As with all things, AVX512 involves a tradeoff: core frequency can decrease when it's in use; if properly utilized, it can realize significant performance gains

As with all things, AVX512 involves a tradeoff: core frequency can decrease when it's in use; if properly utilized, it can realize significant performance gains, but if not, can result in a reduction in performance. Don't be so quick to assume that a fence wasn't put up for a good reason.