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1 /* |
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2 * Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved. |
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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4 * |
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5 * This code is free software; you can redistribute it and/or modify it |
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6 * under the terms of the GNU General Public License version 2 only, as |
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7 * published by the Free Software Foundation. |
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8 * |
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9 * This code is distributed in the hope that it will be useful, but WITHOUT |
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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12 * version 2 for more details (a copy is included in the LICENSE file that |
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13 * accompanied this code). |
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14 * |
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15 * You should have received a copy of the GNU General Public License version |
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16 * 2 along with this work; if not, write to the Free Software Foundation, |
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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18 * |
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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20 * or visit www.oracle.com if you need additional information or have any |
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21 * questions. |
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22 * |
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23 */ |
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24 |
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25 #include "precompiled.hpp" |
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26 #include "rdtsc_x86.hpp" |
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27 #include "runtime/thread.inline.hpp" |
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28 #include "vm_version_ext_x86.hpp" |
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29 |
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30 // The following header contains the implementations of rdtsc() |
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31 #include OS_CPU_HEADER_INLINE(os) |
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32 |
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33 static jlong _epoch = 0; |
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34 static bool rdtsc_elapsed_counter_enabled = false; |
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35 static jlong tsc_frequency = 0; |
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36 |
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37 static jlong set_epoch() { |
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38 assert(0 == _epoch, "invariant"); |
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39 _epoch = os::rdtsc(); |
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40 return _epoch; |
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41 } |
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42 |
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43 // Base loop to estimate ticks frequency for tsc counter from user mode. |
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44 // Volatiles and sleep() are used to prevent compiler from applying optimizations. |
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45 static void do_time_measurements(volatile jlong& time_base, |
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46 volatile jlong& time_fast, |
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47 volatile jlong& time_base_elapsed, |
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48 volatile jlong& time_fast_elapsed) { |
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49 static const unsigned int FT_SLEEP_MILLISECS = 1; |
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50 const unsigned int loopcount = 3; |
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51 |
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52 volatile jlong start = 0; |
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53 volatile jlong fstart = 0; |
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54 volatile jlong end = 0; |
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55 volatile jlong fend = 0; |
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56 |
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57 // Figure out the difference between rdtsc and os provided timer. |
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58 // base algorithm adopted from JRockit. |
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59 for (unsigned int times = 0; times < loopcount; times++) { |
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60 start = os::elapsed_counter(); |
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61 OrderAccess::fence(); |
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62 fstart = os::rdtsc(); |
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63 |
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64 // use sleep to prevent compiler from optimizing |
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65 os::sleep(Thread::current(), FT_SLEEP_MILLISECS, true); |
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66 |
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67 end = os::elapsed_counter(); |
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68 OrderAccess::fence(); |
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69 fend = os::rdtsc(); |
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70 |
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71 time_base += end - start; |
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72 time_fast += fend - fstart; |
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73 |
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74 // basis for calculating the os tick start |
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75 // to fast time tick start offset |
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76 time_base_elapsed += end; |
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77 time_fast_elapsed += (fend - _epoch); |
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78 } |
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79 |
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80 time_base /= loopcount; |
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81 time_fast /= loopcount; |
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82 time_base_elapsed /= loopcount; |
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83 time_fast_elapsed /= loopcount; |
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84 } |
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85 |
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86 static jlong initialize_frequency() { |
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87 assert(0 == tsc_frequency, "invariant"); |
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88 assert(0 == _epoch, "invariant"); |
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89 const jlong initial_counter = set_epoch(); |
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90 if (initial_counter == 0) { |
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91 return 0; |
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92 } |
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93 // os time frequency |
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94 static double os_freq = (double)os::elapsed_frequency(); |
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95 assert(os_freq > 0, "os_elapsed frequency corruption!"); |
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96 |
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97 double tsc_freq = .0; |
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98 double os_to_tsc_conv_factor = 1.0; |
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99 |
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100 // if platform supports invariant tsc, |
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101 // apply higher resolution and granularity for conversion calculations |
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102 if (VM_Version_Ext::supports_tscinv_ext()) { |
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103 // for invariant tsc platforms, take the maximum qualified cpu frequency |
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104 tsc_freq = (double)VM_Version_Ext::maximum_qualified_cpu_frequency(); |
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105 os_to_tsc_conv_factor = tsc_freq / os_freq; |
