Tag Archives: ProxMox

Threadripper / Epyc processor core optimization

I had a pet project (folding@home) where I wanted to maximize computing power. I became frustrated with default CPU scheduling of my folding@home threads. Ideal performance would keep similar threads on the same CPU, but the threads were jumping all over the place, which was impacting performance.

Step one was to figure out which threads belonged to which physical cores. I found on this site that you can use cat to find out what your “sibling threads” are:

cat /sys/devices/system/cpu/cpu{0..15}/topology/thread_siblings_list

The above command is for my Threadripper & Epyc systems, which each have 16 cores hyperthreaded to 32 cores. Adjust the {0..15} number to match your number of cores (core 0 being the fist core.) This was my output:

cat /sys/devices/system/cpu/cpu{0..15}/topology/thread_siblings_list

0,16
1,17
2,18
3,19
4,20
5,21
6,22
7,23
8,24
9,25
10,26
11,27
12,28
13,29
14,30
15,31

Now that I know the sibling threads are offset by 16, I can use this information to optimize my folding@home VMs. I modified my CPU pinning script to take this into consideration. The script ensures that each VM is pinned to only use sibling threads (ensuring they all stay on the same physical CPU.)

This script should be used with caution. It pins processes to specific CPUs, which limits the kernel scheduler’s ability to move things around if needed. If configured badly this can cause the machine to lock up or VMs to be terminated.

I saw some impressive results spinning up four separate 8 core VMs and pinning them to sibling cores using this script. It almost doubled the rate at which I completed folding@home work units.

And now, the script:

#!/bin/bash
#Properly assign CPU cores to their respective die for EPYC/Threadripper systems
#Based on how hyperthreads are done in these systems
#cat /sys/devices/system/cpu/cpu{0..15}/topology/thread_siblings_list

#The script takes two arguments - the ID of the Proxmox VM to modify, and the core to begin the VM on
#If running this against multiple VMs, make sure to increment this second number by half of the cores of the previous VM
#For example, if I have one 8 core VM and I run this script specifying 0 for the offset, if I spin up a second VM, the second argument would be 4
#this would ensure the second VM starts on core 4 (the 5th core) and assigns sibling cores to match

set -eo pipefail

#take First argument as which VMID to pin CPU cores to, the second argument is which core to start pinning to
VMID=$1
OFFSET=$2

#Determine offset for sibling threads
SIBLING_THREAD_OFFSET=$(cat /sys/devices/system/cpu/cpu0/topology/thread_siblings_list| sed 's/,/ /g' | awk '{print $2}')

#Function to determine number of CPU cores a VM has
cpu_tasks() {
	expect <<EOF | sed -n 's/^.* CPU .*thread_id=\(.*\)$/\1/p' | tr -d '\r' || true
spawn qm monitor $VMID
expect ">"
send "info cpus\r"
expect ">"
EOF
}

#Only act if VMID & OFFSET are set
if [[ -z $VMID  || -z $OFFSET ]]
then
	echo "Usage: cpupin.sh <VMID> <OFFSET>"
	exit 1
else
	#Get PIDs of each CPU core for VM, count number of VM cores, and get even/odd PIDs for assignment
	VCPUS=($(cpu_tasks))
	VCPU_COUNT="${#VCPUS[@]}"
	VCPU_EVEN_THREADS=($(for EVEN_THREAD in "${VCPUS[@]}"; do echo $EVEN_THREAD; done | awk '!(NR%2)'))
	VCPU_ODD_THREADS=($(for ODD_THREAD in "${VCPUS[@]}"; do echo $ODD_THREAD; done | awk '(NR%2)'))

	if [[ $VCPU_COUNT -eq 0 ]]; then
		echo "* No VCPUS for VM$VMID"
		exit 1
	fi

	echo "* Detected ${#VCPUS[@]} assigned to VM$VMID..."
	echo "* Resetting cpu shield..."

