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</ul> </li> <li id="toc-Directory-based" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Directory-based"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Directory-based</span> </div> </a> <ul id="toc-Directory-based-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Coherence_protocols" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Coherence_protocols"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Coherence protocols</span> </div> </a> <ul id="toc-Coherence_protocols-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Further_reading" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Further_reading"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Further reading</span> </div> </a> <ul id="toc-Further_reading-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown 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id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 18 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-18" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">18 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AA%D9%86%D8%B8%D9%8A%D9%85_%D8%A7%D9%84%D9%83%D8%A7%D8%B4_%D9%81%D9%8A_%D8%A7%D9%84%D9%85%D8%B9%D8%A7%D9%84%D8%AC%D8%A7%D8%AA_%D8%A7%D9%84%D8%AA%D9%81%D8%B1%D8%B9%D9%8A%D8%A9" title="تنظيم الكاش في المعالجات التفرعية – Arabic" lang="ar" hreflang="ar" data-title="تنظيم الكاش في المعالجات التفرعية" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Coher%C3%A8ncia_de_la_mem%C3%B2ria_cau" title="Coherència de la memòria cau – Catalan" lang="ca" hreflang="ca" data-title="Coherència de la memòria cau" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Pam%C4%9B%C5%A5ov%C3%A1_koherence" title="Paměťová koherence – Czech" lang="cs" hreflang="cs" data-title="Paměťová koherence" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Cache-Koh%C3%A4renz" title="Cache-Kohärenz – German" lang="de" hreflang="de" data-title="Cache-Kohärenz" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Coherencia_de_cach%C3%A9" title="Coherencia de caché – Spanish" lang="es" hreflang="es" data-title="Coherencia de caché" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%A7%D9%86%D8%B3%D8%AC%D8%A7%D9%85_%D8%AD%D8%A7%D9%81%D8%B8%D9%87_%D9%86%D9%87%D8%A7%D9%86" title="انسجام حافظه نهان – Persian" lang="fa" hreflang="fa" data-title="انسجام حافظه نهان" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Protocole_de_coh%C3%A9rence_de_cache" title="Protocole de cohérence de cache – French" lang="fr" hreflang="fr" data-title="Protocole de cohérence de cache" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%BA%90%EC%8B%9C_%EC%9D%BC%EA%B4%80%EC%84%B1" title="캐시 일관성 – Korean" lang="ko" hreflang="ko" data-title="캐시 일관성" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-it badge-Q70893996 mw-list-item" title=""><a href="https://it.wikipedia.org/wiki/Coerenza_della_cache" title="Coerenza della cache – Italian" lang="it" hreflang="it" data-title="Coerenza della cache" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%82%AD%E3%83%A3%E3%83%83%E3%82%B7%E3%83%A5%E3%82%B3%E3%83%92%E3%83%BC%E3%83%AC%E3%83%B3%E3%82%B7" title="キャッシュコヒーレンシ – Japanese" lang="ja" hreflang="ja" data-title="キャッシュコヒーレンシ" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Protocolos_de_coer%C3%AAncia" title="Protocolos de coerência – Portuguese" lang="pt" hreflang="pt" data-title="Protocolos de coerência" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%9A%D0%BE%D0%B3%D0%B5%D1%80%D0%B5%D0%BD%D1%82%D0%BD%D0%BE%D1%81%D1%82%D1%8C_%D0%BA%D1%8D%D1%88%D0%B0" title="Когерентность кэша – Russian" lang="ru" hreflang="ru" data-title="Когерентность кэша" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Cache_coherence" title="Cache coherence – Simple English" lang="en-simple" hreflang="en-simple" data-title="Cache coherence" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%9A%D0%BE%D1%85%D0%B5%D1%80%D0%B5%D0%BD%D1%82%D0%BD%D0%BE%D1%81%D1%82_%D0%BA%D0%B5%D1%88%D0%B0" title="Кохерентност кеша – Serbian" lang="sr" hreflang="sr" data-title="Кохерентност кеша" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/V%C3%A4limuistin_yhten%C3%A4isyys" title="Välimuistin yhtenäisyys – Finnish" lang="fi" hreflang="fi" data-title="Välimuistin yhtenäisyys" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/%C3%96nbellek_tutarl%C4%B1l%C4%B1%C4%9F%C4%B1" title="Önbellek tutarlılığı – Turkish" lang="tr" hreflang="tr" data-title="Önbellek tutarlılığı" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%9A%D0%BE%D0%B3%D0%B5%D1%80%D0%B5%D0%BD%D1%82%D0%BD%D1%96%D1%81%D1%82%D1%8C_%D0%BA%D0%B5%D1%88%D1%83" title="Когерентність кешу – Ukrainian" lang="uk" hreflang="uk" data-title="Когерентність кешу" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E5%BF%AB%E5%8F%96%E4%B8%80%E8%87%B4%E6%80%A7" title="快取一致性 – Chinese" lang="zh" hreflang="zh" data-title="快取一致性" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q1025017#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> 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searchaux" style="display:none">Equivalence of all cached copies of a memory location</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Cache_coherence.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Cache_coherence.svg/370px-Cache_coherence.svg.png" decoding="async" width="370" height="161" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Cache_coherence.svg/555px-Cache_coherence.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Cache_coherence.svg/740px-Cache_coherence.svg.png 2x" data-file-width="678" data-file-height="295" /></a><figcaption>If two clients have a cached copy of a particular memory block and one client changes the block, the other client's copy must be invalidated or updated. If it is not, the system is in an incoherent state: it contains two different records of the same memory block which both claim to be up-to-date.