$ time ./egrep.pl --max-workers=2 -c "[aA].*[eE].*[iI].*[oO].*[uU]" /tmp/big.txt 
2195760

N-thds  2           5           10          20          30
real    0m39.068s   0m16.088s   0m8.146s    0m4.229s    0m3.084s
user    1m17.614s   1m19.624s   1m20.441s   1m21.823s   1m25.296s
sys     0m0.419s    0m0.464s    0m0.434s    0m0.526s    0m0.645s