Virtualizing GPU Access

Posted on 12/02/2018 by Robert Foss

Virtualized GPU access is becoming common in the containerized and virtualized application space. Let's have a look at why and how.

For the past few years a clear trend of containerization of applications and services has emerged. Having processes containerized is beneficial in a number of ways. It both improves portability and strengthens security, and if done properly the performance penalty can be low.

In order to further improve security containers are commonly run in virtualized environments. This provides some new challenges in terms of supporting the accelerated graphics usecase.

OpenGL ES implementation

Currently Collabora and Google are implementing OpenGL ES 2.0 support. OpenGL ES 2.0 is the lowest common denominator for many mobile platforms and as such is a requirement for Virgil3D to be viable on the those platforms.

That is is the motivation for making Virgil3D work on OpenGL ES hosts.

How does this work?

This stack is commonly referred to as Virgil3D, since all of the parts originated from a project with that name.

Collabora - Virtualized OpenGL Stack

There are a few parts to this implementation.

QEMU, virglrenderer and virtio-gpu. They way it works is by letting the guest applications speak unmodified OpenGL to the Mesa. But instead of Mesa handing commands over to the hardware it is channeled through virtio-gpu on the guest to QEMU on the host.

QEMU then receives the raw graphics stack state (Gallium state) and interprets it using virglrenderer from the raw state into an OpenGL form, which can be executed as entirely normal OpenGL on the host machine.

The host OpenGL stack does not even have to be Mesa, and could for example be the proprietary nvidia stack.

Trying it out


First of all, let's have a look at the development environment. When doing graphical development I find it quite helpful to set up a parallel graphics stack in order to not pollute or depend on the stack of the host machine more than we have to.

function add_export_env {
  local VAR="$1"
  local VAL=$(eval echo "\$$VAR")
  if [ "$VAL" ]; then
    VAL=$(concatenate_colon "$@" "$VAL");
    VAL=$(concatenate_colon "$@");
  eval "export $VAR=\"$VAL\""

function prefix_setup {
  local PREFIX="$1"

  add_export_env PATH "$PREFIX/bin"
  add_export_env LD_LIBRARY_PATH "$PREFIX/lib"
  add_export_env PKG_CONFIG_PATH "$PREFIX/lib/pkgconfig/" "$PREFIX/share/pkgconfig/"
  add_export_env MANPATH "$PREFIX/share/man"
  export ACLOCAL_PATH="$PREFIX/share/aclocal"
  mkdir -p "$ACLOCAL_PATH"
  export ACLOCAL="aclocal -I $ACLOCAL_PATH"

function projectshell {
  case "$1" in
    virgl | virglrenderer)
        export ALT_LOCAL="/opt/local/virgl"
        mkdir -p "$ALT_LOCAL"
        prefix_setup "$ALT_LOCAL"

The above snippet is something that I would put in my .bashrc or .zshrc. Don't forget so run source ~/.bashrc or the equivalent after making changes.

To enter the environment I simply type projectshell virgl.

Build libepoxy

libepoxy is a library for managing OpenGL function pointers for you. And it is a dependency of virglrenderer, which we'll get to below.

git clone https://github.com/anholt/libepoxy.git
cd libepoxy
./autogen.sh --prefix=$ALT_LOCAL
make -j$(nproc --ignore=1)
make install

Build virglrenderer

Virgilrenderer is the component that QEMU uses to provide accelerated rendering.
It receives Gallium states from the guest kernel via its virtio-gpu interface, which are then translated into OpenGL on the host. It also translates shaders from the TGSI format used by Gallium into the GLSL format used by OpenGL.

git clone git://anongit.freedesktop.org/virglrenderer
cd virglrenderer
./autogen.sh --prefix=$ALT_LOCAL
make -j$(nproc --ignore=1)
make install

Build libpciaccess

libpciaccess is a library for simplifying accessing devices on the PCI bus.
It is a dependency of Mesa, which we'll get to below.

git clone git://git.freedesktop.org/git/xorg/lib/libpciaccess
cd libpciaccess
./autogen.sh --prefix=$ALT_LOCAL
make -j$(nproc --ignore=1)
make install

Build Mesa

# Fetch dependencies
sudo sed -i 's/\#deb-src/deb-src/' /etc/apt/sources.list
sudo apt update
sudo apt-get build-dep mesa

# Actually build Mesa
git clone https://anongit.freedesktop.org/git/mesa/mesa.git
cd mesa
./configure \
    --prefix=$ALT_LOCAL \
    --enable-driglx-direct \
    --enable-gles1 \
    --enable-gles2 \
    --enable-glx-tls \
    --with-egl-platforms='drm x11 wayland' \
    --with-dri-drivers="i915 i965 nouveau" \
    --with-gallium-drivers="nouveau swrast radeonsi"
make -j$(nproc --ignore=1)
make install

Build QEMU

git clone git://git.qemu.org/qemu.git
cd qemu
./configure \
    --prefix=$ALT_LOCAL \
    --target-list=x86_64-softmmu \
    --enable-kvm \
    --disable-werror \
make -j$(nproc --ignore=1)
make install

Set up a VM

As a guest we're going to use Ubuntu 17.10, but just use the latest release of whatever distro you like. The kernel has have been built with the appropriate virtio-gpu Kconfig options though.

wget http://releases.ubuntu.com/17.10/ubuntu-17.10.1-server-amd64.iso
qemu-img create -f qcow2 ubuntu.qcow2 35G
qemu-system-x86_64 \
    -enable-kvm -M q35 -smp 2 -m 4G \
    -hda ubuntu.qcow2 \
    -net nic,model=virtio \
    -net user,hostfwd=tcp::2222-:22 \
    -vga virtio \
    -display sdl,gl=on \
    -boot d -cdrom ubuntu-17.10.1-desktop-amd64.iso

Run VM

qemu-system-x86_64 \
    -enable-kvm -M q35 -smp 2 -m 4G \
    -hda ubuntu.qcow2 \
    -net nic,model=virtio \
    -net user,hostfwd=tcp::2222-:22 \
    -vga virtio \
    -display sdl,gl=on

Et Voila! Your guest should now have GPU acceleration!


Hopefully this guide will have helped you to build all of the software needed to set up your very own virglrenderer enabled graphics stack.


Original post

Comments (3)

  1. Kieran:
    Feb 13, 2018 at 11:01 AM

    Thanks for the write-up! What kind of overhead does this produce compared to running on host?

    Reply to this comment

    Reply to this comment

    1. Robert Foss:
      Feb 13, 2018 at 04:30 PM

      Hey Kieran!

      That's a good question, I haven't looked into the performance aspect.

      I would think that the performance impact is not too bad. But it would also depend on the application.
      An application that executes more OpenGL calls would see a larger impact.

      Reply to this comment

      Reply to this comment

  2. Ernst Sjöstrand:
    Feb 13, 2018 at 08:29 PM

    Nice! I uploaded packages for Ubuntu with virgilrenderer enabled to my ppa and wrote a few lines about it.... https://www.sabeltand.net/virgl/

    Reply to this comment

    Reply to this comment

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