</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Non_Coherent.gif" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Non_Coherent.gif/220px-Non_Coherent.gif" decoding="async" width="220" height="128" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Non_Coherent.gif/330px-Non_Coherent.gif 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Non_Coherent.gif/440px-Non_Coherent.gif 2x" data-file-width="1200" data-file-height="699" /></a><figcaption>Incoherent caches: The caches have different values of a single address location.</figcaption></figure> <p>In <a href="/wiki/Computer_architecture" title="Computer architecture">computer architecture</a>, <b>cache coherence</b> is the uniformity of shared resource data that is stored in multiple <a href="/wiki/Cache_(computing)" title="Cache (computing)">local caches</a>. In a cache coherent system, if multiple clients have a cached copy of the same region of a shared memory resource, all copies are the same. Without cache coherence, a change made to the region by one client may not be seen by others, and errors can result when the data used by different clients is mismatched.<sup id="cite_ref-advances_in_computers_1-0" class="reference"><a href="#cite_note-advances_in_computers-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p><p>A <a href="/wiki/Cache_coherency_protocols_(examples)" title="Cache coherency protocols (examples)">cache coherence protocol</a> is used to maintain cache coherency. The two main types are <a href="/wiki/Bus_snooping" title="Bus snooping">snooping</a> and <a href="/wiki/Directory-based_cache_coherence" title="Directory-based cache coherence">directory-based</a> protocols. </p><p>Cache coherence is of particular relevance in <a href="/wiki/Multiprocessing" title="Multiprocessing">multiprocessing</a> systems, where each <a href="/wiki/Central_processing_unit" title="Central processing unit">CPU</a> may have its own local cache of a shared memory resource. </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Coherent.gif" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/88/Coherent.gif/220px-Coherent.gif" decoding="async" width="220" height="128" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/88/Coherent.gif/330px-Coherent.gif 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/88/Coherent.gif/440px-Coherent.gif 2x" data-file-width="1200" data-file-height="699" /></a><figcaption>Coherent caches: The value in all the caches' copies is the same.</figcaption></figure> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Overview">Overview</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=1" title="Edit section: Overview"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In a <a href="/wiki/Shared_memory_architecture" class="mw-redirect" title="Shared memory architecture">shared memory</a> multiprocessor system with a separate cache memory for each processor, it is possible to have many copies of shared data: one copy in the main memory and one in the local cache of each processor that requested it. When one of the copies of data is changed, the other copies must reflect that change. Cache coherence is the discipline which ensures that the changes in the values of shared operands (data) are propagated throughout the system in a timely fashion.<sup id="cite_ref-:1_2-0" class="reference"><a href="#cite_note-:1-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p><p>The following are the requirements for cache coherence:<sup id="cite_ref-:0_3-0" class="reference"><a href="#cite_note-:0-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <dl><dt>Write Propagation</dt> <dd>Changes to the data in any cache must be propagated to other copies (of that cache line) in the peer caches.</dd> <dt>Transaction Serialization</dt> <dd>Reads/Writes to a single memory location must be seen by all processors in the same order.</dd></dl> <p>Theoretically, coherence can be performed at the load/store <a href="/wiki/Granularity" title="Granularity">granularity</a>. However, in practice it is generally performed at the granularity of cache blocks.<sup id="cite_ref-:2_4-0" class="reference"><a href="#cite_note-:2-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Definition">Definition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=2" title="Edit section: Definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Coherence defines the behavior of reads and writes to a single address location.<sup id="cite_ref-:0_3-1" class="reference"><a href="#cite_note-:0-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p><p>One type of data occurring simultaneously in different cache memory is called cache coherence, or in some systems, global memory. </p><p>In a multiprocessor system, consider that more than one processor has cached a copy of the memory location X. The following conditions are necessary to achieve cache coherence:<sup id="cite_ref-:3_5-0" class="reference"><a href="#cite_note-:3-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <ol><li>In a read made by a processor P to a location X that follows a write by the same processor P to X, with no writes to X by another processor occurring between the write and the read instructions made by P, X must always return the value written by P.</li> <li>In a read made by a processor P1 to location X that follows a write by another processor P2 to X, with no other writes to X made by any processor occurring between the two accesses and with the read and write being sufficiently separated, X must always return the value written by P2. This condition defines the concept of coherent view of memory. Propagating the writes to the shared memory location ensures that all the caches have a coherent view of the memory. If processor P1 reads the old value of X, even after the write by P2, we can say that the memory is incoherent.