macOS: Blender doesn't utilize GPU for background rendering if Metal device type preference is set via script #114326

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Ingo Clemens · 2023-10-31T14:34:17+01:00

Ingo Clemens commented

2023-10-31 14:34:17 +01:00

System Information
Operating system: macOS-13.5.2-arm64-arm-64bit 64 Bits
Graphics card: Metal API Apple M1 Max 1.2

Blender Version
Broken: version: 4.0.0 Beta, branch: blender-v4.0-release, commit date: 2023-10-30 23:38, hash: b27ff093caa0
Worked: before 3.6.1

Short description of error
When the preference setting System > Cycles Render Devices > Metal is set via the python command
bpy.context.preferences.addons['cycles'].preferences.compute_device_type = 'METAL'
the background rendering doesn't use the GPU but only the CPU, which results in much slower render times.

The python command definitely sets the preferences (of course along with saving the prefs).

When rendering from within the open Blender session the preference setting is respected.

When setting the preference setting manually and then starting the background rendering, the GPU is used as expected.

Exact steps for others to reproduce the error

Start Blender without any preferences, as it just has been downloaded.
Execute:

import bpy
bpy.context.preferences.addons['cycles'].preferences.compute_device_type = 'METAL'
bpy.ops.wm.save_userpref()

Close Blender.
Open the Terminal application and run:
/Applications/Blender.app/Contents/MacOS/Blender --background /PATH_TO_PROJECT_FOLDER/renderTest/test.blend -a

The rendering consists of two frames of which each should only take about half a minute or less (without kernel processing).

The project folder to test with is attached.

**System Information** Operating system: macOS-13.5.2-arm64-arm-64bit 64 Bits Graphics card: Metal API Apple M1 Max 1.2 **Blender Version** Broken: version: 4.0.0 Beta, branch: blender-v4.0-release, commit date: 2023-10-30 23:38, hash: `b27ff093caa0` Worked: before 3.6.1 **Short description of error** When the preference setting System > Cycles Render Devices > Metal is set via the python command `bpy.context.preferences.addons['cycles'].preferences.compute_device_type = 'METAL'` the background rendering doesn't use the GPU but only the CPU, which results in much slower render times. The python command definitely sets the preferences (of course along with saving the prefs). When rendering from within the open Blender session the preference setting is respected. When setting the preference setting manually and then starting the background rendering, the GPU is used as expected. **Exact steps for others to reproduce the error** 1. Start Blender without any preferences, as it just has been downloaded. 2. Execute: ``` import bpy bpy.context.preferences.addons['cycles'].preferences.compute_device_type = 'METAL' bpy.ops.wm.save_userpref() ``` 3. Close Blender. 4. Open the Terminal application and run: `/Applications/Blender.app/Contents/MacOS/Blender --background /PATH_TO_PROJECT_FOLDER/renderTest/test.blend -a` The rendering consists of two frames of which each should only take about half a minute or less (without kernel processing). The project folder to test with is attached.

renderTest.zip

301 KiB

Ingo Clemens added the

labels 2023-10-31 14:34:18 +01:00

Douglas Paul commented

2023-11-03 02:03:16 +01:00

I can confirm the described behavior as of the latest 4.0.0 Beta build.

After verifying it using the exact steps originally described, I experimented a bit and found a slightly simpler way to demonstrates the issue. It doesn't require re-launching Blender or saving the preferences to disk.

Launch Blender with the factory settings, but opening test.blend:

/path/to/Blender --factory-startup /path/to/renderTest/test.blend

Switch to the "Scripting" workspace, and in the Python terminal run:

C.preferences.addons['cycles'].preferences.compute_device_type = 'METAL'

In the main menu, click Render > Render Animation (or use the keyboard shortcut) to render the animation. Observe that the status line does not end with "(Using optimized kernels)", and the render takes significantly longer than it would if it were actually using the Metal backend. Close the render window.
Open the Blender preferences, switch to the "System" tab (and observe that the device is indeed set to Metal), and then close the preferences again (without having changed or saved anything).
Do Render > Render Animation again, and note that this time it uses Metal. (The status line ends in "(Using optimized kernels)", and assuming no kernels needed to be compiled, the render is much faster.)

I can confirm the described behavior as of the latest 4.0.0 Beta build. After verifying it using the exact steps originally described, I experimented a bit and found a slightly simpler way to demonstrates the issue. It doesn't require re-launching Blender or saving the preferences to disk. 1. Launch Blender with the factory settings, but opening `test.blend`: ``` /path/to/Blender --factory-startup /path/to/renderTest/test.blend ``` 2. Switch to the "Scripting" workspace, and in the Python terminal run: ``` C.preferences.addons['cycles'].preferences.compute_device_type = 'METAL' ``` 3. In the main menu, click Render > Render Animation (or use the keyboard shortcut) to render the animation. Observe that the status line does _not_ end with "(Using optimized kernels)", and the render takes significantly longer than it would if it were actually using the Metal backend. Close the render window. 4. Open the Blender preferences, switch to the "System" tab (and observe that the device is indeed set to Metal), and then close the preferences again (without having changed or saved anything). 5. Do Render > Render Animation again, and note that this time it uses Metal. (The status line ends in "(Using optimized kernels)", and assuming no kernels needed to be compiled, the render is much faster.)

