You can either use lscpu, which is less accurate, or the best way is to check:

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

where instead of cpu0 you can write any core number, and it will give you the current frequency of that core in KHz.

I'll try that out. Thanks.

Note that with pstate /proc/cpuinfo is not reflective (not suggested here but, in the past, the MHz used to change to reflect the scaling speed). You could also look at 'powertop'

One way I've found to isolate this is to turn off turbo boost and underclock the cpu, while making sure the avx offset is set to 100%. While you would never want to run a production system like this, it does help to eliminate any issues with cpu throttling. If the avx-512 version of the program still runs slower then something else is interfering besides cpu throttling.