</li></ol> <p>The above conditions satisfy the Write Propagation criteria required for cache coherence. However, they are not sufficient as they do not satisfy the Transaction Serialization condition. To illustrate this better, consider the following example: </p><p>A multi-processor system consists of four processors - P1, P2, P3 and P4, all containing cached copies of a shared variable <i>S</i> whose initial value is 0. Processor P1 changes the value of <i>S</i> (in its cached copy) to 10 following which processor P2 changes the value of <i>S</i> in its own cached copy to 20. If we ensure only write propagation, then P3 and P4 will certainly see the changes made to <i>S</i> by P1 and P2. However, P3 may see the change made by P1 after seeing the change made by P2 and hence return 10 on a read to <i>S</i>. P4 on the other hand may see changes made by P1 and P2 in the order in which they are made and hence return 20 on a read to <i>S</i>. The processors P3 and P4 now have an incoherent view of the memory. </p><p>Therefore, in order to satisfy Transaction Serialization, and hence achieve Cache Coherence, the following condition along with the previous two mentioned in this section must be met: </p> <ul><li>Writes to the same location must be sequenced. In other words, if location X received two different values A and B, in this order, from any two processors, the processors can never read location X as B and then read it as A. The location X must be seen with values A and B in that order.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup></li></ul> <p>The alternative definition of a coherent system is via the definition of <a href="/wiki/Sequential_consistency" title="Sequential consistency">sequential consistency</a> memory model: "the cache coherent system must appear to execute all threads’ loads and stores to a <i>single</i> memory location in a total order that respects the program order of each thread".<sup id="cite_ref-:2_4-1" class="reference"><a href="#cite_note-:2-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Thus, the only difference between the cache coherent system and sequentially consistent system is in the number of address locations the definition talks about (single memory location for a cache coherent system, and all memory locations for a sequentially consistent system). </p><p>Another definition is: "a multiprocessor is cache consistent if all writes to the same memory location are performed in some sequential order".<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p><p>Rarely, but especially in algorithms, coherence can instead refer to the <a href="/wiki/Locality_of_reference" title="Locality of reference">locality of reference</a>. Multiple copies of the same data can exist in different cache simultaneously and if processors are allowed to update their own copies freely, an inconsistent view of memory can result. </p> <div class="mw-heading mw-heading2"><h2 id="Coherence_mechanisms">Coherence mechanisms</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=3" title="Edit section: Coherence mechanisms"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Cache_coherency_protocols_(examples)" title="Cache coherency protocols (examples)">Cache coherency protocols (examples)</a></div> <p>The two most common mechanisms of ensuring coherency are <i><a href="/wiki/Bus_sniffing" class="mw-redirect" title="Bus sniffing">snooping</a></i> and <i><a href="/wiki/Directory-based_cache_coherence" title="Directory-based cache coherence">directory-based</a></i>, each having their own benefits and drawbacks.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Snooping based protocols tend to be faster, if enough <a href="/wiki/Memory_bandwidth" title="Memory bandwidth">bandwidth</a> is available, since all transactions are a request/response seen by all processors. The drawback is that snooping isn't scalable. Every request must be broadcast to all nodes in a system, meaning that as the system gets larger, the size of the (logical or physical) bus and the bandwidth it provides must grow. Directories, on the other hand, tend to have longer latencies (with a 3 hop request/forward/respond) but use much less bandwidth since messages are point to point and not broadcast. For this reason, many of the larger systems (>64 processors) use this type of cache coherence. </p> <div class="mw-heading mw-heading3"><h3 id="Snooping">Snooping</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=4" title="Edit section: Snooping"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Bus_snooping" title="Bus snooping">Bus snooping</a></div> <dl><dd>First introduced in 1983,<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> snooping is a process where the individual caches monitor address lines for accesses to memory locations that they have cached.<sup id="cite_ref-:3_5-1" class="reference"><a href="#cite_note-:3-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> The <i>write-invalidate protocols</i> and <i>write-update protocols</i> make use of this mechanism.</dd></dl> <dl><dd>For the snooping mechanism, a snoop filter reduces the snooping traffic by maintaining a plurality of entries, each representing a cache line that may be owned by one or more nodes. When replacement of one of the entries is required, the snoop filter selects for the replacement of the entry representing the cache line or lines owned by the fewest nodes, as determined from a presence vector in each of the entries. A temporal or other type of algorithm is used to refine the selection if more than one cache line is owned by the fewest nodes.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup></dd></dl> <div class="mw-heading mw-heading3"><h3 id="Directory-based">Directory-based</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=5" title="Edit section: Directory-based"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Directory-based_cache_coherence" title="Directory-based cache coherence">Directory-based cache coherence</a></div> <dl><dd>In a directory-based system, the data being shared is placed in a common directory that maintains the coherence between caches. The directory acts as a filter through which the processor must ask permission to load an entry from the primary memory to its cache. When an entry is changed, the directory either updates or invalidates the other caches with that entry.