1 | /** |
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2 | * @file |
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3 | * |
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4 | * @ingroup ScoreSMPLock |
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5 | * |
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6 | * @brief SMP Lock API |
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7 | */ |
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8 | |
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9 | /* |
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10 | * COPYRIGHT (c) 1989-2011. |
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11 | * On-Line Applications Research Corporation (OAR). |
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12 | * |
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13 | * Copyright (c) 2013-2014 embedded brains GmbH |
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14 | * |
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15 | * The license and distribution terms for this file may be |
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16 | * found in the file LICENSE in this distribution or at |
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17 | * http://www.rtems.org/license/LICENSE. |
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18 | */ |
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19 | |
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20 | #ifndef _RTEMS_SCORE_SMPLOCK_H |
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21 | #define _RTEMS_SCORE_SMPLOCK_H |
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22 | |
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23 | #include <rtems/score/cpuopts.h> |
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24 | |
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25 | #if defined( RTEMS_SMP ) |
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26 | |
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27 | #include <rtems/score/atomic.h> |
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28 | #include <rtems/score/isrlevel.h> |
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29 | |
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30 | #if defined( RTEMS_PROFILING ) |
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31 | #include <rtems/score/chainimpl.h> |
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32 | #include <string.h> |
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33 | #endif |
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34 | |
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35 | #ifdef __cplusplus |
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36 | extern "C" { |
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37 | #endif /* __cplusplus */ |
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38 | |
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39 | /** |
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40 | * @defgroup ScoreSMPLock SMP Locks |
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41 | * |
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42 | * @ingroup Score |
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43 | * |
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44 | * @brief The SMP lock provides mutual exclusion for SMP systems at the lowest |
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45 | * level. |
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46 | * |
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47 | * The SMP lock is implemented as a ticket lock. This provides fairness in |
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48 | * case of concurrent lock attempts. |
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49 | * |
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50 | * This SMP lock API uses a local context for acquire and release pairs. Such |
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51 | * a context may be used to implement for example the Mellor-Crummey and Scott |
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52 | * (MCS) locks in the future. |
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53 | * |
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54 | * @{ |
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55 | */ |
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56 | |
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57 | /** |
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58 | * @brief Count of lock contention counters for lock statistics. |
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59 | */ |
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60 | #define SMP_LOCK_STATS_CONTENTION_COUNTS 4 |
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61 | |
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62 | /** |
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63 | * @brief SMP lock statistics. |
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64 | * |
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65 | * The lock acquire attempt instant is the point in time right after the |
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66 | * interrupt disable action in the lock acquire sequence. |
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67 | * |
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68 | * The lock acquire instant is the point in time right after the lock |
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69 | * acquisition. This is the begin of the critical section code execution. |
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70 | * |
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71 | * The lock release instant is the point in time right before the interrupt |
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72 | * enable action in the lock release sequence. |
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73 | * |
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74 | * The lock section time is the time elapsed between the lock acquire instant |
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75 | * and the lock release instant. |
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76 | * |
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77 | * The lock acquire time is the time elapsed between the lock acquire attempt |
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78 | * instant and the lock acquire instant. |
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79 | */ |
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80 | typedef struct { |
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81 | #if defined( RTEMS_PROFILING ) |
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82 | /** |
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83 | * @brief Node for SMP lock statistics chain. |
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84 | */ |
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85 | Chain_Node Node; |
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86 | |
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87 | /** |
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88 | * @brief The maximum lock acquire time in CPU counter ticks. |
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89 | */ |
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90 | CPU_Counter_ticks max_acquire_time; |
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91 | |
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92 | /** |
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93 | * @brief The maximum lock section time in CPU counter ticks. |
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94 | */ |
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95 | CPU_Counter_ticks max_section_time; |
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96 | |
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97 | /** |
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98 | * @brief The count of lock uses. |
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99 | * |
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100 | * This value may overflow. |
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101 | */ |
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102 | uint64_t usage_count; |
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103 | |
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104 | /** |
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105 | * @brief Total lock acquire time in nanoseconds. |
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106 | * |
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107 | * The average lock acquire time is the total acquire time divided by the |
