[mscrivo]

AVX code is known to make the CPU run way hotter than usual. Perhaps that caused throttling that made general code running at the same time, or within a short span thereafter, perform worse?

[pkaye]

That is one theory I had but i'm not sure how to determine if CPU is throttling (on Ubuntu Linux.)

[thecompilr]

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.

[pkaye]

I'll try that out. Thanks.

[lathiat]

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'

[dpayne]

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.