</dd></dl> <p><a href="/wiki/Distributed_shared_memory" title="Distributed shared memory">Distributed shared memory</a> systems mimic these mechanisms in an attempt to maintain consistency between blocks of memory in loosely coupled systems.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Coherence_protocols">Coherence protocols</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=6" title="Edit section: Coherence protocols"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Coherence protocols apply cache coherence in multiprocessor systems. The intention is that two clients must never see different values for the same shared data. </p><p>The protocol must implement the basic requirements for coherence. It can be tailor-made for the target system or application. </p><p>Protocols can also be classified as snoopy or directory-based. Typically, early systems used directory-based protocols where a directory would keep a track of the data being shared and the sharers. In snoopy protocols, the transaction requests (to read, write, or upgrade) are sent out to all processors. All processors snoop the request and respond appropriately. </p><p>Write propagation in snoopy protocols can be implemented by either of the following methods: </p> <dl><dt>Write-invalidate</dt> <dd>When a write operation is observed to a location that a cache has a copy of, the cache controller invalidates its own copy of the snooped memory location, which forces a read from main memory of the new value on its next access.<sup id="cite_ref-:3_5-2" class="reference"><a href="#cite_note-:3-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></dd> <dt>Write-update</dt> <dd>When a write operation is observed to a location that a cache has a copy of, the cache controller updates its own copy of the snooped memory location with the new data.</dd></dl> <p>If the protocol design states that whenever any copy of the shared data is changed, all the other copies must be "updated" to reflect the change, then it is a write-update protocol. If the design states that a write to a cached copy by any processor requires other processors to discard or invalidate their cached copies, then it is a write-invalidate protocol. </p><p>However, scalability is one shortcoming of broadcast protocols. </p><p>Various models and protocols have been devised for maintaining coherence, such as <a href="/wiki/MSI_protocol" title="MSI protocol">MSI</a>, <a href="/wiki/MESI_protocol" title="MESI protocol">MESI</a> (aka Illinois), <a href="/wiki/MOSI_protocol" title="MOSI protocol">MOSI</a>, <a href="/wiki/MOESI_protocol" title="MOESI protocol">MOESI</a>, <a href="/wiki/MERSI_protocol" title="MERSI protocol">MERSI</a>, <a href="/wiki/MESIF_protocol" title="MESIF protocol">MESIF</a>, <a href="/wiki/Write-once_(cache_coherence)" title="Write-once (cache coherence)">write-once</a>, Synapse, Berkeley, <a href="/wiki/Firefly_(cache_coherence_protocol)" title="Firefly (cache coherence protocol)">Firefly</a> and <a href="/wiki/Dragon_protocol" title="Dragon protocol">Dragon protocol</a>.<sup id="cite_ref-:1_2-1" class="reference"><a href="#cite_note-:1-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> In 2011, <a href="/wiki/ARM_Ltd" class="mw-redirect" title="ARM Ltd">ARM Ltd</a> proposed the AMBA 4 ACE<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> for handling coherency in <a href="/wiki/System_on_a_chip" title="System on a chip">SoCs</a>. The AMBA CHI (Coherent Hub Interface) specification<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> from <a href="/wiki/Arm_Ltd." class="mw-redirect" title="Arm Ltd.">ARM Ltd</a>, which belongs to AMBA5 group of specifications defines the interfaces for the connection of fully coherent processors. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=7" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Consistency_model" title="Consistency model">Consistency model</a></li> <li><a href="/wiki/Directory-based_coherence" title="Directory-based coherence">Directory-based coherence</a></li> <li><a href="/wiki/Memory_barrier" title="Memory barrier">Memory barrier</a></li> <li><a href="/wiki/Non-uniform_memory_access" title="Non-uniform memory access">Non-uniform memory access</a> (NUMA)</li> <li><a href="/wiki/False_sharing" title="False sharing">False sharing</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=8" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-advances_in_computers-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-advances_in_computers_1-0">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFMarowka2010" class="citation book cs1">Marowka, Ami (2010-01-01). "Chapter 2 - Pitfalls and Issues of Manycore Programming". <a rel="nofollow" class="external text" href="https://linkinghub.elsevier.com/retrieve/pii/S0065245810790021"><i>Advances in Computers</i></a>. Vol. 79. Elsevier. pp. 71–117. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1016%2Fs0065-2458%2810%2979002-1">10.1016/s0065-2458(10)79002-1</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Chapter+2+-+Pitfalls+and+Issues+of+Manycore+Programming&rft.btitle=Advances+in+Computers&rft.pages=71-117&rft.pub=Elsevier&rft.date=2010-01-01&rft_id=info%3Adoi%2F10.1016%2Fs0065-2458%2810%2979002-1&rft.aulast=Marowka&rft.aufirst=Ami&rft_id=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0065245810790021&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-:1-2"><span class="mw-cite-backlink">^ <a href="#cite_ref-:1_2-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:1_2-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFE._Thomadakis2011" class="citation book cs1">E. Thomadakis, Michael (2011). