Hyper-threading and its drawbacks

Hyper-threading(officially Hyper-Threading Technology or HT Technology, abbreviated HTT or HT)
For each processor core that is physically present, the operating system addresses two virtual or logical cores, and shares the workload between them when possible. The main function of hyper-threading is to decrease the number of dependent instructions on the pipeline. It takes advantage of superscalar architecture (multiple instructions operating on separate data in parallel). They appear to the OS as two processors, thus the OS can schedule two processes at once. In addition two or more processes can use the same resources. If one process fails then the resources can be readily re-allocated.

Hyper-threading requires not only that the operating system supports SMT, but also that it be specifically optimized for HTT, and Intel recommends disabling HTT when using operating systems that have not been optimized for this chip feature.


Drawbacks
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).
In 2006, hyper-threading was criticised for energy inefficiency. For example, specialist low-power CPU design company ARM stated simultaneous multithreading (SMT) can use up to 46% more power than ordinary dual-core designs. Furthermore, they claimed SMT increases cache thrashing by 42%, whereas dual core results in a 37% decrease.  Intel disputed this claim, stating that hyper-threading is highly efficient because it uses resources that would otherwise be idle.
In 2010, ARM said it might include simultaneous multithreading in its future chips; however, this was rejected in favor of their 2012 64-bit design.

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