Its says its a hidden file.

Did you used "ls -la .hxmperf.txt" from your home directory ?
if its not in your home directory, try find. "find . -name .hxm*txt"

EDIT: Didn't saw the link properly, it says you have to create .hxmperf.txt file if you want to device mention in the file. so create it manually with name,mac address.