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20140811023120/http://sc.tamu.edu/systems/eos/nehalem.pdf"><i>The Architecture of the Nehalem Processor and Nehalem-EP SMP Platforms</i></a> <span class="cs1-format">(PDF)</span>. Texas A&M University. p. 30. Archived from <a rel="nofollow" class="external text" href="http://sc.tamu.edu/systems/eos/nehalem.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2014-08-11.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Architecture+of+the+Nehalem+Processor+and+Nehalem-EP+SMP+Platforms&rft.pages=30&rft.pub=Texas+A%26M+University&rft.date=2011&rft.aulast=E.+Thomadakis&rft.aufirst=Michael&rft_id=http%3A%2F%2Fsc.tamu.edu%2Fsystems%2Feos%2Fnehalem.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-:0-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-:0_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:0_3-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFYan" class="citation book cs1">Yan, Solihin. <i>Fundamentals of parallel multicore architecture</i>. <a href="/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/oclc/884540034">884540034</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Fundamentals+of+parallel+multicore+architecture&rft_id=info%3Aoclcnum%2F884540034&rft.aulast=Yan&rft.aufirst=Solihin&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-:2-4"><span class="mw-cite-backlink">^ <a href="#cite_ref-:2_4-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:2_4-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSorin,_Daniel_J.Hill,_Mark_D.Wood,_David_Allen2011" class="citation book cs1">Sorin, Daniel J.; Hill, Mark D.; Wood, David Allen (2011-01-01). <i>A primer on memory consistency and cache coherence</i>. Morgan & Claypool Publishers. <a href="/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/oclc/726930429">726930429</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+primer+on+memory+consistency+and+cache+coherence&rft.pub=Morgan+%26+Claypool+Publishers&rft.date=2011-01-01&rft_id=info%3Aoclcnum%2F726930429&rft.au=Sorin%2C+Daniel+J.&rft.au=Hill%2C+Mark+D.&rft.au=Wood%2C+David+Allen&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-:3-5"><span class="mw-cite-backlink">^ <a href="#cite_ref-:3_5-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:3_5-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-:3_5-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPatterson_and_Hennessy" class="citation book cs1">Patterson and Hennessy. <i>Computer Organization and Design - 4th Edition</i>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-12-374493-7" title="Special:BookSources/978-0-12-374493-7"><bdi>978-0-12-374493-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Computer+Organization+and+Design+-+4th+Edition&rft.isbn=978-0-12-374493-7&rft.au=Patterson+and+Hennessy&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text">Neupane, Mahesh (April 16, 2004). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20100620091706/http://cse.csusb.edu/schubert/tutorials/csci610/w04/MN_Cache_Coherence.pdf">"Cache Coherence"</a> (PDF). Archived from <a rel="nofollow" class="external text" href="http://cse.csusb.edu/schubert/tutorials/csci610/w04/MN_Cache_Coherence.pdf">the original</a> (PDF) on 20 June 2010.</span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSteinkeNutt2004" class="citation journal cs1">Steinke, Robert C.; Nutt, Gary J. (2004-09-01). "A Unified Theory of Shared Memory Consistency". <i>J. ACM</i>. <b>51</b> (5): 800–849. <a href="/wiki/ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/cs/0208027">cs/0208027</a></span>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1145%2F1017460.1017464">10.1145/1017460.1017464</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0004-5411">0004-5411</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:3206071">3206071</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=J.+ACM&rft.atitle=A+Unified+Theory+of+Shared+Memory+Consistency&rft.volume=51&rft.issue=5&rft.pages=800-849&rft.date=2004-09-01&rft_id=info%3Aarxiv%2Fcs%2F0208027&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A3206071%23id-name%3DS2CID&rft.issn=0004-5411&rft_id=info%3Adoi%2F10.1145%2F1017460.1017464&rft.aulast=Steinke&rft.aufirst=Robert+C.&rft.au=Nutt%2C+Gary+J.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPattersonHennessy1990" class="citation book cs1">Patterson, David A.; Hennessy, John L. (1990). <i>Computer Architecture A Quantitative Approach</i>. Morgan Kaufmann Publishers. pp. 467–468. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/1-55860-069-8" title="Special:BookSources/1-55860-069-8"><bdi>1-55860-069-8</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Computer+Architecture+A+Quantitative+Approach&rft.pages=467-468&rft.pub=Morgan+Kaufmann+Publishers&rft.date=1990&rft.isbn=1-55860-069-8&rft.aulast=Patterson&rft.aufirst=David+A.&rft.au=Hennessy%2C+John+L.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation journal cs1"><a rel="nofollow" class="external text" href="http://www.cs.ucr.edu/~ravi/Papers/NWConf/ravishankar_83.pdf">"Ravishankar, Chinya; Goodman, James (February 28, 1983). "Cache Implementation for Multiple Microprocessors"<span class="cs1-kern-right"></span>"</a> <span class="cs1-format">(PDF)</span>. <i>Proceedings of IEEE COMPCON: 346–350</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proceedings+of+IEEE+COMPCON%3A+346%E2%80%93350.&rft.atitle=Ravishankar%2C+Chinya%3B+Goodman%2C+James+%28February+28%2C+1983%29.+%22Cache+Implementation+for+Multiple+Microprocessors%22&rft_id=http%3A%2F%2Fwww.cs.ucr.edu%2F~ravi%2FPapers%2FNWConf%2Fravishankar_83.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text">Rasmus Ulfsnes (June 2013). <a rel="nofollow" class="external text" href="http://www.diva-portal.org/smash/get/diva2:649627/FULLTEXT01.pdf">"Design of a Snoop Filter for Snoop-Based Cache Coherency Protocols"</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20140201160231/http://www.diva-portal.org/smash/get/diva2:649627/FULLTEXT01.pdf">Archived</a> 2014-02-01 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a> (PDF). <i>diva-portal.org</i>. Norwegian University of Science and Technology. Retrieved 2014-01-20.