[craig@ayaki tmp]$ echo -n "direct=f Readahead: "; sudo blockdev --getra /dev/sda; for (( x = 2; x < 14; x++ )); do echo $((1<<x))kb blocks; echo 1 | sudo tee -a /proc/sys/vm/drop_caches >/dev/null; time ./io $((1<<x)) test_file; done
direct=f Readahead: 4096
4kb blocks
read: Success

real	0m10.178s
user	0m0.015s
sys	0m1.167s
8kb blocks
read: Success

real	0m10.037s
user	0m0.006s
sys	0m1.180s
16kb blocks
read: Success

real	0m10.303s
user	0m0.004s
sys	0m1.230s
32kb blocks
read: Success

real	0m10.870s
user	0m0.003s
sys	0m1.148s
64kb blocks
read: Success

real	0m10.194s
user	0m0.004s
sys	0m1.080s
128kb blocks
read: Success

real	0m10.401s
user	0m0.004s
sys	0m1.233s
256kb blocks
read: Success

real	0m10.087s
user	0m0.000s
sys	0m1.202s
512kb blocks
read: Success

real	0m10.061s
user	0m0.001s
sys	0m1.280s
1024kb blocks
read: Success

real	0m10.161s
user	0m0.003s
sys	0m1.301s
2048kb blocks
read: Success

real	0m10.246s
user	0m0.000s
sys	0m1.291s
4096kb blocks
read: Success

real	0m9.996s
user	0m0.002s
sys	0m1.366s
8192kb blocks
read: Success

real	0m9.997s
user	0m0.001s
sys	0m1.599s