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108 | * lock usage count. The ration of the total section and total acquire times |
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109 | * gives a measure for the lock contention. |
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110 | * |
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111 | * This value may overflow. |
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112 | */ |
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113 | uint64_t total_acquire_time; |
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114 | |
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115 | /** |
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116 | * @brief The counts of lock acquire operations by contention. |
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117 | * |
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118 | * The contention count for index N corresponds to a lock acquire attempt |
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119 | * with an initial queue length of N. The last index corresponds to all |
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120 | * lock acquire attempts with an initial queue length greater than or equal |
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121 | * to SMP_LOCK_STATS_CONTENTION_COUNTS minus one. |
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122 | * |
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123 | * The values may overflow. |
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124 | */ |
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125 | uint64_t contention_counts[SMP_LOCK_STATS_CONTENTION_COUNTS]; |
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126 | |
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127 | /** |
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128 | * @brief Total lock section time in CPU counter ticks. |
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129 | * |
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130 | * The average lock section time is the total section time divided by the |
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131 | * lock usage count. |
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132 | * |
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133 | * This value may overflow. |
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134 | */ |
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135 | uint64_t total_section_time; |
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136 | |
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137 | /** |
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138 | * @brief The lock name. |
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139 | */ |
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140 | const char *name; |
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141 | #endif /* defined( RTEMS_PROFILING ) */ |
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142 | } SMP_lock_Stats; |
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143 | |
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144 | /** |
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145 | * @brief Local context for SMP lock statistics. |
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146 | */ |
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147 | typedef struct { |
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148 | #if defined( RTEMS_PROFILING ) |
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149 | /** |
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150 | * @brief The last lock acquire instant in CPU counter ticks. |
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151 | * |
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152 | * This value is used to measure the lock section time. |
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153 | */ |
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154 | CPU_Counter_ticks acquire_instant; |
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155 | #endif |
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156 | } SMP_lock_Stats_context; |
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157 | |
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158 | /** |
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159 | * @brief SMP lock statistics initializer for static initialization. |
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160 | */ |
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161 | #if defined( RTEMS_PROFILING ) |
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162 | #define SMP_LOCK_STATS_INITIALIZER( name ) \ |
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163 | { { NULL, NULL }, 0, 0, 0, 0, { 0, 0, 0, 0 }, 0, name } |
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164 | #else |
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165 | #define SMP_LOCK_STATS_INITIALIZER( name ) \ |
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166 | { } |
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167 | #endif |
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168 | |
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169 | /** |
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170 | * @brief Initializes an SMP lock statistics block. |
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171 | * |
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172 | * @param[in, out] stats The SMP lock statistics block. |
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173 | * @param[in] name The name for the SMP lock statistics. This name must be |
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174 | * persistent throughout the life time of this statistics block. |
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175 | */ |
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176 | static inline void _SMP_lock_Stats_initialize( |
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177 | SMP_lock_Stats *stats, |
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178 | const char *name |
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179 | ) |
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180 | { |
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181 | SMP_lock_Stats init = SMP_LOCK_STATS_INITIALIZER( name ); |
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182 | |
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183 | *stats = init; |
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184 | } |
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185 | |
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186 | /** |
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187 | * @brief Destroys an SMP lock statistics block. |
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188 | * |
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189 | * @param[in,out] stats The SMP lock statistics block. |
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190 | */ |
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191 | static inline void _SMP_lock_Stats_destroy( SMP_lock_Stats *stats ); |
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192 | |
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193 | /** |
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194 | * @brief Destroys an SMP lock statistics block. |
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195 | * |
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196 | * @param[in,out] stats The SMP lock statistics block. |
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197 | * @param[in] stats_context The SMP lock statistics context. |
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198 | */ |
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199 | static inline void _SMP_lock_Stats_release_update( |
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200 | SMP_lock_Stats *stats, |
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201 | const SMP_lock_Stats_context *stats_context |
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202 | ); |
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203 | |
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204 | /** |
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205 | * @brief SMP ticket lock control. |
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206 | */ |
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207 | typedef struct { |
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208 | Atomic_Uint next_ticket; |
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209 | Atomic_Uint now_serving; |
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210 | SMP_lock_Stats Stats; |
