#!/bin/bash
#
# cpu-ht-enable [0|1]
#
# Turn all hyperthreading cores on or off.
#
# See
# https://www.golinuxhub.com/2018/01/how-to-disable-or-enable-hyper.html
# https://serverfault.com/questions/235825/disable-hyperthreading-from-within-linux-no-access-to-bios
# https://askubuntu.com/questions/942728/disable-hyper-threading-in-ubuntu
#
# Stress tests:
# stress-ng --cpu 12 --io 1 --vm 1 --timeout 10s
#    --perf
#    --vm-bytes 128M
#    --log-file OUTPUT
#
# Copyright (C) by Volker Kuhlmann
#               http://volker.top.geek.nz/contact.html
# All rights reserved.
# Released under the terms of the GNU General Public License (GPL) Version 2.
# See http://www.gnu.org/ for details.
#
# Volker Kuhlmann
#   1.0, 20 May 2019  Created.
#   1.1, 22 May 2019  Stress test comments. Help output. Exit !=0 if error.
#


Help() {
    echo "
Usage: ${0##*/} [0|1|off|on]
"
}

show_states() {
    echo "
CPUs present: `cat /sys/devices/system/cpu/present`
CPUs online:  `cat /sys/devices/system/cpu/online`
CPUs offline: `cat /sys/devices/system/cpu/offline`
"
}

cpu_off() {
    local file="/sys/devices/system/cpu/cpu0/topology/thread_siblings_list"
    if [ ! -e "$file" ]; then
    	echo 1>&2 "Doesn't exist: $file"
	exit 2
    fi

    local cpu ret=0
    for cpu in $(
    	grep . /sys/devices/system/cpu/cpu*/topology/thread_siblings_list \
	| sort -n -t ',' -k 2 -u \
	| grep , \
	| cut -d, -f2
	); do
	echo "CPU $cpu -> $state"
	echo -n "$state" >"/sys/devices/system/cpu/cpu$cpu/online"
	ret=$?
	test $ret -eq 0 || return $ret
    done
}

cpu_on() {
    local cpu cpuon state ret=0
    for cpuon in $(
    	ls -1 /sys/devices/system/cpu/cpu*/online \
	| sort -t/ -k 6.4n
	); do
	cpu="${cpuon#/sys/devices/system/cpu/cpu}"
	cpu="${cpu%%/*}"
	state="`cat /sys/devices/system/cpu/cpu$cpu/online`"
	test "$state" -eq 1 && continue
	state=1
	echo "CPU $cpu -> $state"
	echo -n "$state" >"/sys/devices/system/cpu/cpu$cpu/online"
	ret=$?
	test $ret -eq 0 || return $ret
    done
}

cpu_on_off() {
    local state="$1"

    case "$state" in
    	0|[Oo]ff)
	    state=0
	    cpu_off
	    ;;
	1|[Oo]n)
	    state=1
	    cpu_on
	    ;;
	"")
	    Help
	    exit
	    ;;
	*)
	    Help
	    exit 1
	    ;;
    esac
}


show_states
cpu_on_off "$@" || exit
show_states

exit


grep -q '^flags.*[[:space:]]ht[[:space:]]' /proc/cpuinfo

grep -H . /sys/devices/system/cpu/cpu*/topology/thread_siblings_list | sort -n -t ',' -k 2 -u

grep -H . /sys/devices/system/cpu/cpu*/topology/thread_siblings_list | sort -n -t ',' -k 2 -u | grep , | cut -d, -f2

cat /sys/devices/system/cpu/cpu*/online

more \
/sys/devices/system/cpu/present \
/sys/devices/system/cpu/online \
/sys/devices/system/cpu/offline