#!/usr/bin/env bash

set -euo pipefail

change="CHANGE:"
info="INFO:"
kernel_config="/proc/config.gz"
sysctl_ref="(see \`man 5 sysctl.conf\`, \`man 5 sysctl.d\` or \`man 8 sysctl\` for reference)"

check_root() {
  if [ "$(id -u)" -eq 0 ]; then
    echo "Use this script as an unprivileged user."
    exit 1
  fi
}

check_kernel_name() {
  if [[ "$(uname -s)" != *Linux* ]]; then
    echo "This script needs to be run on a Linux system."
    exit 1
  fi
}

check_filesystems() {
  local mount_points=()
  local mount_point_data=()
  local what=""
  local where=""
  local type=""
  local options=""
  mapfile -t mount_points < <( mount |grep -E "^/dev" )
  for mount_point in "${mount_points[@]}"; do
    mapfile -d " " -t mount_point_data < <( echo "${mount_point}" )
    what="${mount_point_data[0]}"
    where="${mount_point_data[2]}"
    type="${mount_point_data[4]}"
    options="${mount_point_data[5]}"
    if [[ "$where" != /boot* ]]; then
      if [[ "$options" != *relatime* ]] && [[ "$options" != *noatime* ]]; then
        echo "$change $what mounted on $where (type $type) should use the relatime mount option for performance."
      fi
      if [[ "$type" == *fuse* ]] || [[ "$type" == *reiserfs* ]] || [[ "$type" == *vfat* ]]; then
        echo "$info $what mounted on $where (type $type) is not a good filesystem for large files or realtime use."
      fi
    fi
  done
}

check_groups() {
  local groups=""
  groups=$(groups)
  if [[ "$groups" != *audio* ]]; then
    echo "$change Add your user to the audio group. It's used for access to audio devices on most distros."
  fi
  if [[ "$groups" != *realtime* ]]; then
    echo "$info Some distributions use the realtime group for elevated resource limits."
  fi
}

check_ulimits() {
  local limits_ref="(see \`man limits.conf\` for reference)"
  if [[ "$(ulimit -t)" != "unlimited" ]]; then
    echo "$change The CPU limit for your user is not unlimited $limits_ref."
  fi
  if [[ "$(ulimit -l)" != "unlimited" ]]; then
    echo "$change The locked-in-memory limit for your user is not unlimited $limits_ref."
  fi
  if [ "$(ulimit -r)" -le 50 ]; then
    echo "$change The maximum rt priority for your user ($(ulimit -r)) is very low. Consider increasing it up to 98 $limits_ref."
  fi
}

check_vm_swappiness() {
  local minimum=10
  local proc_file="/proc/sys/vm/swappiness"
  if [ "$(cat "$proc_file")" -gt $minimum ]; then
    echo "$info Consider decreasing 'vm.swappiness<=$minimum' to prevent early write to swap $sysctl_ref."
  fi
}

check_max_user_watches() {
  local minimum=524288
  local proc_file="/proc/sys/fs/inotify/max_user_watches"
  if [ "$(cat "$proc_file")" -lt $minimum ]; then
    echo "$change Consider increasing 'fs.inotify.max_user_watches>$minimum' - the maximum amount of files inotify can watch $sysctl_ref"
  fi
}

check_cpu_governor() {
  local cpupower_ref="(see \`man cpupower\` for reference)"
  local governor=""
  local policy_no=""
  local cpu_no=""
  for governor_file in /sys/devices/system/cpu/cpufreq/policy*/scaling_governor; do
    governor="$(cat "$governor_file")"
    policy_no="$(echo "$governor_file"| cut -d'/' -f7)"
    cpu_no="${policy_no//policy}"
    if [[ "$governor" != "performance" ]]; then
      echo "$change CPU $cpu_no has governor $governor set. Set it to 'performance' $cpupower_ref."
    fi
  done
}

check_config_high_res_timers() {
  local config="CONFIG_HIGH_RES_TIMERS=y"
  local config_ref="(see \`man 7 time\` for reference)"
  if [ -e "${kernel_config}" ]; then
    if ! zgrep -q "$config" "$kernel_config"; then
      echo "$change CONFIG_HIGH_RES_TIMERS needs to be activated for your kernel $config_ref."
    fi
  else
    echo "$change $kernel_config could not be found or accessed."
  fi
}

