| /* |
| * 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 "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 |
| 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; |
| } |