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#1 2020-03-26 11:14:56

Registered: 2020-03-26
Posts: 3

[SOLVED] QEMU CPU Isolating hooks script doesn't work

Hey, I tried to use this: … ating_CPUs
I've created the hooks folders here:
#   - /etc/libvirt/hooks/qemu.d/win10/prepare/begin/
#   - /etc/libvirt/hooks/qemu.d/win10/release/end/
And nothing happens, I tried to find some logs, but there is nothing about hooks.
Then I read the libvirt so I did the same but in /etc/libvirt/hooks/qemu/ and again nothing.

Maybe someone knows how to run hooks under libvirt?

I tried with these locations:


The script which I use:

#!/usr/bin/env bash

# Original author: Rokas Kupstys <>
# Heavily modified by: Danny Lin <>
# This hook uses the `cset` tool to dynamically isolate and unisolate CPUs using
# the kernel's cgroup cpusets feature. While it's not as effective as
# full kernel-level scheduler and timekeeping isolation, it still does wonders
# for VM latency as compared to not isolating CPUs at all. Note that vCPU thread
# affinity is a must for this to work properly.
# Original source:!pages/
# Target file locations:
#   - $SYSCONFDIR/hooks/qemu.d/vm_name/prepare/begin/
#   - $SYSCONFDIR/hooks/qemu.d/vm_name/release/end/
# $SYSCONFDIR is usually /etc/libvirt.

TOTAL_CORES_MASK=FF             # 0-7, bitmask 0b11111111
HOST_CORES='0,4'                # Cores reserved for host
HOST_CORES_MASK=11              # 0,4, bitmask 0b00010001
VIRT_CORES='1-3,5-7'            # Cores reserved for virtual machine(s)


function shield_vm() {
    cset -m set -c $TOTAL_CORES -s machine.slice
    cset -m shield --kthread on --cpu $VIRT_CORES

function unshield_vm() {
    cset -m shield --reset

# For convenient manual invocation
if [[ "$VM_NAME" == "shield" ]]; then
elif [[ "$VM_NAME" == "unshield" ]]; then

if [[ "$VM_ACTION" == "prepare/begin" ]]; then
    echo "libvirt-qemu cset: Reserving CPUs $VIRT_CORES for VM $VM_NAME" > /dev/kmsg 2>&1
    shield_vm > /dev/kmsg 2>&1

    # the kernel's dirty page writeback mechanism uses kthread workers. They introduce
    # massive arbitrary latencies when doing disk writes on the host and aren't
    # migrated by cset. Restrict the workqueue to use only cpu 0.
    echo $HOST_CORES_MASK > /sys/bus/workqueue/devices/writeback/cpumask
    echo 0 > /sys/bus/workqueue/devices/writeback/numa

    echo "libvirt-qemu cset: Successfully reserved CPUs $VIRT_CORES" > /dev/kmsg 2>&1
elif [[ "$VM_ACTION" == "release/end" ]]; then
    echo "libvirt-qemu cset: Releasing CPUs $VIRT_CORES from VM $VM_NAME" > /dev/kmsg 2>&1
    unshield_vm > /dev/kmsg 2>&1

    # Revert changes made to the writeback workqueue
    echo $TOTAL_CORES_MASK > /sys/bus/workqueue/devices/writeback/cpumask
    echo 1 > /sys/bus/workqueue/devices/writeback/numa

    echo "libvirt-qemu cset: Successfully released CPUs $VIRT_CORES" > /dev/kmsg 2>&1

Last edited by Muata (2020-03-26 13:47:44)


#2 2020-03-26 11:46:25

From: Netherlands, Europe
Registered: 2005-10-04
Posts: 7,818

Re: [SOLVED] QEMU CPU Isolating hooks script doesn't work

You did build & install cpuset or cpuset-git aur package ?

Multi-init booting with apg Openrc and systemd coexisting
Automounting : not needed, i prefer pmount
Aur helpers : makepkg + my own local repo === rarely need them


#3 2020-03-26 11:59:54

Registered: 2020-03-26
Posts: 3

Re: [SOLVED] QEMU CPU Isolating hooks script doesn't work

Yes, cpuset-git

 cset: Cpuset (cset) 1.6 

Last edited by Muata (2020-03-26 12:00:07)


#4 2020-03-26 12:07:39

Registered: 2020-03-26
Posts: 3

Re: [SOLVED] QEMU CPU Isolating hooks script doesn't work

Ok, I've fixed by myself, maybe someone will have the same problem so:

I've changed the name of the script  from to 'qemu'(before qemu was a folder) on the /etc/libvirt/hooks and now is working.

Last edited by Muata (2020-03-27 16:32:54)


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