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106 } else { |
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107 // use measurements to estimate |
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108 // a conversion factor and the tsc frequency |
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109 |
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110 volatile jlong time_base = 0; |
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111 volatile jlong time_fast = 0; |
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112 volatile jlong time_base_elapsed = 0; |
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113 volatile jlong time_fast_elapsed = 0; |
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114 |
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115 // do measurements to get base data |
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116 // on os timer and fast ticks tsc time relation. |
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117 do_time_measurements(time_base, time_fast, time_base_elapsed, time_fast_elapsed); |
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118 |
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119 // if invalid measurements, cannot proceed |
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120 if (time_fast == 0 || time_base == 0) { |
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121 return 0; |
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122 } |
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123 |
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124 os_to_tsc_conv_factor = (double)time_fast / (double)time_base; |
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125 if (os_to_tsc_conv_factor > 1) { |
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126 // estimate on tsc counter frequency |
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127 tsc_freq = os_to_tsc_conv_factor * os_freq; |
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128 } |
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129 } |
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130 |
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131 if ((tsc_freq < 0) || (tsc_freq > 0 && tsc_freq <= os_freq) || (os_to_tsc_conv_factor <= 1)) { |
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132 // safer to run with normal os time |
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133 tsc_freq = .0; |
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134 } |
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135 |
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136 // frequency of the tsc_counter |
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137 return (jlong)tsc_freq; |
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138 } |
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139 |
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140 static bool initialize_elapsed_counter() { |
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141 tsc_frequency = initialize_frequency(); |
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142 return tsc_frequency != 0 && _epoch != 0; |
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143 } |
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144 |
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145 static bool ergonomics() { |
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146 const bool invtsc_support = Rdtsc::is_supported(); |
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147 if (FLAG_IS_DEFAULT(UseFastUnorderedTimeStamps) && invtsc_support) { |
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148 FLAG_SET_ERGO(bool, UseFastUnorderedTimeStamps, true); |
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149 } |
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150 |
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151 bool ft_enabled = UseFastUnorderedTimeStamps && invtsc_support; |
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152 |
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153 if (!ft_enabled) { |
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154 if (UseFastUnorderedTimeStamps && VM_Version::supports_tsc()) { |
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155 warning("\nThe hardware does not support invariant tsc (INVTSC) register and/or cannot guarantee tsc synchronization between sockets at startup.\n"\ |
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156 "Values returned via rdtsc() are not guaranteed to be accurate, esp. when comparing values from cross sockets reads. Enabling UseFastUnorderedTimeStamps on non-invariant tsc hardware should be considered experimental.\n"); |
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157 ft_enabled = true; |
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158 } |
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159 } |
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160 |
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161 if (!ft_enabled) { |
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162 // Warn if unable to support command-line flag |
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163 if (UseFastUnorderedTimeStamps && !VM_Version::supports_tsc()) { |
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164 warning("Ignoring UseFastUnorderedTimeStamps, hardware does not support normal tsc"); |
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165 } |
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166 } |
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167 |
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168 return ft_enabled; |
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169 } |
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170 |
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171 bool Rdtsc::is_supported() { |
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172 return VM_Version_Ext::supports_tscinv_ext(); |
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173 } |
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174 |
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175 bool Rdtsc::is_elapsed_counter_enabled() { |
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176 return rdtsc_elapsed_counter_enabled; |
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177 } |
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178 |
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179 jlong Rdtsc::frequency() { |
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180 return tsc_frequency; |
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181 } |
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182 |
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183 jlong Rdtsc::elapsed_counter() { |
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184 return os::rdtsc() - _epoch; |
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185 } |
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186 |
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187 jlong Rdtsc::epoch() { |
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188 return _epoch; |
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189 } |
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190 |
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191 jlong Rdtsc::raw() { |
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192 return os::rdtsc(); |
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193 } |
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194 |
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195 bool Rdtsc::initialize() { |
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196 static bool initialized = false; |
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197 if (!initialized) { |
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198 assert(!rdtsc_elapsed_counter_enabled, "invariant"); |
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199 VM_Version_Ext::initialize(); |
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200 assert(0 == tsc_frequency, "invariant"); |
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201 assert(0 == _epoch, "invariant"); |
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202 bool result = initialize_elapsed_counter(); // init hw |
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203 if (result) { |
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204 result = ergonomics(); // check logical state |
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205 } |
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206 rdtsc_elapsed_counter_enabled = result; |
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207 initialized = true; |
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208 } |
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209 return rdtsc_elapsed_counter_enabled; |
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210 } |