	#Start at offset CPU number, assign odd numbered PIDs to their own CPU thread, then increment CPU core number
	#0-3 if offset is 0, 4-7 if offset is 4, etc
	ODD_CPU_INDEX=$OFFSET
	for PID in "${VCPU_ODD_THREADS[@]}"
	do
		echo "* Assigning ODD thread $ODD_CPU_INDEX to $PID..."
		taskset -pc "$ODD_CPU_INDEX" "$PID"
		((ODD_CPU_INDEX+=1))
	done

	#Start at offset + CPU count, assign even number PIDs to their own CPU thread, then increment CPU core number
	#16-19 if offset is 0,	20-23 if offset is 4, etc
	EVEN_CPU_INDEX=$(($OFFSET + $SIBLING_THREAD_OFFSET))
	for PID in "${VCPU_EVEN_THREADS[@]}"
	do
		echo "* Assigning EVEN thread $EVEN_CPU_INDEX to $PID..."
		taskset -pc "$EVEN_CPU_INDEX" "$PID"
		((EVEN_CPU_INDEX+=1))
	done
fi

proxmox openvswitch bond

Recently I had to switch my Proxmox server which was using Linux bonds to using openvswitch. These are my notes:

Install openvswitch:

apt install openvswitch-switch

Configure openvswitch to bond interfaces and use VLANs using https://pve.proxmox.com/wiki/Open_vSwitch as an example:

allow-vmbr0 bond0
iface bond0 inet manual
	ovs_bonds enp4s0f0 eno1
	ovs_type OVSBond
	ovs_bridge vmbr0
	ovs_options bond_mode=active-backup

auto lo
iface lo inet loopback

iface eno1 inet manual

iface enp4s0f0 inet manual

allow-ovs vmbr0
iface vmbr0 inet manual
	ovs_type OVSBridge
	ovs_ports bond0 vlan50 vlan10

#Proxmox communication
allow-vmbr0 vlan50
iface vlan50 inet static
  ovs_type OVSIntPort
  ovs_bridge vmbr0
  ovs_options tag=50
  ovs_extra set interface ${IFACE} external-ids:iface-id=$(hostname -s)-${IFACE}-vif
  address 10.0.50.2
  netmask 255.255.255.0
  gateway 10.0.50.1

#Storage network
allow-vmbr0 vlan10
iface vlan10 inet static
  ovs_type OVSIntPort
  ovs_bridge vmbr0
  ovs_options tag=10
  ovs_extra set interface ${IFACE} external-ids:iface-id=$(hostname -s)-${IFACE}-vif
  address 192.168.10.2
  netmask 255.255.255.0

List active interface:

ovs-appctl bond/show bond0

Update 3/14/2020

I realized that openvswitch won’t fail back over to the original slave once it comes back online. I couldn’t for the life of me find the equivalent of bond-primary syntax for openvswitch; however I did find this command:

ovs-appctl list-commands

which reveals this command:

bond/set-active-slave port slave

So you can manually fallback using this command:

ovs-appctl bond/set-active-slave bond0 enp4s0f1

proxmox bond not present fix

I really banged my head on the wall on this one. I recently decided to re-architect my networking setup in proxmox to utilize bonded network configuration. I followed this writeup exactly. The problem is it didn’t work.

I would copy the example exactly, only changing the interface name, and yet every time I tried to start the networking service I would get this lovely error:

rawdevice bond0 not present

I finally found on the Debian Wiki one critical line :

First install the ifenslave package, necessary to enable bonding

For some reason the ProxMox howtos don’t speak of this – I guess because it comes installed by default. I discovered, however, that if you install ifupdown2 it removes ifenslave. I had installed ifupdown2 in the past to reload network configuration without rebooting. Aha!

I re-installed ifenslave (which removed ifupdown2 and re-installed ifupdown) and suddenly, the bond worked!

Bond not falling back to primary intrerface

I had configured my bond in active – backup mode. I wanted it to prefer the faster link, but if there was a failure in that link it wouldn’t switch back automatically (thanks to this site for showing me the command to check:

cat /proc/net/bonding/bond0

I read again in Debian bonding wiki that I needed to add this directive to the bond:

        bond-primary enp2s0

Here is my complete working active-backup configuration, assigning vlan 2 to the host, and making enp2s0 (the 10gig nic) the primary, with a 1gig backup (eno1)

auto bond0
iface bond0 inet manual
        slaves enp2s0 eno1
        bond-primary enp2s0
        bond_miimon 100
        bond_mode active-backup

iface bond0.2 inet manual

auto vmbr0v2
iface vmbr0v2 inet static
        address 192.168.2.2
        netmask 255.255.255.0
        gateway 192.168.2.1
        bridge_ports bond0.2
        bridge_stp off
        bridge_fd 0

auto vmbr0
iface vmbr0 inet manual
        bridge_ports bond0
        brideg_stp off
        bridge_fd 0

migrate between amd & intel in proxmox

I recently acquired an Intel based server and plugged it into my AMD-based Proxmox cluster. I ran into an issue transferring from AMD to Intel boxes (the other direction worked fine.) After a few moments, every VM that moved from AMD to Intel would kernel panic.