check_config_no_hz() {
  local configs=( 'CONFIG_NO_HZ_COMMON=y' 'CONFIG_NO_HZ_FULL=y' 'CONFIG_NO_HZ=y')
  local config_ref="(see https://elinux.org/Kernel_Timer_Systems#Dynamic_ticks for reference)"
  if [ -e "${kernel_config}" ]; then
    for config in "${configs[@]}"; do
      if ! zgrep -q "$config" "$kernel_config"; then
        echo "$change $config1 needs to be set for your kernel for 'dynamic ticks' support $config_ref."
      fi
    done
  else
    echo "$change $kernel_config could not be found or accessed."
  fi
}

check_config_preempt_rt() {
  local config1="CONFIG_PREEMPT_RT=y"
  local config2="CONFIG_PREEMPT_RT_FULL=y"
  local config_ref="(see https://wiki.linuxfoundation.org/realtime for reference)"
  if [ -e "${kernel_config}" ]; then
    if ! zgrep -q "$config1" "$kernel_config" && ! zgrep -q "$config2" "$kernel_config"; then
      echo "$change The PREEMPT_RT patch set is not available on your kernel $config_ref."
    fi
  else
    echo "$change $kernel_config could not be found or accessed."
  fi
}

check_config_irq_forced_threading() {
  local config1="CONFIG_PREEMPT=y"
  local config2="CONFIG_IRQ_FORCED_THREADING=y"
  local config_ref="(see https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html for reference)"
  if [ -e "${kernel_config}" ]; then
    if zgrep -q "$config2" "$kernel_config"; then
      if ! zgrep -q "$config1" "$kernel_config" && ! grep -q "threadirqs" /proc/cmdline; then
        echo "$change Without $config1 on your kernel, you can still use the threadirqs kernel parameter $config_ref." 
      fi
    else
      echo "$change Use a kernel with $config2 $config_ref."
    fi
  else
    echo "$change $kernel_config could not be found or accessed."
  fi
}

check_legacy_timers() {
  local hpet_file="/dev/hpet"
  local rtc_file="/dev/rtc0"
  local hpet_ref="(see https://wiki.linuxaudio.org/wiki/system_configuration#timers for reference)"
  if [ ! -w "$hpet_file" ]; then
    echo "$info $hpet_file is not writable by your user. Some legacy software requires it $hpet_ref."
  fi
  if [ ! -w "$rtc_file" ]; then
    echo "$info $rtc_file is not writable by your user. Some legacy software requires it $hpet_ref."
  fi
}

check_cpu_dma_latency() {
  local dev_file="/dev/cpu_dma_latency"
  if [ ! -w "$dev_file" ]; then
    echo "$change $dev_file needs to be writable by your user to prevent deep CPU sleep states."
  fi
}

check_coupled_interrupts() {
  local interrupts=()
  local interrupt_delim=", "
  local interrupt_number=""
  local interrupt_ref="(see \`cat /proc/interrupts\` for more and consider using rtirq)"
  mapfile -t interrupts < <( cat /proc/interrupts )
  for interrupt_line in "${interrupts[@]}"; do
    interrupt_number="$(echo "$interrupt_line"| cut -d':' -f1)"
    if [[ "$interrupt_line" == *"$interrupt_delim"* ]]; then
      echo "$change IRQ$interrupt_number has coupled interrupts $interrupt_ref."
    fi
  done
}

check_irqbalance() {
  if pgrep -i irqbalance >/dev/null 2>&1; then
    echo "$change The irqbalance service is running on your system. It might interfere, so consider disabling it."
  fi
}

check_for_useful_tools() {
  local tools=( cyclictest htop iostat iotop rtirq schedtool tuna )
  for tool in "${tools[@]}";do
    if ! command -v "$tool" >/dev/null 2>&1; then
      echo "$info Consider installing and using $tool."
    fi
  done
}

check_kernel_name
check_root
check_filesystems
check_groups
check_ulimits
check_max_user_watches
check_legacy_timers
check_vm_swappiness
check_cpu_governor
check_cpu_dma_latency
check_config_high_res_timers
check_config_no_hz
check_config_preempt_rt
check_config_irq_forced_threading
check_coupled_interrupts
check_irqbalance
check_for_useful_tools