It is csv module: reading file seems like half the speed of python. So
real slowness is coming from csv

count = 0
File.open('x.csv') do |reader|
reader.each {|data| count += 1}
end
p count


[root@taamportable GMS]# time ruby x1.rb
26908

real    0m0.077s
user    0m0.060s
sys     0m0.016s


[root@taamportable GMS]# time python x1.py
26908

real    0m0.041s
user    0m0.032s
sys     0m0.010s