Can Intel Turbo Boost frequency for all cores be lower than the base frequency?

Solution 1:

It depends on two things, for the most part: whether you're using AVX-512, and how hot the CPU gets when under a sustained load.

If you keep the CPU's reported temperature below its rated Tcase temperature, and you're not using AVX-512, it'll run at 2.9GHz on an all-core load all day long. The moment you execute an AVX-512 instruction, it'll drop to 2.6GHz.

AVX-512 execution is handled by dedicated parts of the CPU silicon that don't do anything else; they produce a ludricrous amount of heat, and they can't run at quite the same speed as the rest of the chip. As a result, every Intel CPU with AVX-512 lowers clocks by a few hundred MHz when it's in use.

The good news is that there's really not that much outside of specialized/HPC workloads that ever touches AVX-512, so you'll probably never notice :)