Editing Hyper-threading (section)

== Drawbacks ==
{{Anchor|Drawback}}
When the first HT processors were released, many operating systems were not optimized for hyper-threading technology (e.g. Windows 2000 and Linux older than 2.4).<ref>{{cite web|url=http://www.intel.com/support/processors/pentium4/sb/cs-017371.htm#1c|title=Hyper-Threading Technology – Operating systems that include optimizations for Hyper-Threading Technology |publisher=Intel.com |date=2011-09-19 |access-date=2012-02-29}}</ref>

In 2006, hyper-threading was criticised for energy inefficiency.<ref>{{cite book|title=Sustainable Practices: Concepts, Methodologies, Tools and Applications|isbn=9781466648524|page=666|publisher=Information Resources Management Association|date=December 2013}}</ref> For example, [[ARM Holdings|ARM]] (a specialized, low-power, CPU design company), stated that simultaneous multithreading can use up to 46% more power than ordinary dual-core designs. Furthermore, they claimed that SMT increases [[cache thrashing]] by 42%, whereas [[dual core]] results in a 37% decrease.<ref>{{cite web|url=http://www.theinquirer.net/inquirer/news/1037948/arm-fan-hyperthreading |archive-url=https://web.archive.org/web/20090906005322/http://www.theinquirer.net/inquirer/news/1037948/arm-fan-hyperthreading |url-status=unfit |archive-date=6 September 2009 |title=ARM is no fan of HyperThreading |publisher=theinquirer.net |date=2006-08-02 |access-date=2012-02-29}}</ref>

In 2010, ARM said it might include simultaneous multithreading in its future chips;<ref>{{cite web|first=Tom|last=Jermoluk |url=http://www.top500.org/blog/2010/10/13/about_mips_and_mips |title=About MIPS and MIPS &#124; TOP500 Supercomputing Sites |website=Top500.org |date=2010-10-13 |access-date=2011-04-05 |url-status=dead |archive-url=https://web.archive.org/web/20110613203023/http://www.top500.org/blog/2010/10/13/about_mips_and_mips |archive-date=13 June 2011}}</ref> however, this was rejected in favor of their 2012 64-bit design.<ref>{{cite web|url=http://www.techdesignforums.com/blog/2012/10/30/arm-64bit-cortex-a53-a57-launch/|title=ARM launches first 64bit processor core for servers and smartphones|date=30 October 2012|website=Tech Design Forum}}</ref> ARM produced SMT cores in 2018.<ref>{{Cite web |title=Arm launches first SMT-capable Cortex core {{!}} bit-tech.net |url=https://bit-tech.net/news/arm-launches-first-smt-capable-cortex-core/1/ |access-date=2023-12-02 |website=bit-tech.net |language=en}}</ref>

In 2013, Intel dropped SMT in favor of [[out-of-order execution]] for its [[Silvermont]] processor cores, as they found this gave better performance with better power efficiency than a lower number of cores with SMT.<ref>{{Cite news |title= Deep inside Intel's first viable mobile processor: Silvermont |author=  Rik Myslewski |work= The Register |date= 8 May 2013 |url=  https://www.theregister.co.uk/2013/05/08/intel_silvermont_microarchitecture/ |access-date= 13 January 2014 }}</ref>

In 2017, it was revealed that Intel's [[Skylake (microarchitecture)|Skylake]] and [[Kaby Lake]] processors had a bug in their implementation of hyper-threading that could cause data loss.<ref>{{Cite news|url=https://www.theregister.co.uk/2017/06/25/intel_skylake_kaby_lake_hyperthreading/|title=Intel's Skylake and Kaby Lake CPUs have nasty hyper-threading bug|first=Richard|last=Chirgwin|date=25 June 2017|access-date=4 July 2017|work=The Register}}</ref> [[Microcode]] updates were later released to address the issue.<ref name="htbugars">{{cite news|url=https://arstechnica.com/information-technology/2017/06/skylake-kaby-lake-chips-have-a-crash-bug-with-hyperthreading-enabled/|title=Skylake, Kaby Lake Chips Have a Crash Bug with Hyperthreading Enabled|work=[[Ars Technica]]|access-date=25 November 2017|date=26 June 2017}}</ref>

In 2019, with [[Coffee Lake]], Intel temporarily moved away from including hyper-threading in mainstream Core i7 desktop processors except for highest-end Core i9 parts or Pentium Gold CPUs.<ref>{{cite news|url=https://www.anandtech.com/show/14256/intel-9th-gen-core-processors-all-the-desktop-and-mobile-45w-cpus-announced|title=Intel 9th Gen Core Processors: All the Desktop and Mobile 45W CPUs Announced|first=Ian|last=Cutress|date=23 April 2019|work=AnandTech}}</ref> It also began to recommend disabling hyper-threading, as [[Spectre (security vulnerability)|new CPU vulnerability]] attacks were revealed which could be mitigated by disabling HT.<ref>
{{cite news
 |url=https://www.tomshardware.co.uk/intel-disable-hyper-threading-spectre-attack,news-60647.html
 |title=Intel's New Spectre-Like Flaw Affects Chips Made Since 2008
 |first=Lucian|last=Armasu
 |date=14 May 2019
 |url-status=dead
 |archive-url=https://web.archive.org/web/20190804172710/https://www.tomshardware.co.uk/intel-disable-hyper-threading-spectre-attack,news-60647.html
 |archive-date=4 August 2019
 |work=[[Tom's Hardware]]}}</ref>