Ansel will detect OpenCL run-time errors automatically. On detecting an error, it will then reprocess everything on the CPU. While this will slow down processing it should not affect the end result.

Можуть бути різні причини того, чому OpenCL може зазнати невдачі на етапі ініціалізації. OpenCL залежить від вимог до обладнання та від наявності певних драйверів та бібліотек. На додаток, все це повинно відповідати виробнику, моделі та номеру редакції. Якщо щось не підходить (наприклад, ваш графічний драйвер – завантажений як модуль ядра – не відповідає версії вашого libOpenCL.so), підтримка OpenCL, швидше за все, буде недоступна.

In this case, the best thing to do is start Ansel from a console with Ansel -d opencl.

Це дасть додаткові результати налагодження щодо ініціалізації та використання OpenCL. По-перше, якщо ви знайдете рядок, який починається з [opencl_init] FINALLY ..., це повинно сказати вам, чи доступна підтримка OpenCL для вас чи ні. Якщо ініціалізація не вдалася, перегляньте наведені вище повідомлення, щоб знайти щось, що читається як could not be detected (“не вдалося виявити”) або could not be created (“не вдалося створити”). Перевірте, чи є підказка про те, де це не вдалося.

Ось кілька випадків, які спостерігались у минулому:

  • Ansel states that no OpenCL aware graphics card is detected or that the available memory on your GPU is too low and the device is discarded. In that case you might need to buy a new card if you really want OpenCL support.

  • Ansel finds your libOpenCL.so but then tell you that it couldn’t get a platform. NVIDIA drivers will often give error code -1001 in this case. This happens because libOpenCL.so is only a wrapper library. For the real work further vendor-specific libraries need to be loaded. This has failed for some reason. There is a structure of files in /etc/OpenCL on your system that libOpenCL.so consults to find these libraries. See if you can find something fishy in there and try to fix it. Often the required libraries cannot be found by your system’s dynamic loader. Giving full path names might help.

  • Ansel states that a context could not be created. This often indicates a version mismatch between the loaded graphics driver and libOpenCL. Check if you have left-over kernel modules or graphics libraries from an older installation and take appropriate action. When in doubt, perform a clean reinstall of your graphics driver. Sometimes, immediately after a driver update, the loaded kernel driver does not match the newly installed libraries. In this case reboot your system before trying again.

  • Ansel crashes during startup. This can happen if your OpenCL setup is completely broken or if your driver/library contains a severe bug. If you can’t fix it, you can still use Ansel with option --disable-opencl, which will skip the entire OpenCL initialization step.

  • Ansel fails to compile its OpenCL source files at run-time. In this case you will see a number of error messages looking like typical compiler errors. This could indicate an incompatibility between your OpenCL implementation and Ansel’s interpretation of the standard. In that case please raise an issue on github  and we will try to assist. Please also report if you see significant differences between CPU and GPU processing of an image.

A few on-CPU implementations of OpenCL also exist, coming as drivers provided by INTEL or AMD. We have observed that they do not provide any speed gain versus our hand-optimized CPU code. Therefore Ansel simply discards these devices by default. This behavior can be changed by setting the configuration variable opencl_use_cpu_devices (in $HOME/.config/Anselrc) to TRUE.