The bootio tool records I/O for processes during boot. To use bootio kernel must be compiled with this flags:
CONFIG_TASKSTATS=y CONFIG_TASK_DELAY_ACCT=y CONFIG_TASK_XACCT=y CONFIG_TASK_IO_ACCOUNTING=y
To use bootio make sure it's included in product config for the board. Create file /data/misc/bootio/start with a command like the following:
adb shell 'echo "$TIMEOUT $SAMPLES" > /data/misc/bootio/start'
Where the value of $TIMEOUT corresponds to the desired bootio period in seconds and $SAMPLES corresponds to the desired number of samples.
Note: /data/misc/bootio/start is not deleted automatically, so don't forget to delete it when you're done collecting data.
To see collected logs run:
adb shell bootio -p