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 /*

  * Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 //#include "os_linux_x86.inline.hpp"

 #ifdef TARGET_OS_ARCH_linux_x86

 # include "os_linux_x86.inline.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_bsd_x86

 # include "os_bsd_x86.inline.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_windows_x86

 # include "os_windows_x86.inline.hpp"

 #endif

 #ifdef TARGET_OS_ARCH_solaris_x86

 # include "os_solaris_x86.inline.hpp"

 #endif

 #include "rdtsc_x86.hpp"

 #include "runtime/thread.inline.hpp"

 #include "vm_version_ext_x86.hpp"

 #include "runtime/os.hpp"

 // The following header contains the implementations of rdtsc()

 static jlong _epoch = 0;

 static bool rdtsc_elapsed_counter_enabled = false;

 static jlong tsc_frequency = 0;

 static jlong set_epoch() {

   assert(0 == _epoch, "invariant");

   _epoch = os::rdtsc();

   return _epoch;

 }

 // Base loop to estimate ticks frequency for tsc counter from user mode.

 // Volatiles and sleep() are used to prevent compiler from applying optimizations.

 static void do_time_measurements(volatile jlong& time_base,

                                  volatile jlong& time_fast,

                                  volatile jlong& time_base_elapsed,

                                  volatile jlong& time_fast_elapsed) {

   static const unsigned int FT_SLEEP_MILLISECS = 1;

   const unsigned int loopcount = 3;

   volatile jlong start = 0;

   volatile jlong fstart = 0;

   volatile jlong end = 0;

   volatile jlong fend = 0;

   // Figure out the difference between rdtsc and os provided timer.

   // base algorithm adopted from JRockit.

   for (unsigned int times = 0; times < loopcount; times++) {

     start = os::elapsed_counter();

     OrderAccess::fence();

     fstart = os::rdtsc();

     // use sleep to prevent compiler from optimizing

     os::sleep(Thread::current(), FT_SLEEP_MILLISECS, true);

     end = os::elapsed_counter();

     OrderAccess::fence();

     fend = os::rdtsc();

     time_base += end - start;

     time_fast += fend - fstart;

     // basis for calculating the os tick start

     // to fast time tick start offset

     time_base_elapsed += end;

     time_fast_elapsed += (fend - _epoch);

   }

   time_base /= loopcount;

   time_fast /= loopcount;

   time_base_elapsed /= loopcount;

   time_fast_elapsed /= loopcount;

 }

 static jlong initialize_frequency() {

   assert(0 == tsc_frequency, "invariant");

   assert(0 == _epoch, "invariant");

   const jlong initial_counter = set_epoch();

   if (initial_counter == 0) {

     return 0;

   }

   // os time frequency

   static double os_freq = (double)os::elapsed_frequency();

   assert(os_freq > 0, "os_elapsed frequency corruption!");

   double tsc_freq = .0;

   double os_to_tsc_conv_factor = 1.0;

   // if platform supports invariant tsc,

   // apply higher resolution and granularity for conversion calculations

   if (VM_Version_Ext::supports_tscinv_ext()) {

     // for invariant tsc platforms, take the maximum qualified cpu frequency

     tsc_freq = (double)VM_Version_Ext::maximum_qualified_cpu_frequency();

     os_to_tsc_conv_factor = tsc_freq / os_freq;

   } else {

     // use measurements to estimate

     // a conversion factor and the tsc frequency

     volatile jlong time_base = 0;

     volatile jlong time_fast = 0;

     volatile jlong time_base_elapsed = 0;

     volatile jlong time_fast_elapsed = 0;

     // do measurements to get base data

     // on os timer and fast ticks tsc time relation.

     do_time_measurements(time_base, time_fast, time_base_elapsed, time_fast_elapsed);

     // if invalid measurements, cannot proceed

     if (time_fast == 0 || time_base == 0) {

       return 0;

     }

     os_to_tsc_conv_factor = (double)time_fast / (double)time_base;

     if (os_to_tsc_conv_factor > 1) {

       // estimate on tsc counter frequency

       tsc_freq = os_to_tsc_conv_factor * os_freq;

     }

   }

   if ((tsc_freq < 0) || (tsc_freq > 0 && tsc_freq <= os_freq) || (os_to_tsc_conv_factor <= 1)) {

     // safer to run with normal os time

     tsc_freq = .0;

   }

   // frequency of the tsc_counter

   return (jlong)tsc_freq;

 }

 static bool initialize_elapsed_counter() {

   tsc_frequency = initialize_frequency();

   return tsc_frequency != 0 && _epoch != 0;

 }

 static bool ergonomics() {

   const bool invtsc_support = Rdtsc::is_supported();

   if (FLAG_IS_DEFAULT(UseFastUnorderedTimeStamps) && invtsc_support) {

     FLAG_SET_ERGO(bool, UseFastUnorderedTimeStamps, true);

   }

   bool ft_enabled = UseFastUnorderedTimeStamps && invtsc_support;

   if (!ft_enabled) {

     if (UseFastUnorderedTimeStamps && VM_Version::supports_tsc()) {

       warning("\nThe hardware does not support invariant tsc (INVTSC) register and/or cannot guarantee tsc synchronization between sockets at startup.\n"\

         "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");

       ft_enabled = true;

     }

   }

   if (!ft_enabled) {

     // Warn if unable to support command-line flag

     if (UseFastUnorderedTimeStamps && !VM_Version::supports_tsc()) {

       warning("Ignoring UseFastUnorderedTimeStamps, hardware does not support normal tsc");

     }

   }

   return ft_enabled;

 }

 bool Rdtsc::is_supported() {

   return VM_Version_Ext::supports_tscinv_ext();

 }

 bool Rdtsc::is_elapsed_counter_enabled() {

   return rdtsc_elapsed_counter_enabled;

 }

 jlong Rdtsc::frequency() {

   return tsc_frequency;

 }

 jlong Rdtsc::elapsed_counter() {

   return os::rdtsc() - _epoch;

 }

 jlong Rdtsc::epoch() {

   return _epoch;

 }

 jlong Rdtsc::raw() {

   return os::rdtsc();

 }

 bool Rdtsc::initialize() {

   static bool initialized = false;

   if (!initialized) {

     assert(!rdtsc_elapsed_counter_enabled, "invariant");

     VM_Version_Ext::initialize();

     assert(0 == tsc_frequency, "invariant");

     assert(0 == _epoch, "invariant");

     bool result = initialize_elapsed_counter(); // init hw

     if (result) {

       result = ergonomics(); // check logical state

     }

     rdtsc_elapsed_counter_enabled = result;

     initialized = true;

   }

   return rdtsc_elapsed_counter_enabled;

 }