> AVX2 had downclocking issues when it first appeared too - but these were rapidly mitigated and forgotten.

Speaking of Daniel Lemire, he recently published a paper https://arxiv.org/abs/1910.05109 mentioning downclocking in section 4:

> On some Intel processors, AVX-512 instructions are subject to downclocking: whenever AVX-512 instructions are executed, the processor lowers its frequency. We do not observe any downclocking on our processor, nor did we find any Intel documentation referencing downclocking for this processor. To test for downclocking, we used the avx-turbo benchmarking tool: it reports the processor frequency after issuing long sequences of expensive instructions of various types,including AVX-512 multiplication and floating-point instructions.