Experimenting to assign the exclusive use of CPU Threads to FreeCAD

September 2025

The main idea is to let FreeCAD use processor threads exclusively for it, this will improve performance in slightly large assemblies etc etc. I'm not an expert - I like to experiment - so use this at your risk.

I use Void Linux and the package we need is cpuset , I don't know about it in other distributions but I assume it must be very similar.

juanma@VOID:~$ xbps-query -Rs cpuset
[*] cpuset-1.6.2_2 Wrapper to make kernel cpusets facilities easier to use


juanma@VOID:~$ xbps-query -Rs freecad
[*] freecad-1.0.2_3       General purpose 3D CAD modeler

Process - How to !

We start FreeCAD and look for what the process is runnig.

juanma@VOID:~$ pgrep -f FreeCAD
16636

or using 'btop'

I have an AMD Ryzen 5 5600X with 6 cores and 12 threads and for this example I am going to assign 2 exclusive threads , 6 and 11 - why ? I want two threads and I have chosen them at random. It could be more than 2 but this is a test.

To view cset status and processes and threads:

juanma@VOID:~$ cset shield -s -v 
cset: **> shielding not active on system 

We reserve the threads:

juanma@VOID:~$ sudo cset shield --cpu 6,11 
Password: 
cset: --> activating shielding: cset: moving 1455 tasks from root into system cpuset... 
[======== cset: "system" cpuset of CPUSPEC(0-5,7-10) with 1455 tasks running 
cset: "user" cpuset of CPUSPEC(6,11) with 0 tasks running 

We assign the FreeCAD pid

juanma@VOID:~$ sudo cset shield --shield --pid 16636 
cset: --> shielding following pidspec: 16636 cset: done 

We review the status to verify if they have been assigned correctly:

juanma@VOID:~$ cset shield -s -v 

cset: "user" cpuset of CPUSPEC(6,11) with 1 task running 

USER PID PPID SPPR TASK NAME 
-------- ----- ----- ------- 
juanma 16636 1 Soth /usr/lib/freecad/bin/FreeCAD - --single-instance 
cset: done 

Seeing it in btop - for example doing a render or something that consumes a lot - we have:

Works OK!!!

To reverse all this we could unassign the pid to the threads or there is also an option to reset everything - this can be investigated and experimented with - but in this example I do a reset.

juanma@VOID:~$ sudo cset shield --reset 
Password: 
cset: --> deactivating/resetting shielding cset: moving 1 tasks from "/user" user set to root set... 
cset: moving 1435 tasks from "/system" system set to root set... 
[======== cset: deleting "/user" and "/system" sets cset: done 

we review the status :

juanma@VOID:~$ cset shield -s -v 
cset: **> shielding not active on system 

Everything ok.

Note: I have not made any benchmarks or anything like that , this is for fun and experimenting !!!

template download

---

This is the script , modify it if you need to.

  
    
#!/usr/bin/env bash

# This program tries to asign exclusive use of CPU Threads to FREECAD
# to allow the program to runs smootly

# This program needs to use 'sudo or doas' for certan tasks

# JuanMa <numblinux@gmail.com>
# https://linuxnauta.com
# 2025
set -m

VERSION='0.1'
PROGRAM='FreeCAD' # this is the name in Void Linux
CORES=(6 11)


    #If we run the script with unset as parameter we reset all and exit
    if [ "$1" == "unset" ]; then
        sudo cset shield --reset
        cset shield -s -v
        exit
    fi

    #Run FreeCAD
    nohup FreeCAD &

    sleep 2000 &

    pid=$(pgrep -f "$PROGRAM")

    #Is running ?
    if [ -z "${pid}" ]; then
        echo "${PROGRAM} is not running ... so ... exit"
        exit
    else
        echo "The PID of $1 is: $pid"
    fi


    echo "trying to set exclusive use of cores  ${CORES[@]}"

    echo -e "\n"

    cset shield -s -v


    for value in ${CORES[@]}
        do
            CORESTXT=${CORESTXT}"${value},"
        done

    # remove the last ","
    CORESTXT=${CORESTXT:0:-1}

    echo CORESTXT

    sudo cset shield --cpu ${CORESTXT} --kthread
    sudo cset shield --shield --pid ${pid}

    cset shield -s -v


    echo "-----------------------------------------------------------"
    echo " DONT FORGET to RUN  'sudo cset shield --reset' to clear all"
    echo "-----------------------------------------------------------"
    echo " or run the script again with unset as parameter 'sudo freecad-cset unset"
    echo "-----------------------------------------------------------"

    exit

---

September 2025