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211 | } SMP_ticket_lock_Control; |
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212 | |
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213 | /** |
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214 | * @brief SMP ticket lock control initializer for static initialization. |
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215 | */ |
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216 | #define SMP_TICKET_LOCK_INITIALIZER( name ) \ |
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217 | { \ |
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218 | ATOMIC_INITIALIZER_UINT( 0U ), \ |
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219 | ATOMIC_INITIALIZER_UINT( 0U ), \ |
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220 | SMP_LOCK_STATS_INITIALIZER( name ) \ |
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221 | } |
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222 | |
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223 | /** |
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224 | * @brief Initializes an SMP ticket lock. |
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225 | * |
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226 | * Concurrent initialization leads to unpredictable results. |
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227 | * |
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228 | * @param[in,out] lock The SMP ticket lock control. |
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229 | * @param[in] name The name for the SMP ticket lock. This name must be |
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230 | * persistent throughout the life time of this lock. |
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231 | */ |
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232 | static inline void _SMP_ticket_lock_Initialize( |
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233 | SMP_ticket_lock_Control *lock, |
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234 | const char *name |
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235 | ) |
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236 | { |
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237 | _Atomic_Init_uint( &lock->next_ticket, 0U ); |
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238 | _Atomic_Init_uint( &lock->now_serving, 0U ); |
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239 | _SMP_lock_Stats_initialize( &lock->Stats, name ); |
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240 | } |
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241 | |
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242 | /** |
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243 | * @brief Destroys an SMP ticket lock. |
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244 | * |
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245 | * Concurrent destruction leads to unpredictable results. |
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246 | * |
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247 | * @param[in,out] lock The SMP ticket lock control. |
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248 | */ |
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249 | static inline void _SMP_ticket_lock_Destroy( SMP_ticket_lock_Control *lock ) |
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250 | { |
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251 | _SMP_lock_Stats_destroy( &lock->Stats ); |
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252 | } |
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253 | |
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254 | /** |
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255 | * @brief Acquires an SMP ticket lock. |
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256 | * |
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257 | * This function will not disable interrupts. The caller must ensure that the |
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258 | * current thread of execution is not interrupted indefinite once it obtained |
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259 | * the SMP ticket lock. |
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260 | * |
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261 | * @param[in,out] lock The SMP ticket lock control. |
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262 | * @param[out] stats_context The SMP lock statistics context. |
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263 | */ |
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264 | static inline void _SMP_ticket_lock_Acquire( |
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265 | SMP_ticket_lock_Control *lock, |
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266 | SMP_lock_Stats_context *stats_context |
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267 | ) |
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268 | { |
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269 | unsigned int my_ticket; |
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270 | unsigned int now_serving; |
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271 | |
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272 | #if defined( RTEMS_PROFILING ) |
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273 | SMP_lock_Stats *stats = &lock->Stats; |
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274 | CPU_Counter_ticks first; |
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275 | CPU_Counter_ticks second; |
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276 | CPU_Counter_ticks delta; |
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277 | unsigned int initial_queue_length; |
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278 | |
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279 | first = _CPU_Counter_read(); |
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280 | #endif |
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281 | |
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282 | my_ticket = |
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283 | _Atomic_Fetch_add_uint( &lock->next_ticket, 1U, ATOMIC_ORDER_ACQ_REL ); |
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284 | |
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285 | #if defined( RTEMS_PROFILING ) |
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286 | now_serving = |
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287 | _Atomic_Load_uint( &lock->now_serving, ATOMIC_ORDER_ACQUIRE ); |
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288 | initial_queue_length = my_ticket - now_serving; |
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289 | |
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290 | if ( initial_queue_length > 0 ) { |
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291 | #endif |
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292 | |
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293 | do { |
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294 | now_serving = |
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295 | _Atomic_Load_uint( &lock->now_serving, ATOMIC_ORDER_ACQUIRE ); |
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296 | } while ( now_serving != my_ticket ); |
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297 | |
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298 | #if defined( RTEMS_PROFILING ) |
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299 | } |
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300 | |
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301 | second = _CPU_Counter_read(); |
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302 | stats_context->acquire_instant = second; |
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303 | delta = _CPU_Counter_difference( second, first ); |
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304 | |
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305 | ++stats->usage_count; |
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306 | |
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307 | stats->total_acquire_time += delta; |
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308 | |
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309 | if ( stats->max_acquire_time < delta ) { |
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310 | stats->max_acquire_time = delta; |
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311 | } |
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312 | |
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313 | if ( initial_queue_length >= SMP_LOCK_STATS_CONTENTION_COUNTS ) { |
