#!/usr/bin/env bash
# Written by Draco (tytydraco @ GitHub)

# Log in red
err() {
	echo -e " \e[91m*\e[39m $*"
}

# Log in orange
warn() {
	echo -e " \e[93m*\e[39m $*"
}

# Log in white and continue (unnecessary)
dbg() {
	echo -e " \e[92m*\e[39m $*"
}

# Safely write value to file
_write() {
	# Bail out if file does not exist
	[[ ! -f "$1" ]] && return 1

	# Fetch the current key value
	local curval
	curval="$(cat "$1" 2> /dev/null)"

	# Bail out if value is already set
	if [[ "$curval" == "$2" ]]
	then
		warn "Skipping write $1: $curval → $2"
		return 0
	fi

	# Write the new value
	if ! echo "$2" > "$1" 2> /dev/null
	then
		err "Failed to write $1: $curval → $2"
		return 1
	fi

	dbg "Successfully wrote $1: $curval → $2"
}

# Background fork write function
write() {
	if [[ "$SYNC" -eq 1 ]]
	then
		_write "$@"
	else
		_write "$@" &
	fi
}

usage() {
	echo -n "Usage: $(basename "$0") [OPTIONS]
Options:
  -s			Synchronous mode
  -h			Show usage
"
}

# Check for root permissions
if [[ "$(id -u)" -ne 0 ]]
then
	err "No root permissions. Exiting."
	exit 1
fi

while getopts ":sh" opt; do
	case $opt in
		s)
			SYNC=1
			;;
		h)
			usage
			exit 0
			;;
		*)
			usage
			exit 1
			;;
	esac
done
shift $((OPTIND - 1))

# Kernel
write /proc/sys/kernel/perf_cpu_time_max_percent 5
write /proc/sys/kernel/sched_autogroup_enabled 0
write /proc/sys/kernel/sched_child_runs_first 1
write /proc/sys/kernel/sched_tunable_scaling 0
write /proc/sys/kernel/sched_latency_ns 1000000
write /proc/sys/kernel/sched_min_granularity_ns 100000
write /proc/sys/kernel/sched_wakeup_granularity_ns 100000
write /proc/sys/kernel/sched_migration_cost_ns 5000000
write /proc/sys/kernel/sched_min_task_util_for_colocation 0
write /proc/sys/kernel/sched_nr_migrate 8
write /proc/sys/kernel/sched_schedstats 0

# VM
write /proc/sys/vm/dirty_background_ratio 10
write /proc/sys/vm/dirty_ratio 30
write /proc/sys/vm/dirty_expire_centisecs 3000
write /proc/sys/vm/dirty_writeback_centisecs 3000
write /proc/sys/vm/page-cluster 0
write /proc/sys/vm/reap_mem_on_sigkill 1
write /proc/sys/vm/stat_interval 10
write /proc/sys/vm/swappiness 100
write /proc/sys/vm/vfs_cache_pressure 60

# Scheduler features
if [[ -f "/sys/kernel/debug/sched_features" ]]
then
	write /sys/kernel/debug/sched_features NEXT_BUDDY
	write /sys/kernel/debug/sched_features TTWU_QUEUE
	write /sys/kernel/debug/sched_features HRTICK
fi

# CPU
for cpu in /sys/devices/system/cpu/cpu*/cpufreq/
do
	avail_govs="$(cat "${cpu}scaling_available_governors")"
	if [[ "$avail_govs" == *"schedutil"* ]]
	then
		_write "${cpu}scaling_governor" schedutil
		write "${cpu}schedutil/up_rate_limit_us" 5000
		write "${cpu}schedutil/down_rate_limit_us" 5000
		write "${cpu}schedutil/rate_limit_us" 5000
		write "${cpu}schedutil/hispeed_load" 90
		write "${cpu}schedutil/hispeed_freq" "$(cat "${cpu}cpuinfo_max_freq")"
	elif [[ "$avail_govs" == *"interactive"* ]]
	then
		_write "${cpu}scaling_governor" interactive
		write "${cpu}interactive/min_sample_time" 5000
		write "${cpu}interactive/go_hispeed_load" 90
		write "${cpu}interactive/hispeed_freq" "$(cat "${cpu}cpuinfo_max_freq")"
	fi
done

# I/O
for queue in /sys/block/*/queue/
do
	avail_scheds="$(cat "${queue}scheduler")"
	for sched in cfq noop kyber bfq mq-deadline none
	do
		if [[ "$avail_scheds" == *"$sched"* ]]
		then
			_write "${queue}scheduler" "$sched"
			break
		fi
	done
	write "${queue}iostats" 0
	write "${queue}read_ahead_kb" 64
	write "${queue}nr_requests" 64
done

exit 0