The device_info loop iterates over the discovered devices and gets
the available and total memory counts. With the CUDA backend (and
possibly others too) this requires creating a GPU context, which,
in case of CUDA, results in a 550 MB VRAM allocation.
For this information to be used in any way, the log verbosity must
be set to LOG_LEVEL_TRACE. If it's not, including in the default
configuration, the contexts get created, memory sizes get queried,
then the log function quietly discards the data.
In certain cases the user may not want to use any GPU resources.
The device_loop iteration is the only place touching the GPU that
cannot be skipped.
Fix by checking the verbosity level and skipping the loop if there
would be no output.
Bartosz Taudul
ba8e0eddfb