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314 | initial_queue_length = SMP_LOCK_STATS_CONTENTION_COUNTS - 1; |
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315 | } |
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316 | ++stats->contention_counts[initial_queue_length]; |
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317 | #else |
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318 | (void) stats_context; |
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319 | #endif |
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320 | } |
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321 | |
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322 | /** |
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323 | * @brief Releases an SMP ticket lock. |
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324 | * |
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325 | * @param[in,out] lock The SMP ticket lock control. |
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326 | * @param[in] stats_context The SMP lock statistics context. |
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327 | */ |
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328 | static inline void _SMP_ticket_lock_Release( |
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329 | SMP_ticket_lock_Control *lock, |
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330 | const SMP_lock_Stats_context *stats_context |
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331 | ) |
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332 | { |
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333 | unsigned int current_ticket = |
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334 | _Atomic_Load_uint( &lock->now_serving, ATOMIC_ORDER_RELAXED ); |
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335 | unsigned int next_ticket = current_ticket + 1U; |
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336 | |
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337 | _SMP_lock_Stats_release_update( &lock->Stats, stats_context ); |
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338 | |
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339 | _Atomic_Store_uint( &lock->now_serving, next_ticket, ATOMIC_ORDER_RELEASE ); |
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340 | } |
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341 | |
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342 | /** |
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343 | * @brief SMP lock control. |
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344 | */ |
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345 | typedef struct { |
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346 | SMP_ticket_lock_Control ticket_lock; |
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347 | } SMP_lock_Control; |
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348 | |
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349 | /** |
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350 | * @brief Local SMP lock context for acquire and release pairs. |
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351 | */ |
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352 | typedef struct { |
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353 | ISR_Level isr_level; |
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354 | SMP_lock_Stats_context Stats_context; |
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355 | } SMP_lock_Context; |
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356 | |
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357 | /** |
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358 | * @brief SMP lock control initializer for static initialization. |
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359 | */ |
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360 | #define SMP_LOCK_INITIALIZER( name ) { SMP_TICKET_LOCK_INITIALIZER( name ) } |
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361 | |
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362 | /** |
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363 | * @brief Initializes an SMP lock. |
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364 | * |
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365 | * Concurrent initialization leads to unpredictable results. |
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366 | * |
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367 | * @param[in,out] lock The SMP lock control. |
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368 | * @param[in] name The name for the SMP lock statistics. This name must be |
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369 | * persistent throughout the life time of this statistics block. |
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370 | */ |
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371 | static inline void _SMP_lock_Initialize( |
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372 | SMP_lock_Control *lock, |
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373 | const char *name |
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374 | ) |
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375 | { |
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376 | _SMP_ticket_lock_Initialize( &lock->ticket_lock, name ); |
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377 | } |
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378 | |
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379 | /** |
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380 | * @brief Destroys an SMP lock. |
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381 | * |
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382 | * Concurrent destruction leads to unpredictable results. |
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383 | * |
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384 | * @param[in,out] lock The SMP lock control. |
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385 | */ |
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386 | static inline void _SMP_lock_Destroy( SMP_lock_Control *lock ) |
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387 | { |
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388 | _SMP_ticket_lock_Destroy( &lock->ticket_lock ); |
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389 | } |
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390 | |
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391 | /** |
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392 | * @brief Acquires an SMP lock. |
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393 | * |
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394 | * This function will not disable interrupts. The caller must ensure that the |
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395 | * current thread of execution is not interrupted indefinite once it obtained |
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396 | * the SMP lock. |
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397 | * |
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398 | * @param[in,out] lock The SMP lock control. |
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399 | * @param[in,out] context The local SMP lock context for an acquire and release |
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400 | * pair. |
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401 | */ |
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402 | static inline void _SMP_lock_Acquire( |
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403 | SMP_lock_Control *lock, |
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404 | SMP_lock_Context *context |
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405 | ) |
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406 | { |
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407 | (void) context; |
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408 | _SMP_ticket_lock_Acquire( &lock->ticket_lock, &context->Stats_context ); |
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409 | } |
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410 | |
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411 | /** |
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412 | * @brief Releases an SMP lock. |
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413 | * |
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414 | * @param[in,out] lock The SMP lock control. |
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415 | * @param[in,out] context The local SMP lock context for an acquire and release |
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416 | * pair. |