Fortunately I found here that the fix is to add a few custom CPU flags to your VMs. Once I did this they could move back and forth freely (assuming they had the kvm64 CPU assigned to them – host obviously won’t work.)

qm set *VMID* --args "-cpu 'kvm64,+ssse3,+sse4.1,+sse4.2,+x2apic'"

Fix proxmox iommu operation not permitted

In trying to passthrough some LSI SAS cards to a VM I kept receiving this error:

kvm: -device vfio-pci,host=0000:03:00.0,id=hostpci0,bus=ich9-pcie-port-1,addr=0x0,rombar=0: vfio 0000:03:00.0: failed to setup container for group 7: Failed to set iommu for container: Operation not permitted

I found on this post that the fix is to add a line to /etc/modprobe.d/vfio.conf with the following:

options vfio_iommu_type1 allow_unsafe_interrupts=1

then reboot the host. It worked in my case!

Proxmox HA management script

I was a bit frustrated at the lack of certain functions of ProxMox. I wanted an easy way to tag a VM and manage that tag as a group. My solution was to create HA groups for VMs with various functions. I can then manage the group and tell them to migrate storage or turn off & on.

I wrote a script to facilitate this. Right now it only covers powering on, powering off, and migrating the location of the primary disk, but more is to come.

Here’s what I have so far:

#!/bin/bash
#Proxmox HA management script
#Migrates storage, starts, or stops Proxmox HA groups based on the name and function passed to it.
#Usage: manage-HA-group.sh <start|stop|migrate> <ha-group-name> [local|remote]

#Change to the name of your local storage (for migrating from remote to local storage)
LOCAL_STORAGE_NAME="pve-1TB"

function get_vm_name() {
    #Determine the name of the VMID passed to this function
    VM_NAME=$(qm config "$1" | grep '^name:' | awk '{print $2}')
}

function get_group_VMIDs() {
    #Get a list of VMIDs based on the name of the HA group passed to this function
    group_VMIDs=$(ha-manager config | grep -B1 "$1" | grep vm: | sed 's/vm://g')
}

function group_power_state() {
    #Loop through members of HA group passed to this function
    for group in "$1" 
    do
        get_group_VMIDs "$group"
        for VM in $group_VMIDs
        do
            get_vm_name "$VM"
            echo "$OPERATION $VM_NAME in HA group $group"
            ha-manager set $VM --state $VM_STATE
        done
    done
}

function group_migrate() {
    #This function migrates the VM's first disk (scsi0) to the specified location (local/remote)
    #TODO String to determine all disk IDs:  qm config 115 | grep '^scsi[0-9]:' | tr -d ':' | awk '{print $1}'
    disk="scsi0"    

    #Loop through each VM in specified group name (second argument passed on CLI)
    for group in "$2" 
    do
        get_group_VMIDs "$group"
        for VM in $group_VMIDs
        do
            #Determine the names of each VM in the HA group
            get_vm_name "$VM"

            #Set storage location based on argument
            if [[ "$3" == "remote" ]]; then
                storage="$VM_NAME"
            else
                storage="$LOCAL_STORAGE_NAME"
            fi

            #Move primary disk to desired location
            echo "Migrating $VM_NAME to "$3" storage"
            qm move_disk $VM $disk $storage --delete=1

        done
    done
}

case "$1" in 
    start)
        VM_STATE="started"
        OPERATION="Starting"
        group_power_state "$2" 
        ;;
    stop)
        VM_STATE="stopped"
        OPERATION="Stopping"
        group_power_state "$2"
        ;;
    migrate)
        case "$3" in
            local|remote)
                group_migrate "$@"
                ;;
            *)
                echo "Usage: manage-HA-group.sh migrate <ha-group-name> <local|remote>"
                ;;
        esac        
    ;;
    *)
        echo "Usage: manage-HA-group.sh <start|stop|migrate> <ha-group-name> [local|remote]"
        exit 1
        ;;
esac

proxmox 6 NVIDIA GPU passthrough fix

I upgraded to ProxMox 6.0 and to my dismay my Windows VM suddenly began receiving the dreaded Code 43 error. After much digging I finally found this post on the ProxMox forums which outlines what needs to happen.

