/*

 * Copyright (c) 2013, 2019, 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.

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 */

#include "precompiled.hpp"

#include "rdtsc_x86.hpp"

#include "runtime/thread.inline.hpp"

#include "vm_version_ext_x86.hpp"

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

#include OS_CPU_HEADER_INLINE(os)

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

    JavaThread::current()->sleep(FT_SLEEP_MILLISECS);

    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(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;

}