Jesse Yurkovich commented

2023-11-03 02:38:43 +01:00

Setting the appropriate render devices from Python is a bit more involved. The full sequence is typically something like the following:

# Set the device type
C.preferences.addons['cycles'].preferences.compute_device_type = 'METAL'

# Refresh the list of devices
C.preferences.addons['cycles'].preferences.get_devices()

# Actually "use" the devices you want to...
# You can check .devices[...].type to find one that != "CPU" ... in this case I'm assuming the M1 GPU is device[1]
C.preferences.addons['cycles'].preferences.devices[1].use = True

So you must not only set the compute_device_type but you must also explicitly select the devices to "use".

Setting the appropriate render devices from Python is a bit more involved. The full sequence is typically something like the following: ``` # Set the device type C.preferences.addons['cycles'].preferences.compute_device_type = 'METAL' # Refresh the list of devices C.preferences.addons['cycles'].preferences.get_devices() # Actually "use" the devices you want to... # You can check .devices[...].type to find one that != "CPU" ... in this case I'm assuming the M1 GPU is device[1] C.preferences.addons['cycles'].preferences.devices[1].use = True ``` So you must not only set the `compute_device_type` but you must also explicitly select the devices to "use".

Douglas Paul commented

2023-11-03 02:54:24 +01:00

@braverabbit If you want to insulate your code from device order changes/inconsistency, you could loop over all of the devices and set use automatically based on type:

for device in C.preferences.addons['cycles'].preferences.devices:
  device.use = (device.type != 'CPU')

@braverabbit If you want to insulate your code from device order changes/inconsistency, you could loop over all of the devices and set `use` automatically based on `type`: ``` for device in C.preferences.addons['cycles'].preferences.devices: device.use = (device.type != 'CPU') ```

Pratik Borhade added

Status

Needs Information from User

and removed

Status

Needs Triage

labels 2023-11-03 05:00:38 +01:00

Raimund Klink commented

2023-11-03 09:16:00 +01:00

What about --cycles-device METAL? Does it work as expected?
https://docs.blender.org/manual/en/latest/advanced/command_line/render.html#cycles

What about `--cycles-device METAL`? Does it work as expected? https://docs.blender.org/manual/en/latest/advanced/command_line/render.html#cycles

Ingo Clemens commented

2023-11-03 11:26:28 +01:00

Thanks for the fast replies everyone.
I assumed that something else was missing, since it didn't work with a single preference switch. Thanks for finding it.

It appears that even only using:

C.preferences.addons['cycles'].preferences.compute_device_type = 'METAL'
C.preferences.addons['cycles'].preferences.get_devices()
bpy.ops.wm.save_userpref()

works also for background rendering. So far it wasn't necessary to also set use for the device. Might be saver though? I don't know.

Using the render flags --cycles-device METAL as in

Blender --background /PATH_TO_PROJECT_FOLDER/renderTest/test.blend -a -- --cycles-device METAL

also works as expected but of course is only temporary for the rendering and not changing any preference settings.

The interesting part is that only using the simple (and now obsolete) code mentioned in my first post

import bpy
bpy.context.preferences.addons['cycles'].preferences.compute_device_type = 'METAL'
bpy.ops.wm.save_userpref()

worked fine for several versions of Blender until it ceased to work without changing anything of the setup. Basically it stopped working mid project. On one machine about two weeks before it stopped working on another one. I am not sure which Blender version it was but probably 3.4 or 3.5.
Interesting how these things have a life of their own.

Thanks for the fast replies everyone. I assumed that something else was missing, since it didn't work with a single preference switch. Thanks for finding it. It appears that even only using: ``` C.preferences.addons['cycles'].preferences.compute_device_type = 'METAL' C.preferences.addons['cycles'].preferences.get_devices() bpy.ops.wm.save_userpref() ``` works also for background rendering. So far it wasn't necessary to also set `use` for the device. Might be saver though? I don't know. Using the render flags `--cycles-device METAL` as in `Blender --background /PATH_TO_PROJECT_FOLDER/renderTest/test.blend -a -- --cycles-device METAL` also works as expected but of course is only temporary for the rendering and not changing any preference settings. The interesting part is that only using the simple (and now obsolete) code mentioned in my first post ``` import bpy bpy.context.preferences.addons['cycles'].preferences.compute_device_type = 'METAL' bpy.ops.wm.save_userpref() ``` worked fine for several versions of Blender until it ceased to work without changing anything of the setup. Basically it stopped working mid project. On one machine about two weeks before it stopped working on another one. I am not sure which Blender version it was but probably 3.4 or 3.5. Interesting how these things have a life of their own.

Raimund Klink commented

2023-11-03 11:45:39 +01:00

So, it was a user issue, right? Case closed then :)