1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Specualtive execution</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Fiber"> 8<link rel="up" href="../index.html" title="Chapter 1. Fiber"> 9<link rel="prev" href="integration/deeper_dive_into___boost_asio__.html" title="Deeper Dive into Boost.Asio"> 10<link rel="next" href="numa.html" title="NUMA"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="integration/deeper_dive_into___boost_asio__.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="numa.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="fiber.speculation"></a><a name="speculation"></a><a class="link" href="speculation.html" title="Specualtive execution">Specualtive 28 execution</a> 29</h2></div></div></div> 30<h4> 31<a name="fiber.speculation.h0"></a> 32 <span class="phrase"><a name="fiber.speculation.hardware_transactional_memory"></a></span><a class="link" href="speculation.html#fiber.speculation.hardware_transactional_memory">Hardware 33 transactional memory</a> 34 </h4> 35<p> 36 With help of hardware transactional memory multiple logical processors execute 37 a critical region speculatively, e.g. without explicit synchronization.<br> 38 If the transactional execution completes successfully, then all memory operations 39 performed within the transactional region are commited without any inter-thread 40 serialization.<br> When the optimistic execution fails, the processor aborts 41 the transaction and discards all performed modifications.<br> In non-transactional 42 code a single lock serializes the access to a critical region. With a transactional 43 memory, multiple logical processor start a transaction and update the memory 44 (the data) inside the ciritical region. Unless some logical processors try 45 to update the same data, the transactions would always succeed. 46 </p> 47<h4> 48<a name="fiber.speculation.h1"></a> 49 <span class="phrase"><a name="fiber.speculation.intel_transactional_synchronisation_extensions__tsx_"></a></span><a class="link" href="speculation.html#fiber.speculation.intel_transactional_synchronisation_extensions__tsx_">Intel 50 Transactional Synchronisation Extensions (TSX)</a> 51 </h4> 52<p> 53 TSX is Intel's implementation of hardware transactional memory in modern Intel 54 processors<a href="#ftn.fiber.speculation.f0" class="footnote" name="fiber.speculation.f0"><sup class="footnote">[7]</sup></a>.<br> In TSX the hardware keeps track of which cachelines have 55 been read from and which have been written to in a transaction. The cache-line 56 size (64-byte) and the n-way set associative cache determine the maximum size 57 of memory in a transaction. For instance if a transaction modifies 9 cache-lines 58 at a processor with a 8-way set associative cache, the transaction will always 59 be aborted. 60 </p> 61<div class="note"><table border="0" summary="Note"> 62<tr> 63<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> 64<th align="left">Note</th> 65</tr> 66<tr><td align="left" valign="top"><p> 67 TXS is enabled if property <code class="computeroutput"><span class="identifier">htm</span><span class="special">=</span><span class="identifier">tsx</span></code> is 68 specified at b2 command-line and <code class="computeroutput"><span class="identifier">BOOST_USE_TSX</span></code> 69 is applied to the compiler. 70 </p></td></tr> 71</table></div> 72<div class="note"><table border="0" summary="Note"> 73<tr> 74<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> 75<th align="left">Note</th> 76</tr> 77<tr><td align="left" valign="top"><p> 78 A TSX-transaction will be aborted if the floating point state is modified 79 inside a critical region. As a consequence floating point operations, e.g. 80 store/load of floating point related registers during a fiber (context) switch 81 are disabled. 82 </p></td></tr> 83</table></div> 84<div class="important"><table border="0" summary="Important"> 85<tr> 86<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../../doc/src/images/important.png"></td> 87<th align="left">Important</th> 88</tr> 89<tr><td align="left" valign="top"><p> 90 TSX can not be used together with MSVC at this time! 91 </p></td></tr> 92</table></div> 93<p> 94 Boost.Fiber uses TSX-enabled spinlocks to protect critical regions (see section 95 <a class="link" href="tuning.html#tuning">Tuning</a>). 96 </p> 97<div class="footnotes"> 98<br><hr style="width:100; text-align:left;margin-left: 0"> 99<div id="ftn.fiber.speculation.f0" class="footnote"><p><a href="#fiber.speculation.f0" class="para"><sup class="para">[7] </sup></a> 100 intel.com: <a href="https://software.intel.com/en-us/node/695149" target="_top">Intel 101 Transactional Synchronization Extensions</a> 102 </p></div> 103</div> 104</div> 105<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 106<td align="left"></td> 107<td align="right"><div class="copyright-footer">Copyright © 2013 Oliver Kowalke<p> 108 Distributed under the Boost Software License, Version 1.0. (See accompanying 109 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 110 </p> 111</div></td> 112</tr></table> 113<hr> 114<div class="spirit-nav"> 115<a accesskey="p" href="integration/deeper_dive_into___boost_asio__.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="numa.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 116</div> 117</body> 118</html> 119