In my case, all I needed to do was tweak my machine type. There is no GUI option to do this, so it had to be done in the command line:

qm set <VM_ID> -machine pc-q35-3.1

That was all it took!

The forum also suggested a few other things if that didn’t work. I didn’t end up needing them but I’ll put them here in case it’s helpful:

Add args to your VM config file:

args: -cpu 'host,+kvm_pv_unhalt,+kvm_pv_eoi,hv_vendor_id=NV43FIX,kvm=off'

Add a few options to the CPU line:

cpu: host,hidden=1,flags=+pcid,hv-vendor-id=proxmox

With the above settings I also discovered there is no need to have x-vga=on anymore. This allows you to have both the regular VM console and your graphics card if you so desire.

Run startup / shutdown on every VM in PRoxmox HA group

I wanted to run a stop operation on all VMs in one of my HA groups in Proxmox and was frustrated to see there was no easy way to do so. I wrote a quick & dirty bash script that will let me start & stop all VMs within an HA group to do what I wanted.

#!/bin/bash
#Proxmox HA start/stop script
#Takes first argument of the operation to do (start / stop) and any additional arguments for which HA group(s) to do it on, then acts as requested.

if [[ "$1" != "start" && "$1" != "stop" ]]; then
    echo "Please provide desired state (start | stop)"
    exit 1
fi

if [ "$1" == "start" ]; then
    VM_STATE="started"
    OPERATION="Starting"
elif [ "$1" == "stop" ]; then
    VM_STATE="stopped"
    OPERATION="Stopping"
else exit 1 #should not ever get here
fi

#Loop through each argument except for the first
for group in "${@:-1}" 
do
    group_members=$(ha-manager config | grep -B1 $group | grep vm: )
    for VM in $group_members
    do
        echo "$OPERATION $VM in HA group $group"
        ha-manager set $VM --state $VM_STATE
    done
done

proxmox suspend & resume scripts

Update 12/17/2019: Added logic to wait for VM to be suspended before suspending the shypervisor

Update 12/8/2019: After switching VMs I needed to tweak the pair of scripts. I modified it to make all the magic happen on the hypervisor; the VM simply needs to SSH into the hypervisor and call the script. The hypervisor now also needs access to SSH via public key to the VM to tell it to suspend.

#!/bin/sh
#ProxMox suspend script part 1 of 2
#To be run on the VM 
#All this does is call the suspend script on the hypervisor
#This could also just be a bash alias

####### Variables #########
HYPERVISOR=        #Name / IP of the hypervisor
SSH_USER=          #User to SSH into hypervisor as
HYPERVISOR_SCRIPT= #Path to part 2 of the script on the hypervisor

####### End Variables ######

#Execute server suspend script
ssh $SSH_USER@$HYPERVISOR "$HYPERVISOR_SCRIPT" &
#!/bin/bash
#ProxMox suspend script part 2 of 2
#Script to run on the hypervisor, it waits for VM to suspend and then suspends itself
#It relies on passwordless sudo configured on the VM as well as SSH keys to allow passwordless SSH access to the VM from the hypervisor
#It resumes the VM after it resumes itself
#Called from the VM

########### Variables ###############

VM=             #Name/IP of VM to SSH into
VM_SSH_USER=    #User to ssh into the vm with
VMID=           #VMID of VM you wish to suspend

########### End Variables############

#Tell guest VM to suspend
ssh $VM_SSH_USER@$VM "sudo systemctl suspend"

#Wait until guest VM is suspended, wait 5 seconds between attempts
while [ "$(qm status $VMID)" != "status: suspended" ]
do 
    echo "Waiting for VM to suspend"
    sleep 5 
done

#Suspend hypervisor
systemctl suspend

#Resume after shutdown
qm resume $VMID

I have a desktop running ProxMox. My GUI is handled via a virtual machine with physical hardware passed through it. The challenge with this setup is getting suspend & resume to work properly. I got it to work by suspending the VM first, then the host; on resume, I power up the host first, then resume the VM. Doing anything else would cause hardware passthrough problems that would force me to reboot the VM.

I automated the suspend process by using two scripts: one for the VM, and one for the hypervisor. The first script is run on the VM. It makes an SSH command to the hypervisor (thanks to this post) to instruct it to run the second half of the script; then initiates a suspend of the VM.