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417 | */ |
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418 | static inline void _SMP_lock_Release( |
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419 | SMP_lock_Control *lock, |
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420 | SMP_lock_Context *context |
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421 | ) |
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422 | { |
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423 | (void) context; |
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424 | _SMP_ticket_lock_Release( &lock->ticket_lock, &context->Stats_context ); |
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425 | } |
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426 | |
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427 | /** |
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428 | * @brief Disables interrupts and acquires the SMP lock. |
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429 | * |
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430 | * @param[in,out] lock The SMP lock control. |
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431 | * @param[in,out] context The local SMP lock context for an acquire and release |
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432 | * pair. |
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433 | */ |
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434 | static inline void _SMP_lock_ISR_disable_and_acquire( |
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435 | SMP_lock_Control *lock, |
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436 | SMP_lock_Context *context |
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437 | ) |
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438 | { |
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439 | _ISR_Disable_without_giant( context->isr_level ); |
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440 | _SMP_lock_Acquire( lock, context ); |
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441 | } |
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442 | |
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443 | /** |
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444 | * @brief Releases the SMP lock and enables interrupts. |
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445 | * |
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446 | * @param[in,out] lock The SMP lock control. |
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447 | * @param[in,out] context The local SMP lock context for an acquire and release |
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448 | * pair. |
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449 | */ |
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450 | static inline void _SMP_lock_Release_and_ISR_enable( |
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451 | SMP_lock_Control *lock, |
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452 | SMP_lock_Context *context |
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453 | ) |
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454 | { |
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455 | _SMP_lock_Release( lock, context ); |
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456 | _ISR_Enable_without_giant( context->isr_level ); |
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457 | } |
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458 | |
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459 | #if defined( RTEMS_PROFILING ) |
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460 | typedef struct { |
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461 | SMP_lock_Control Lock; |
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462 | Chain_Control Stats_chain; |
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463 | Chain_Control Iterator_chain; |
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464 | } SMP_lock_Stats_control; |
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465 | |
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466 | typedef struct { |
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467 | Chain_Node Node; |
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468 | SMP_lock_Stats *current; |
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469 | } SMP_lock_Stats_iteration_context; |
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470 | |
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471 | extern SMP_lock_Stats_control _SMP_lock_Stats_control; |
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472 | |
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473 | static inline void _SMP_lock_Stats_iteration_start( |
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474 | SMP_lock_Stats_iteration_context *iteration_context |
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475 | ) |
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476 | { |
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477 | SMP_lock_Stats_control *control = &_SMP_lock_Stats_control; |
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478 | SMP_lock_Context lock_context; |
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479 | |
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480 | _SMP_lock_ISR_disable_and_acquire( &control->Lock, &lock_context ); |
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481 | |
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482 | _Chain_Append_unprotected( |
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483 | &control->Iterator_chain, |
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484 | &iteration_context->Node |
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485 | ); |
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486 | iteration_context->current = |
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487 | (SMP_lock_Stats *) _Chain_First( &control->Stats_chain ); |
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488 | |
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489 | _SMP_lock_Release_and_ISR_enable( &control->Lock, &lock_context ); |
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490 | } |
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491 | |
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492 | static inline bool _SMP_lock_Stats_iteration_next( |
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493 | SMP_lock_Stats_iteration_context *iteration_context, |
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494 | SMP_lock_Stats *snapshot, |
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495 | char *name, |
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496 | size_t name_size |
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497 | ) |
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498 | { |
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499 | SMP_lock_Stats_control *control = &_SMP_lock_Stats_control; |
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500 | SMP_lock_Context lock_context; |
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501 | SMP_lock_Stats *current; |
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502 | bool valid; |
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503 | |
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504 | _SMP_lock_ISR_disable_and_acquire( &control->Lock, &lock_context ); |
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505 | |
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506 | current = iteration_context->current; |
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507 | if ( !_Chain_Is_tail( &control->Stats_chain, ¤t->Node ) ) { |
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508 | size_t name_len = strlen(current->name); |
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509 | |
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510 | valid = true; |
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511 | |
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512 | iteration_context->current = (SMP_lock_Stats *) |
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513 | _Chain_Next( ¤t->Node ); |
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514 | |
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515 | *snapshot = *current; |
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516 | snapshot->name = name; |
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517 | |
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518 | if ( name_len >= name_size ) { |
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519 | name_len = name_size - 1; |
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520 | } |
