Comment by chaps

Here's how I do it:

  xargs -I'hostname' -a hosts.txt -P128 bash -c "ssh 'hostname' find / -type f -mmin -20 | xargs -P128 -Ifilename grep -cHia error filename 2>/dev/null | sed 's/^/hostname:/' ; :" | sort -nrk3 -t':'