</span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://people.eecs.berkeley.edu/~pattrsn/252F96/Lecture18.pdf">"Lecture 18: Snooping vs. Directory Based Coherency"</a> <span class="cs1-format">(PDF)</span>. <i>Berkeley.edu</i><span class="reference-accessdate">. Retrieved <span class="nowrap">14 May</span> 2023</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Berkeley.edu&rft.atitle=Lecture+18%3A+Snooping+vs.+Directory+Based+Coherency&rft_id=https%3A%2F%2Fpeople.eecs.berkeley.edu%2F~pattrsn%2F252F96%2FLecture18.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKriouile2013" class="citation book cs1">Kriouile (16 September 2013). <i>Formal Analysis of the ACE Specification for Cache Coherent Systems-on-Chip. In Formal Methods for Industrial Critical Systems</i>. Springer Berlin Heidelberg. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-3-642-41010-9" title="Special:BookSources/978-3-642-41010-9"><bdi>978-3-642-41010-9</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Formal+Analysis+of+the+ACE+Specification+for+Cache+Coherent+Systems-on-Chip.+In+Formal+Methods+for+Industrial+Critical+Systems&rft.pub=Springer+Berlin+Heidelberg&rft.date=2013-09-16&rft.isbn=978-3-642-41010-9&rft.au=Kriouile&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> <li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLtd" class="citation web cs1">Ltd, Arm. <a rel="nofollow" class="external text" href="https://developer.arm.com/architectures/system-architectures/amba/amba-5">"AMBA | AMBA 5"</a>. <i>Arm Developer</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2021-04-27</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Arm+Developer&rft.atitle=AMBA+%7C+AMBA+5&rft.aulast=Ltd&rft.aufirst=Arm&rft_id=https%3A%2F%2Fdeveloper.arm.com%2Farchitectures%2Fsystem-architectures%2Famba%2Famba-5&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></span> </li> </ol></div> <div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cache_coherence&action=edit&section=9" title="Edit section: Further reading"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPattersonHennessy2009" class="citation book cs1"><a href="/wiki/David_Patterson_(scientist)" class="mw-redirect" title="David Patterson (scientist)">Patterson, David</a>; <a href="/wiki/John_L._Hennessy" title="John L. Hennessy">Hennessy, John</a> (2009). <i>Computer Organization and Design</i> (4th ed.). <a href="/wiki/Morgan_Kaufmann" class="mw-redirect" title="Morgan Kaufmann">Morgan Kaufmann</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-12-374493-7" title="Special:BookSources/978-0-12-374493-7"><bdi>978-0-12-374493-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Computer+Organization+and+Design&rft.edition=4th&rft.pub=Morgan+Kaufmann&rft.date=2009&rft.isbn=978-0-12-374493-7&rft.aulast=Patterson&rft.aufirst=David&rft.au=Hennessy%2C+John&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFHandy1998" class="citation book cs1">Handy, Jim (1998). <i>The Cache Memory Book</i> (2nd ed.). <a href="/wiki/Morgan_Kaufmann" class="mw-redirect" title="Morgan Kaufmann">Morgan Kaufmann</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9780123229809" title="Special:BookSources/9780123229809"><bdi>9780123229809</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Cache+Memory+Book&rft.edition=2nd&rft.pub=Morgan+Kaufmann&rft.date=1998&rft.isbn=9780123229809&rft.aulast=Handy&rft.aufirst=Jim&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSorinHillWood2011" class="citation book cs1">Sorin, Daniel; Hill, Mark; Wood, David (2011). <a rel="nofollow" class="external text" href="https://www.ece.cmu.edu/~ece847c/S15/lib/exe/fetch.php?media=part2_2_sorin12.pdf"><i>A Primer on Memory Consistency and Cache Coherence</i></a> <span class="cs1-format">(PDF)</span>. <a href="/w/index.php?title=Morgan_and_Claypool&action=edit&redlink=1" class="new" title="Morgan and Claypool (page does not exist)">Morgan and Claypool</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1608455645" title="Special:BookSources/978-1608455645"><bdi>978-1608455645</bdi></a><span class="reference-accessdate">. Retrieved <span class="nowrap">20 October</span> 2017</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+Primer+on+Memory+Consistency+and+Cache+Coherence&rft.pub=Morgan+and+Claypool&rft.date=2011&rft.isbn=978-1608455645&rft.aulast=Sorin&rft.aufirst=Daniel&rft.au=Hill%2C+Mark&rft.au=Wood%2C+David&rft_id=https%3A%2F%2Fwww.ece.cmu.edu%2F~ece847c%2FS15%2Flib%2Fexe%2Ffetch.php%3Fmedia%3Dpart2_2_sorin12.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSteinkeNutt2004" class="citation journal cs1">Steinke, Robert C.; Nutt, Gary J. (1 September 2004). "A unified theory of shared memory consistency". <i>Journal of the ACM</i>. <b>51</b> (5): 800–849. <a href="/wiki/ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/cs/0208027">cs/0208027</a></span>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1145%2F1017460.1017464">10.1145/1017460.1017464</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:3206071">3206071</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Journal+of+the+ACM&rft.atitle=A+unified+theory+of+shared+memory+consistency&rft.volume=51&rft.issue=5&rft.pages=800-849&rft.date=2004-09-01&rft_id=info%3Aarxiv%2Fcs%2F0208027&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A3206071%23id-name%3DS2CID&rft_id=info%3Adoi%2F10.1145%2F1017460.1017464&rft.aulast=Steinke&rft.aufirst=Robert+C.&rft.au=Nutt%2C+Gary+J.