < original_priority ) |
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372 self->set_priority( original_priority ); |
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373 |
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374 } |
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375 |
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376 #endif |
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377 } |
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378 |
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379 #endif |
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380 |
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381 // ------------------------------------------------------------------------- |
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382 // EOF sched/sched.cxx |
