If you are receiving errors about missing of /sys/kernel/debug, make sure that debugfs is mounted:
mount -t debugfs debugfs /sys/kernel/debug
You can alternatively use /proc/sys/vm/block_dump,
when writing 1 in this file the data capturing begins; when writing 0 the results are withdrawn to the dmesg buffer.
The script for simplicity of the data parsing can be downloaded here:
The I/O monitoring not on behalf of a scheduler, but of exhaustive processes is conveniently carried out by using the iotop utility (http://guichaz.free.fr/iotop/)