How does turbo boost interact with hyperthreading?

[dderidex]

As above.

Motherboards for Intel's Sandy Bridge chips have BIOS options to set CPU multiplier per core usage levels.

IE., 39/38/37/36 - when only one core is in use, multiplier is '39'; when two are in use, multiplier is '38; etc.

Question is - how does this interact with hyperthreading? If there are two heavy threads in use...is it possible they would be on the same core, so still use the 'one core' clock speed? Or would it be using the 'two cores' clock speed?

 

[Forceman]

The clock speed is based on the core, so if the scheduler put two threads on the same core it would still turbo to the single core speed. However, the scheduler should be smart enough to put the threads on different cores, since a HT "core" isn't as effective as an actual one, and then it would turbo to the 2 core speed.

In other words - HT has no effect on the turbo multiplers.