Enable or disable HT on any GNU/Linux system at runtime

cores.sh

#!/bin/bash
#set -x
#################################################################################
#	cores.sh
#	2021 by Toni Castillo Girona, uploaded to github.
#	2018 by Toni Castillo Girona
#	<toni.castillo@upc.edu>
#################################################################################

# Only report total number of physical processors and quit:
report=0

# By default, it shows total and real cores for CPUs and it
# prints them using a SP separator.
NUMA=" "

# Don't disable ht:
htdisable=0
htenable=0

# Force enabling or disabling HT:
forceht=0

usage (){
	echo "Usage: $0 [-t] [-c #CPU] [-r #CPU] [-d #CPU] [-e #CPU] [-f] [-h]"
	echo "		 -t, reports total number of physical processors (nodes) and quits."
	echo "		 -c #CPU, reports total and real cores for physical processor #CPU."
	echo "		 -r #CPU, reports real cores for physical processor #CPU separated with commas."
	echo "		 -d #CPU [-f], disables HT on the given #CPU (requires root)."
	echo "		 -e #CPU [-f], enables HT on the given #CPU (requires root)."
	echo "		 -h, show this help message."
	echo "  Example: $0 -t"
	echo "           $0 -c 2"
	echo "           sudo $0 -d 0"
	echo "           sudo $0 -d 0 -f (does not ask if we want to do it, it just does)"
	echo "           sudo $0 -e 0"
	exit 0
}

# Let's process the arguments first:
while getopts "tc:r:d:e:fh" opt; do
	case "$opt" in
		t)
			report=1
		;;
		c)
			node=$OPTARG
			;;
		r)
			node=$OPTARG
			NUMA=","
			;;
		d)
			node=$OPTARG
			htdisable=1
			;;
		e)
			node=$OPTARG
			htenable=1
			;;
		f)
			forceht=1
			;;
		h)
			usage
			;;
	esac
done

test $# -lt 1 && usage

# Do we have numactl installed?
if [ ! -x /usr/bin/numactl ]; then
	echo "numactl is not installed. Install it first with:"
	echo -ne "\tsudo apt-get install numactl\n"
	exit 1
fi

# Total number of physical cores:
totalcores=`numactl -H|grep -E "^node [0-9]+"|cut -d" " -f2|sort|uniq|wc -l`
echo "Total physical processors on this system: ${totalcores}"
test $report -eq 1 && exit 0

# Get cores for node $node:
cores=`numactl -H|grep "node $node cpus"|cut -d":" -f2`
if [ -z "${cores}" ]; then
	echo "Physical processor $node is not a valid physical cpu."
	exit 0
fi

for c in ${cores}
do
	# grab this core information:
	cinfo=`grep .  /sys/devices/system/cpu/cpu${c}/topology/thread_siblings | tr : \\t | sed 's,^,    ,'`
	ccinfo="core:$c:${cinfo}"
	cinfos="${cinfos} `echo ${ccinfo}|tr -d ' '`"
	ccinfos="${ccinfos} ${cinfo}"
done

# This is the uniq list of cores, the real ones:
realcores=`echo $ccinfos|tr ' ' '\n'|sort|uniq`

# Show the number for the real cores:
for rcore in ${realcores}; do
	# Get its number from the first list
	rcores="${rcores}`echo $cinfos|tr ' ' '\n'|grep ":${rcore}"|head -1|cut -d":" -f2`${NUMA}"
done

# Get the list of virtualcores
# Obviously, when $cores == $rcores, no enabled virtual cores present:
vcores=`echo "${cores}, ${rcores}" | tr -d ','|tr ' ' '\n' | sort | uniq -u|tr '\n' ' '|tr -d ","`

# Show total cores and real cores:
test "${NUMA}" == " " && echo "Total Cores for processor $node: $cores"
test "${NUMA}" == " " && echo "Enabled Virtual Cores for processor $node: $vcores"
echo "Real Cores for processor  $node:  $rcores"

# Do we want to disable HT?
if [ $htdisable -eq 1 ]; then
	# If no root, abort:
	idu=`id -u`
	if [ $idu != 0 ]; then
		echo "To disable HT you need to be root".
		exit 0
	fi
	# If there are not virtual cores enabled, we cannot disable them!
	if [ -z "$vcores" ]; then
		echo -ne "All the virtual cores for processor $node already disabled!\n"
		exit 1
	fi
	# If we are not forcing the disabling of HT, we ask first:
	if [ $forceht == 0 ]; then
		echo "We are about to disable HT on physical cpu: $node"
		echo "CPU cores to be disabled: $vcores"
		echo "Are you sure? [yn]"
		read doit
	fi
	# We disable HT if we said yes or if we are forcing it:
	if [ "$doit" == "y" -o $forceht -eq 1 ]; then
		# For every non-real core, disable it:
		for vc in ${vcores}; do
			echo 0 > /sys/devices/system/cpu/cpu${vc}/online
		done
	fi	
fi

# Do we want to enable HT?
# This only makes sense when there are NOT enabled virtual cores :
if [ $htenable -eq 1 ]; then
	# If no root, abort:
	idu=`id -u`
	if [ $idu != 0 ]; then
		echo "To enable HT you need to be root".
		exit 0
	fi
	# No enabled virtual cores, so do nothing:
	if [ ! -z "$vcores" ]; then
		echo -ne "All the virtual cores for processor $node already enabled!\n"
		exit 1
	fi
	# Do we want to ask before enabling them?
	if [ $forceht -eq 0 ]; then
		echo "We are about to enable HT on physical cpu: $node"
		echo "Are you sure? [yn]"
		read doit
	fi
	if [ "$doit" == "y" -o $forceht -eq 1 ]; then
		# Knowing the real cores, iterate thorugh all the cores and
		# enable those that are disabled... 
		cpus=`ls -d /sys/devices/system/cpu/cpu*/online`
		for c in ${cpus}; do	
			# If not enabled, we enable it:
			enabled=`cat -v $c`
			if [ $enabled -eq 0 ]; then
				echo 1 > $c
				#Add this core to the enabled virtual cores:
				vc=`echo -ne $c|cut -d"/" -f6`
				vcores="${vcores} ${vc:3}"
			fi
		done
		# We now show all the enabled Virtual Cores:
		echo "Enabled Virtual Cores on processor $node: ${vcores}"
	fi
fi

exit 0