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521 | |
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522 | name[name_len] = '\0'; |
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523 | memcpy(name, current->name, name_len); |
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524 | } else { |
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525 | valid = false; |
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526 | } |
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527 | |
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528 | _SMP_lock_Release_and_ISR_enable( &control->Lock, &lock_context ); |
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529 | |
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530 | return valid; |
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531 | } |
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532 | |
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533 | static inline void _SMP_lock_Stats_iteration_stop( |
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534 | SMP_lock_Stats_iteration_context *iteration_context |
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535 | ) |
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536 | { |
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537 | SMP_lock_Stats_control *control = &_SMP_lock_Stats_control; |
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538 | SMP_lock_Context lock_context; |
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539 | |
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540 | _SMP_lock_ISR_disable_and_acquire( &control->Lock, &lock_context ); |
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541 | _Chain_Extract_unprotected( &iteration_context->Node ); |
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542 | _SMP_lock_Release_and_ISR_enable( &control->Lock, &lock_context ); |
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543 | } |
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544 | #endif |
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545 | |
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546 | static inline void _SMP_lock_Stats_destroy( SMP_lock_Stats *stats ) |
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547 | { |
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548 | #if defined( RTEMS_PROFILING ) |
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549 | if ( !_Chain_Is_node_off_chain( &stats->Node ) ) { |
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550 | SMP_lock_Stats_control *control = &_SMP_lock_Stats_control; |
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551 | SMP_lock_Context lock_context; |
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552 | SMP_lock_Stats_iteration_context *iteration_context; |
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553 | SMP_lock_Stats_iteration_context *iteration_context_tail; |
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554 | SMP_lock_Stats *next_stats; |
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555 | |
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556 | _SMP_lock_ISR_disable_and_acquire( &control->Lock, &lock_context ); |
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557 | |
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558 | next_stats = (SMP_lock_Stats *) _Chain_Next( &stats->Node ); |
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559 | _Chain_Extract_unprotected( &stats->Node ); |
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560 | |
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561 | iteration_context = (SMP_lock_Stats_iteration_context *) |
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562 | _Chain_First( &control->Iterator_chain ); |
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563 | iteration_context_tail = (SMP_lock_Stats_iteration_context *) |
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564 | _Chain_Tail( &control->Iterator_chain ); |
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565 | |
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566 | while ( iteration_context != iteration_context_tail ) { |
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567 | if ( iteration_context->current == stats ) { |
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568 | iteration_context->current = next_stats; |
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569 | } |
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570 | |
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571 | iteration_context = (SMP_lock_Stats_iteration_context *) |
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572 | _Chain_Next( &iteration_context->Node ); |
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573 | } |
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574 | |
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575 | _SMP_lock_Release_and_ISR_enable( &control->Lock, &lock_context ); |
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576 | } |
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577 | #else |
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578 | (void) stats; |
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579 | #endif |
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580 | } |
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581 | |
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582 | static inline void _SMP_lock_Stats_release_update( |
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583 | SMP_lock_Stats *stats, |
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584 | const SMP_lock_Stats_context *stats_context |
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585 | ) |
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586 | { |
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587 | #if defined( RTEMS_PROFILING ) |
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588 | CPU_Counter_ticks first = stats_context->acquire_instant; |
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589 | CPU_Counter_ticks second = _CPU_Counter_read(); |
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590 | CPU_Counter_ticks delta = _CPU_Counter_difference( second, first ); |
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591 | |
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592 | stats->total_section_time += delta; |
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593 | |
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594 | if ( stats->max_section_time < delta ) { |
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595 | stats->max_section_time = delta; |
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596 | |
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597 | if ( _Chain_Is_node_off_chain( &stats->Node ) ) { |
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598 | SMP_lock_Stats_control *control = &_SMP_lock_Stats_control; |
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599 | SMP_lock_Context lock_context; |
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600 | |
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601 | _SMP_lock_ISR_disable_and_acquire( &control->Lock, &lock_context ); |
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602 | _Chain_Append_unprotected( &control->Stats_chain, &stats->Node ); |
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603 | _SMP_lock_Release_and_ISR_enable( &control->Lock, &lock_context ); |
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604 | } |
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605 | } |
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606 | #else |
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607 | (void) stats; |
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608 | (void) stats_context; |
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609 | #endif |
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610 | } |
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611 | |
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612 | /**@}*/ |
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613 | |
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614 | #ifdef __cplusplus |
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615 | } |
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616 | #endif /* __cplusplus */ |
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617 | |
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618 | #endif /* defined( RTEMS_SMP ) */ |
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619 | |
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620 | #endif /* _RTEMS_SCORE_SMPLOCK_H */ |
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