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#ActualMJP

Posted 30 December 2012 - 07:46 PM

The third one, hyperthreading, was invented by Intel, and a fake of the first one (multicore). When the CPU is only using one of the pipelines described as instruction-level parallelism and the OoOE couldn't do anything to prevent it, we've got a lot of idle pipelines.

Because those pipelines are "almost" an extra core, Hyperthreading kicks in and simulates an extra core to execute a parallel thread, but is not near in the same level as a real additional core because: 1. Not all parts of the pipeline are duplicated and 2. The main thread may actually start using those unused pipelines, leaving no spare components to dedicate to the hyperthreaded thread.
Intel claims Hyperthreading yields an average gain of 15% in performance.
Btw, if you open Task Manager in a single core system with hyperthreading, it will tell you there are two cores (the real one + fake one). In Intel Core i7 with 8 cores, it will tell you there are 16 cores (8 real ones + 8 fake ones)
Not all CPUs come with HT, in fact, most of them don't.
Just to add to this...the generic non-Intel term for this technique is "simultaneous multithreading", or "SMT" for short.

#1MJP

Posted 30 December 2012 - 07:46 PM

The third one, hyperthreading, was invented by Intel, and a fake of the first one (multicore). When the CPU is only using one of the pipelines described as instruction-level parallelism and the OoOE couldn't do anything to prevent it, we've got a lot of idle pipelines.

Because those pipelines are "almost" an extra core, Hyperthreading kicks in and simulates an extra core to execute a parallel thread, but is not near in the same level as a real additional core because: 1. Not all parts of the pipeline are duplicated and 2. The main thread may actually start using those unused pipelines, leaving no spare components to dedicate to the hyperthreaded thread.

Intel claims Hyperthreading yields an average gain of 15% in performance.

Btw, if you open Task Manager in a single core system with hyperthreading, it will tell you there are two cores (the real one + fake one). In Intel Core i7 with 8 cores, it will tell you there are 16 cores (8 real ones + 8 fake ones)

Not all CPUs come with HT, in fact, most of them don't.

 

Just to add to this...the generic non-Intel term for this technique is "simulataneous multithreading", or "SMT" for short.


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