Earlier quoted context omitted.
In my experience SMT is still faster for most workloads even with the mitigations.
It's a common misunderstanding that the CPU suddenly has twice as large performance envelope when SMT is enabled. Only specialized software/scenarios will tangibly benefit from the parasitic gains of SMT-induced extra parallelization, e.g. video encoders like x264 or CPU-bound raytracers to name a few examples. These gains typically amount to about 15-20% at the very extreme end. In some cases you'll see a performanc…
> video encoders like x264 or CPU-bound raytracers to name a few examples. These gains typically amount to about 15-20% at the very extreme end.
Normally those types of compute heavy processes, data streamlined, processes don’t see much benefit from SMT. After all SMT only provides a performance benefit by allowing the CPU to pull from two distinct chains of instructions, and fill the pipeline gaps from one thread, with instructions from the other thread. It’s effectively instruction-by-instruction scheduling of two different threads.
But if you’re running an optimised and efficient process that doesn’t have significant unpredictable branching, or significant unpredictable memory operations. Then SMT offers you very little because the instruction pipeline for each thread is almost fully packed, offering few opportunities to schedule instructions from a different thread.