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACache+coherence" class="Z3988"></span></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline 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template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Parallel_computing" title="Template talk:Parallel computing"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Parallel_computing" title="Special:EditPage/Template:Parallel computing"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Parallel_computing" style="font-size:114%;margin:0 4em"><a href="/wiki/Parallel_computing" title="Parallel computing">Parallel computing</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">General</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Distributed_computing" title="Distributed computing">Distributed computing</a></li> <li><a href="/wiki/Parallel_computing" title="Parallel computing">Parallel computing</a></li> <li><a href="/wiki/Massively_parallel" title="Massively parallel">Massively parallel</a></li> <li><a href="/wiki/Cloud_computing" title="Cloud computing">Cloud computing</a></li> <li><a href="/wiki/High-performance_computing" title="High-performance computing">High-performance computing</a></li> <li><a href="/wiki/Multiprocessing" title="Multiprocessing">Multiprocessing</a></li> <li><a href="/wiki/Manycore_processor" title="Manycore processor">Manycore processor</a></li> <li><a href="/wiki/General-purpose_computing_on_graphics_processing_units" title="General-purpose computing on graphics processing units">GPGPU</a></li> <li><a href="/wiki/Computer_network" title="Computer network">Computer network</a></li> <li><a href="/wiki/Systolic_array" title="Systolic array">Systolic array</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Levels</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Bit-level_parallelism" title="Bit-level parallelism">Bit</a></li> <li><a href="/wiki/Instruction-level_parallelism" title="Instruction-level parallelism">Instruction</a></li> <li><a href="/wiki/Task_parallelism" title="Task parallelism">Thread</a></li> <li><a href="/wiki/Task_parallelism" title="Task parallelism">Task</a></li> <li><a href="/wiki/Data_parallelism" title="Data parallelism">Data</a></li> <li><a href="/wiki/Memory-level_parallelism" title="Memory-level parallelism">Memory</a></li> <li><a href="/wiki/Loop-level_parallelism" title="Loop-level parallelism">Loop</a></li> <li><a href="/wiki/Pipeline_(computing)" title="Pipeline (computing)">Pipeline</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Multithreading_(computer_architecture)" title="Multithreading (computer architecture)">Multithreading</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Temporal_multithreading" title="Temporal multithreading">Temporal</a></li> <li><a href="/wiki/Simultaneous_multithreading" title="Simultaneous multithreading">Simultaneous</a> (SMT)</li> <li><a href="/wiki/Simultaneous_and_heterogeneous_multithreading" title="Simultaneous and heterogeneous multithreading">Simultaneous and heterogenous</a></li> <li><a href="/wiki/Speculative_multithreading" title="Speculative multithreading">Speculative</a> (SpMT)</li> <li><a href="/wiki/Preemption_(computing)" title="Preemption (computing)">Preemptive</a></li> <li><a href="/wiki/Computer_multitasking#Cooperative_multitasking" title="Computer multitasking">Cooperative</a></li> <li><a href="/wiki/Bulldozer_(microarchitecture)#Bulldozer_core" title="Bulldozer (microarchitecture)">Clustered multi-thread</a> (CMT)</li> <li><a href="/wiki/Hardware_scout" title="Hardware scout">Hardware scout</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Theory</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Parallel_RAM" title="Parallel RAM">PRAM model</a></li> <li><a href="/wiki/Parallel_external_memory" title="Parallel external memory">PEM model</a></li> <li><a href="/wiki/Analysis_of_parallel_algorithms" title="Analysis of parallel algorithms">Analysis of parallel algorithms</a></li> <li><a href="/wiki/Amdahl%27s_law" title="Amdahl's law">Amdahl's law</a></li> <li><a href="/wiki/Gustafson%27s_law" title="Gustafson's law">Gustafson's law</a></li> <li><a href="/wiki/Cost_efficiency" title="Cost efficiency">Cost efficiency</a></li> <li><a href="/wiki/Karp%E2%80%93Flatt_metric" title="Karp–Flatt metric">Karp–Flatt metric</a></li> <li><a href="/wiki/Parallel_slowdown" title="Parallel slowdown">Slowdown</a></li> <li><a href="/wiki/Speedup" title="Speedup">Speedup</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Elements</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Process_(computing)" title="Process (computing)">Process</a></li> <li><a href="/wiki/Thread_(computing)" title="Thread (computing)">Thread</a></li> <li><a href="/wiki/Fiber_(computer_science)" title="Fiber (computer science)">Fiber</a></li> <li><a href="/wiki/Instruction_window" title="Instruction window">Instruction window</a></li> <li><a href="/wiki/Array_(data_structure)" title="Array (data structure)">Array</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Coordination</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Multiprocessing" title="Multiprocessing">Multiprocessing</a></li> <li><a href="/wiki/Memory_coherence" title="Memory coherence">Memory coherence</a></li> <li><a class="mw-selflink selflink">Cache coherence</a></li> <li><a href="/wiki/Cache_invalidation" title="Cache invalidation">Cache invalidation</a></li> <li><a href="/wiki/Barrier_(computer_science)" title="Barrier (computer science)">Barrier</a></li> <li><a href="/wiki/Synchronization_(computer_science)" title="Synchronization (computer science)">Synchronization</a></li> <li><a href="/wiki/Application_checkpointing" title="Application checkpointing">Application checkpointing</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Computer_programming" title="Computer programming">Programming</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Stream_processing" title="Stream processing">Stream processing</a></li> <li><a href="/wiki/Dataflow_programming" title="Dataflow programming">Dataflow programming</a></li> <li><a href="/wiki/Parallel_programming_model" title="Parallel programming model">Models</a> <ul><li><a href="/wiki/Implicit_parallelism" title="Implicit parallelism">Implicit parallelism</a></li> <li><a href="/wiki/Explicit_parallelism" title="Explicit parallelism">Explicit parallelism</a></li> <li><a href="/wiki/Concurrency_(computer_science)" title="Concurrency (computer