#!/bin/bash
#
# A script intended to provide help with characterizing a block device and
# provide help with setting IO scheduler tunbales accordingly.
#
# Author: Vivek Goyal <vgoyal@redhat.com>


generate_report_nr_procs () {
	local nr_procs=$1
	local individual_bw
	local individual_bw_copy
	local bw
	local total_bw=0

	individual_bw=`cat $TEMPFILE | sed -n "/BEGIN NR_PROCESSES=$nr_procs/,/END NR_PROCESSES=$nr_procs/p" | grep "bytes.*copied" | awk -F ',' '{print $3}' | awk '{print $1}' | sed -e :a -e '$!N;s/\n/ /;ta'`

#	echo "individual bw is $individual_bw"

	for bw in $individual_bw;do
		total_bw=`echo "$total_bw + $bw" | bc`
	done

	printf "%-8s%-10s%-60s\n" $nr_procs $total_bw "$individual_bw"
}

generate_report () {
	local i

	for ((i=1; i<=$MAX_NR_PROCESSES; i=$i*2)) {
		generate_report_nr_procs $i
	}
}

# Run the test for nr processes
run_test_nr_processes () {
	local nr_processes=$1
	local bdev_size_bytes=`blockdev --getsize64 $BLOCKDEV`
	local bdev_nr_ibs=$(($bdev_size_bytes/$BS))
	local nr_ibs_per_process=$(($bdev_nr_ibs/$nr_processes))
	local j

	# disk might be big. By default read 512MB of data per process
	local nr_blocks_to_read=$(((512*1024*1024)/$BS))

	# Run processes
	for((j=1; j<=$nr_processes; j++)) {
		local skip_mult=$(($j-1))
		local skip_blocks=$(($nr_ibs_per_process*$skip_mult))

		dd if=$BLOCKDEV of=/dev/null ibs=$BS count=$nr_blocks_to_read skip=$skip_blocks >> $TEMPFILE 2>&1 &
	}

}

start_test () {
	local i

	# Launch increasing number of dd threads. Determine device capacity
	# divide the total capacity by number of threads and let different
	# threads work on different area of block device.

	echo "Will Run up to $MAX_NR_PROCESSES readers"

	for((i=1; i<=$MAX_NR_PROCESSES; i=$i*2)) {
		echo "Running test with $i readers"
		echo "BEGIN NR_PROCESSES=$i" >> $TEMPFILE
		run_test_nr_processes $i
		wait
		echo "END NR_PROCESSES=$i" >> $TEMPFILE
	}
}

Usage () {
	echo "Usage: $0 DEVICE"
}

# Main script
if [ $# -lt 1 ];then
	Usage
	exit 1
fi

BLOCKDEV=$1
# default block size
BS=4096
TEMPFILE=`mktemp /tmp/iostune.XXXXX`
MAX_NR_PROCESSES=8

if [ ! -b "$BLOCKDEV" ];then
	echo "Error: $BLOCKDEV is not a block device."
	exit 1
fi

start_test
wait
generate_report