The second half of the script waits a few seconds to allow the VM to suspend itself, then instructs the hypervisor to also go into suspend. I had to split these into two scripts because once the VM is suspended, it can’t issue any more commands. Suspending the hypervisor must happen after the VM itself is suspended.

Here is script #1 (to be run on the VM) It assumes you have already set up a private/public key pair to allow for passwordless login into the hypervisor from the VM.

#!/bin/sh
#ProxMox suspend script part 1 of 2
#Tto be run on the VM so it suspends before the hypervisor does

####### Variables #########
HYPERVISOR=HYPERVISOR_NAME_OR_IP
SSH_USER=SSH_USER_ON_HYPERVISOR
HYPERVISOR_SCRIPT_LOCATION=NAME_AND_LOCATION_OF_PART2_OF_SCRIPT

####### End Variables ######

#Execute server suspend script, then suspend VM
ssh $SSH_USER@$HYPERVISOR  $HYPERVISOR_SCRIPT_LOCATION &

#Suspend
systemctl suspend

Here is script #2 (which script #1 calls), to be run on the hypervisor

#!/bin/bash
#ProxMox suspend script part 2 of 2
#Script to run on the hypervisor, it waits for VM to suspend and then suspends itself
#It resumes the VM after it resumes itself

########### Variables ###############

#Specify VMid you wish to suspend
VMID=VMID_OF_VM_YOU_WANT_TO_SUSPEND

########### End Variables############

#Wait 5 seconds before doing anything to allow for VM to suspend
sleep 5

#Suspend hypervisor
systemctl suspend

#Resume after shutdown
qm resume $VMID

It works on my machine 🙂

Primary VGA passthrough in ProxMox

I recently decided to amplify my VFIO experience by experimenting with passing my primary display adapter to a VM in proxmox. Previously I had just run tasksel on the proxmox host itself to install a GUI. I wanted better separation from the server side of proxmox and the client side. I also wanted to be able to distro-hop while maintaining the proxmox backend.

Initially I tried following my guide for passing through a secondary graphics card but ran into a snag. It did not work with my primary card and kept outputting these errors:

device vfio-pci,host=09:00.0,id=hostdev0,bus=pci.4,addr=0x0: Failed to mmap 0000:09:00.0 BAR 1. Performance may be slow

After much digging I finally found this post which explained I needed to unbind a few things for it to work properly:

echo 0 > /sys/class/vtconsole/vtcon0/bind
echo 0 > /sys/class/vtconsole/vtcon1/bind
echo efi-framebuffer.0 > /sys/bus/platform/drivers/efi-framebuffer/unbind

After more searching I found this post on reddit which had a nifty script for automating this when VM startup is desired. I tweaked it a bit to suit my needs.

Find your IDs for GPU by doing lspci and looking for your adapter. Find the IDs by running lspci -n -s <GPU location discovered with lspci>. Lastly VMID is the promxox ID for the VM you wish to start.

#!/bin/sh
#Script to launch Linux desktop
#Adapted from from https://www.reddit.com/r/VFIO/comments/abfjs8/cant_seem_to_get_vfio_working_with_qemu/?utm_medium=android_app&utm_source=share

GPU=09:00
GPU_ID="10de 1c82"
GPU_AUDIO="10de 0fb9"
VMID=116

# Remove the framebuffer and console
echo 0 > /sys/class/vtconsole/vtcon0/bind
echo 0 > /sys/class/vtconsole/vtcon1/bind
echo efi-framebuffer.0 > /sys/bus/platform/drivers/efi-framebuffer/unbind

# Unload the Kernel Modules that use the GPU
modprobe -r nvidia_drm
modprobe -r nvidia_modeset
modprobe -r nvidia
modprobe -r snd_hda_intel

# Load the vfio kernel module
modprobe vfio
modprobe vfio_iommu_type1
modprobe vfio-pci

#Assign card to vfio-pci
echo -n "${GPU_ID}" > /sys/bus/pci/drivers/vfio-pci/new_id
echo -n "${GPU_AUDIO}" > /sys/bus/pci/drivers/vfio-pci/new_id

#Start desktop
sudo qm start $VMID

#Wait here until the VM is turned off
while [ "$(qm status $VMID)" != "status: stopped" ] 
do
 sleep 5
done