science)">Concurrency</a></li></ul></li> <li><a href="/wiki/Non-blocking_algorithm" title="Non-blocking algorithm">Non-blocking algorithm</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Computer_hardware" title="Computer hardware">Hardware</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Flynn%27s_taxonomy" title="Flynn's taxonomy">Flynn's taxonomy</a> <ul><li><a href="/wiki/Single_instruction,_single_data" title="Single instruction, single data">SISD</a></li> <li><a href="/wiki/Single_instruction,_multiple_data" title="Single instruction, multiple data">SIMD</a> <ul><li><a href="/wiki/Single_instruction,_multiple_threads" title="Single instruction, multiple threads">Array processing</a> (SIMT)</li> <li><a href="/wiki/Flynn%27s_taxonomy#Pipelined_processor" title="Flynn's taxonomy">Pipelined processing</a></li> <li><a href="/wiki/Flynn%27s_taxonomy#Associative_processor" title="Flynn's taxonomy">Associative processing</a></li></ul></li> <li><a href="/wiki/Multiple_instruction,_single_data" title="Multiple instruction, single data">MISD</a></li> <li><a href="/wiki/Multiple_instruction,_multiple_data" title="Multiple instruction, multiple data">MIMD</a></li></ul></li> <li><a href="/wiki/Dataflow_architecture" title="Dataflow architecture">Dataflow architecture</a></li> <li><a href="/wiki/Instruction_pipelining" title="Instruction pipelining">Pipelined processor</a></li> <li><a href="/wiki/Superscalar_processor" title="Superscalar processor">Superscalar processor</a></li> <li><a href="/wiki/Vector_processor" title="Vector processor">Vector processor</a></li> <li><a href="/wiki/Multiprocessing" title="Multiprocessing">Multiprocessor</a> <ul><li><a href="/wiki/Symmetric_multiprocessing" title="Symmetric multiprocessing">symmetric</a></li> <li><a href="/wiki/Asymmetric_multiprocessing" title="Asymmetric multiprocessing">asymmetric</a></li></ul></li> <li><a href="/wiki/Semiconductor_memory" title="Semiconductor memory">Memory</a> <ul><li><a href="/wiki/Shared_memory" title="Shared memory">shared</a></li> <li><a href="/wiki/Distributed_memory" title="Distributed memory">distributed</a></li> <li><a href="/wiki/Distributed_shared_memory" title="Distributed shared memory">distributed shared</a></li> <li><a href="/wiki/Uniform_memory_access" title="Uniform memory access">UMA</a></li> <li><a href="/wiki/Non-uniform_memory_access" title="Non-uniform memory access">NUMA</a></li> <li><a href="/wiki/Cache-only_memory_architecture" title="Cache-only memory architecture">COMA</a></li></ul></li> <li><a href="/wiki/Massively_parallel" title="Massively parallel">Massively parallel</a> computer</li> <li><a href="/wiki/Computer_cluster" title="Computer cluster">Computer cluster</a> <ul><li><a href="/wiki/Beowulf_cluster" title="Beowulf cluster">Beowulf cluster</a></li></ul></li> <li><a href="/wiki/Grid_computing" title="Grid computing">Grid computer</a></li> <li><a href="/wiki/Hardware_acceleration" title="Hardware acceleration">Hardware acceleration</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/API" title="API">APIs</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ateji_PX" title="Ateji PX">Ateji PX</a></li> <li><a href="/wiki/Boost_(C%2B%2B_libraries)" title="Boost (C++ libraries)">Boost</a></li> <li><a href="/wiki/Chapel_(programming_language)" title="Chapel (programming language)">Chapel</a></li> <li><a href="/wiki/HPX" title="HPX">HPX</a></li> <li><a href="/wiki/Charm%2B%2B" title="Charm++">Charm++</a></li> <li><a href="/wiki/Cilk" title="Cilk">Cilk</a></li> <li><a href="/wiki/Coarray_Fortran" title="Coarray Fortran">Coarray Fortran</a></li> <li><a href="/wiki/CUDA" title="CUDA">CUDA</a></li> <li><a href="/wiki/Dryad_(programming)" title="Dryad (programming)">Dryad</a></li> <li><a href="/wiki/C%2B%2B_AMP" title="C++ AMP">C++ AMP</a></li> <li><a href="/wiki/Global_Arrays" title="Global Arrays">Global Arrays</a></li> <li><a href="/wiki/GPUOpen" title="GPUOpen">GPUOpen</a></li> <li><a href="/wiki/Message_Passing_Interface" title="Message Passing Interface">MPI</a></li> <li><a href="/wiki/OpenMP" title="OpenMP">OpenMP</a></li> <li><a href="/wiki/OpenCL" title="OpenCL">OpenCL</a></li> <li><a href="/wiki/OpenHMPP" title="OpenHMPP">OpenHMPP</a></li> <li><a href="/wiki/OpenACC" title="OpenACC">OpenACC</a></li> <li><a href="/wiki/Parallel_Extensions" title="Parallel Extensions">Parallel Extensions</a></li> <li><a href="/wiki/Parallel_Virtual_Machine" title="Parallel Virtual Machine">PVM</a></li> <li><a href="/wiki/Pthreads" title="Pthreads">pthreads</a></li> <li><a href="/wiki/RaftLib" title="RaftLib">RaftLib</a></li> <li><a href="/wiki/ROCm" title="ROCm">ROCm</a></li> <li><a href="/wiki/Unified_Parallel_C" title="Unified Parallel C">UPC</a></li> <li><a href="/wiki/Threading_Building_Blocks" title="Threading Building Blocks">TBB</a></li> <li><a href="/wiki/ZPL_(programming_language)" class="mw-redirect" title="ZPL (programming language)">ZPL</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Problems</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Automatic_parallelization" title="Automatic parallelization">Automatic parallelization</a></li> <li><a href="/wiki/Deadlock_(computer_science)" title="Deadlock (computer science)">Deadlock</a></li> <li><a href="/wiki/Deterministic_algorithm" title="Deterministic algorithm">Deterministic algorithm</a></li> <li><a href="/wiki/Embarrassingly_parallel" title="Embarrassingly parallel">Embarrassingly parallel</a></li> <li><a href="/wiki/Parallel_slowdown" title="Parallel slowdown">Parallel slowdown</a></li> <li><a href="/wiki/Race_condition" title="Race condition">Race condition</a></li> <li><a href="/wiki/Software_lockout" title="Software lockout">Software lockout</a></li> <li><a href="/wiki/Scalability" title="Scalability">Scalability</a></li> <li><a href="/wiki/Starvation_(computer_science)" title="Starvation (computer science)">Starvation</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" 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