New dt OpenCL features for 5.8

hannoschwalm · August 10, 2026, 10:24am

There is a bunch of OpenCL related stuff that has already landed in darktable master so people using nightly appimages might be interested and test using -d pipe -d opencl …

The OpenCL code path got an internal faster tiling mode for some modules, people on smaller cards developing large images will notice performance gains.
You can now disable OpenCL processing for specific modules. This could be relevant if some module doesn’t run on some hardware (currently there is no such known issue) but more relevant on systems with slow OpenCL hardware but potent CPUs. If you want to explore or tune your system you have to edit your darktablerc file; there will be a line ending with _no_cl for every detected device. Add a comma-separated-list list of modules you want to do on CPU like demosaic,diffuse to that conf entry and restart dt. (Note: we could easily add toggles to modules or add a preference option but that would be clobbering UI so a no for now)
There is a new cli option --opencl-migrate. If used, all OpenCL memory allocations will work slightly different, runtime allocations checks will be much safer but likely with a performace penalty.
I am very interested
a) In performance results comparing this option being on vs off with otherwise unchanged options.
b) If you suspect your systems is unstable or crashes because of OpenCL a logs using above option might help further.

@Qor pinging

Phemisters · August 10, 2026, 11:53am

When I documented this (here) I said the option was a line ending nocl (no space) because to me that looked like what it should be: opencl.c

Is it really no_cl?

hannoschwalm · August 10, 2026, 12:11pm

Arrgh, you are fully right _nocl

zurdo · August 10, 2026, 1:38pm

Just in case these results on iMas intel may help
-d opencl & --opencl-migrate.txt (23.8 KB)
. The log of: -d pipe -d OpenCL with a NEF image that I use for testing.

When using --OpenCL-migrate, darktable opens in lightable and shows images in collections but, when trying to open an image dt crash. The log is at the end of this file.

Eddie_Lambrechts · August 10, 2026, 3:50pm

This has to be done per workspace instance of darktablerc when using multiple workspaces. Can this be changed to the common darktablerc?

Great feature, thanks.

kofa · August 10, 2026, 3:57pm

Export is enough to test, right? I could try a few small and large raw files.

hannoschwalm · August 10, 2026, 3:59pm

Yes - export would be good/enough

hannoschwalm · August 10, 2026, 4:06pm

Thanks for reporting this. I haven’t seen dt crashing because of --opencl-migrate, the underlying OpenCL function is standard 1.2 so it should run on apples too.
Please open a github issue, and if possible provide raw&xmp so we might get more feedback on this

zurdo · August 10, 2026, 7:26pm

Issue open but I could not (or I did not find the correct way) add the raw&xmp

mino · August 10, 2026, 7:30pm

drag and drop should work? Maybe you have to wrap 'em in a .zip.

sugarbravo · August 11, 2026, 6:06pm

Here is running on Debian Sid, Arc B580 GPU.

arc_b580.txt (15.9 KB)
arc_b580_oclmigrate.txt (15.9 KB)

Macchiato17 · August 11, 2026, 8:31pm

Thanks for all your effort @hannoschwalm to make processing faster and faster and the GUI more and more responsive in darkroom. I really appreciate your ongoing work and I’m always thrilled, whenever another OpenCL related commit shows up in master

I checked with [20679847], not much of a difference between normal and --opencl-migrate, some 1-2% slower with the switch set. Please see the logs (I used @Qor’s example RAWs and darktable-cli --core as written on the darktable.info performance testing page for testing this).

24MP_gpu-26.27.39122.11_dt-20679847.txt (15.2 KB)
24MP_gpu-26.27.39122.11_dt-20679847_migrate.txt (15.2 KB)
61MP_gpu-26.27.39122.11_dt-20679847.txt (15.5 KB)
61MP_gpu-26.27.39122.11_dt-20679847_migrate.txt (15.5 KB)

If you need a different test, just drop a line