#Reassign primary graphics card back to host
echo -n "0000:${GPU}.0" > /sys/bus/pci/drivers/vfio-pci/unbind
echo -n "0000:${GPU}.1" > /sys/bus/pci/drivers/vfio-pci/unbind
echo -n "${GPU_ID}" > /sys/bus/pci/drivers/vfio-pci/remove_id
echo -n "${GPU_AUDIO}" > /sys/bus/pci/drivers/vfio-pci/remove_id
rmmod vfio-pci
modprobe nvidia
modprobe nvidia_drm
modprobe nvidia_modeset
modprobe snd_hda_intel
sleep 1
echo -n "0000:${GPU}.0" > /sys/bus/pci/drivers/nvidia/bind
echo -n "0000:${GPU}.1" > /sys/bus/pci/drivers/snd_hda_intel/bind
sleep 1
echo efi-framebuffer.0 > /sys/bus/platform/drivers/efi-framebuffer/bind
echo 1 > /sys/class/vtconsole/vtcon0/bind
echo 1 > /sys/class/vtconsole/vtcon1/bind

With my primary adapter passed through I realized I also want other things passed through, mainly USB. I tried Proxmox’s USB device passthrough options but it doesn’t work well with USB audio (stutters and choppy.) I wanted to pass through my whole USB controller to the VM.

This didn’t work as well as I had planned due to IOMMU groups. A great explanation of IOMMU groups can be found here. I had to figure out which of my USB controllers were in which IOMMU group to see if I could pass the whole thing through or not (some of them were in the same IOMMU group as SATA & network controllers, which I did not want to pass through to the VM.)

Fortunately I was able to discover which USB controllers I could safely pass through first by running lspci to see the device ID, then running find to see which IOMMU group it was in, then checking against lspci to see what other devices were in that group. The whole group comes over together when you pass through to a VM.

First determine the IDs of your USB controllers

lspci | grep USB

01:00.0 USB controller: Advanced Micro Devices, Inc. [AMD] Device 43ba (rev 02)
08:00.0 USB controller: Renesas Technology Corp. uPD720201 USB 3.0 Host Controller (rev 03)
0a:00.3 USB controller: Advanced Micro Devices, Inc. [AMD] Device 145c
43:00.3 USB controller: Advanced Micro Devices, Inc. [AMD] Device 145c

Next get which IOMMU group these devices belong to

find /sys/kernel/iommu_groups/ -type l|sort -h|grep '01:00.0\|08:00.0\|0a:00.3\|43:00.3'

/sys/kernel/iommu_groups/14/devices/0000:01:00.0
/sys/kernel/iommu_groups/15/devices/0000:08:00.0
/sys/kernel/iommu_groups/19/devices/0000:0a:00.3
/sys/kernel/iommu_groups/37/devices/0000:43:00.3

Then see what other devices use the same IOMMU group (the group is the number after /sys/kernel/iommu_groups/)

find /sys/kernel/iommu_groups/ -type l|sort -h | grep '/14\|/15\|/19\|/37'

/sys/kernel/iommu_groups/14/devices/0000:01:00.0
/sys/kernel/iommu_groups/14/devices/0000:01:00.1
/sys/kernel/iommu_groups/14/devices/0000:01:00.2
/sys/kernel/iommu_groups/14/devices/0000:02:00.0
/sys/kernel/iommu_groups/14/devices/0000:02:04.0
/sys/kernel/iommu_groups/14/devices/0000:02:05.0
/sys/kernel/iommu_groups/14/devices/0000:02:06.0
/sys/kernel/iommu_groups/14/devices/0000:02:07.0
/sys/kernel/iommu_groups/14/devices/0000:04:00.0
/sys/kernel/iommu_groups/14/devices/0000:05:00.0
/sys/kernel/iommu_groups/14/devices/0000:06:00.0
/sys/kernel/iommu_groups/15/devices/0000:08:00.0
/sys/kernel/iommu_groups/19/devices/0000:0a:00.3
/sys/kernel/iommu_groups/37/devices/0000:43:00.3

As you can see one of my USB controllers (01:00.0) has a whole bunch of stuff in its IOMMU group, so I don’t want to use it lest I bring all those other things into the VM with it. The other three, though, are isolated in their groups and thus are perfect for passthrough.

In my case I passed through 0a:00.3 & 43:00.3 as 08:00.0 is a PCI card I want passed through to my Windows VM. This passed through about 2/3 of the USB ports on my system to my guest VM.