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BC-250 ACE Queues

Lets games on the AMD BC-250 use its dedicated compute queues (async compute). Games split a frame into graphics work and compute work (lighting, particles, post-processing, upscaling). With a compute queue of its own, the compute work runs beside the graphics work on shader cores that would otherwise wait.

The BC-250's GPU has these queues (the ACE, Asynchronous Compute Engines), but the stock Mesa driver keeps them closed: on this chip its compute dispatches came out wrong. The app builds a patched RADV (Mesa's Vulkan driver) that opens them and runs their dispatches in a mode that works on this chip. That driver is installed beside the system Mesa, which is never changed. Games use it only when you say so, and only after the app's test passed on the running kernel.

The upstream project measured +21 to +25 % in Cyberpunk 2077 (1440p, Medium, with the 40-CU unlock). The gain depends on the game: only games that use async compute gain anything.

Changes the board

The app installs a GPU driver and can make it the driver of every app. It is software-only and can be undone: Remove takes the driver out again, and the system Mesa stays as it was. Read this chapter first.

Before you start

  • A BC-250 on Bazzite (the app builds for the Fedora version Bazzite is based on).
  • About 1 GB free in your home folder during a build, and an internet connection.
  • podman, which Bazzite ships.

Using it

Install the app from the BC250 Bazzite Suite portal, where it is under Gaming, or from a clone or release folder, as your own user (not with sudo):

./install.sh                         # app menu entry and Desktop icon
./install.sh --no-desktop-shortcut   # app menu entry only

Installing the app changes nothing on the board. Open BC-250 ACE Queues and go through the four steps.

  1. Build. Builds the patched RADV for the Mesa version your system has, as your own user, in a Fedora container. It downloads the Mesa source and the build tools (several hundred MB) and takes 20 to 40 minutes. Nothing on the system changes.
  2. Install. Copies the driver to /usr/local/lib/bc250-ace-queues (asks for your password). Nothing uses it yet.
  3. Test. Runs the ACE queue test with the installed driver, about a minute. Games only get the driver once the test has passed on the running kernel.
  4. Use. Per game, or for every app:

    • Per game: Copy launch options and paste them into the game's Properties → Launch options in Steam:

      /usr/local/bin/bc250-ace-queues-run %command%

      When the test has not passed on the running kernel (after a kernel update, or with a new driver), the game starts with the system Mesa instead, and ~/.local/state/bc250-ace-queues/run.log says why. - All apps: every app uses the patched driver, the desktop included, without launch options. It applies after you log out and back in. Flatpak apps keep their own driver.

The status next to the title sums it up: Not built, Not installed, Test needed, Ready, Test failed or On for all apps.

The test

The test runs the same work on every compute queue at once: a buffer fill, a buffer copy, a copy into an image and back (the driver's own copy shaders, where the bug dropped rows), and a compute dispatch whose last workgroup is a partial one. It compares every result word for word, then closes the queues and opens them again, ten times. It also checks the kernel log for GPU ring timeouts and resets during the test.

A failed test means: don't use the driver on this kernel. Its output is in ~/.local/state/bc250-ace-queues/test.log.

Why a test per kernel

The upstream fix also patches the kernel, to repair how the compute queues are set up and torn down. Bazzite's kernel is not patched. The Bazzite port of the fix runs without the kernel patches on Bazzite's kernels, so this app does too, but checks each kernel with its test before games may use the driver.

When the kernel or Mesa changes

  • A kernel update: games with the launch options start with the system Mesa until you run the test again. With All apps on, a check at boot (before anyone logs in) switches it off; the window then says so. Run the test, then switch it on again.
  • A Mesa update: the installed driver keeps working. The Build step says when the system has a newer Mesa; build and install again to keep up with it, then run the test.

If something goes wrong

  • A game does not start, or shows corruption: take the launch options out of the game. If the test passed, please report it with the game and run.log.

  • The desktop does not come back after switching on All apps: press Ctrl+Alt+F3, log in and run:

    sudo rm /etc/environment.d/90-bc250-ace-queues.conf
sudo reboot

  • Remove in the window switches All apps off and removes the driver. Take the launch options out of your games first: without the driver they do not start.

From a terminal

The window runs bc250-ace-queues.sh in the app's folder (/opt/bc250-ace-queues). The same steps by hand:

/opt/bc250-ace-queues/bc250-ace-queues.sh --status
/opt/bc250-ace-queues/bc250-ace-queues.sh --build            # as your own user
sudo /opt/bc250-ace-queues/bc250-ace-queues.sh --install-driver
/opt/bc250-ace-queues/bc250-ace-queues.sh --test
sudo /opt/bc250-ace-queues/bc250-ace-queues.sh --all-apps on # or off
sudo /opt/bc250-ace-queues/bc250-ace-queues.sh --remove-driver

What goes where

Where What
/opt/bc250-ace-queues the app (root-owned)
~/.cache/bc250-ace-queues the Mesa source and your build; removed when you uninstall the app
~/.local/state/bc250-ace-queues test results, the test log and run.log
/usr/local/lib/bc250-ace-queues the installed driver and the ACE queue test
/usr/local/bin/bc250-ace-queues-run the launch options wrapper
/etc/environment.d/90-bc250-ace-queues.conf, /etc/profile.d/90-bc250-ace-queues.sh only with All apps on
bc250-ace-queues-guard.service only with All apps on: the check at boot

On Bazzite /usr/local is /var/usrlocal: writable, and kept across image updates, so the driver needs no layering and no reboot.

Uninstalling the app (./install.sh --uninstall) removes the app and the build, and leaves an installed driver as it is; remove that first with Remove. --purge also removes the settings and the test results.

How it is built

  • Mesa source: the release from archive.mesa3d.org that matches the system's Mesa version, checked against its signature with the keys of the Mesa release maintainers (from Mesa's own source, bundled with the app).
  • The patch (mesa/gfx1013-ace-queue.patch, one file, src/amd/common/ac_gpu_info.c): opens the compute queue on GFX1013 and gives it the async compute workaround RADV already has for the Iceland and Tonga GPUs. That workaround runs compute dispatches in thread-dimension mode instead of threadgroup-dimension mode.
  • The build: RADV alone (no OpenGL, no LLVM), with the prefix /usr/local/lib/bc250-ace-queues, in a registry.fedoraproject.org/fedora container of your Bazzite's Fedora version, so it links against the same libraries. The driver's game profiles (drirc) point at the system's.

Credits