I am trying to understand exactly what this preference does. I had assumed it controlled the number of CPU cores used by the application. But, the User Guide simply says that this is a way to control the impact of the DxO application on the system - you can reduce the load (if you want to run other apps at the same time) by reducing the number of images processed in parallel.
I have been watching what is going on under different settings. I have tested 8 images, 4 images, and 1 image options. In each case, the app uses all the CPU cores. I have an (Intel) iMac Pro with a Xeon W 8-core CPU and a MBP M1 Max with 10 cores (two efficiency, 8 performance). I benchmarked these two systems with the 8/4/1 image settings. Both systems are fastest when processing 4 images. I have a set of 43 RAW images I use for testing - a mixture of Sony A7RM3 and M4, some Olympus E-M5III, and various (older) Canon Digital Rebel images. Here are the timings:
iMac Pro
8 5 minutes, 18 seconds
4 5 minutes, 2 seconds
1 6 minutes, 41 seconds
MBP M1 Max
8 4 minutes, 30 seconds
4 4 minutes, 22 seconds
1 5 minutes, 57 seconds
On both systems, even with 8 images selected, DxO PL5 doesn’t come close to loading these systems anywhere close to 100% - so I doubt this adjustment has any significant effect to the performance of other apps running in parallel - macOS is going to handle the multi-processing. (At least for my hardware - maybe it has more effect for lower end hardware.)
Since I usually run large batches of raw images, I start the process and then leave to have a coffee - I usually don’t have anything else running. I thought perhaps running more images in parallel would help performance.
The other odd thing I have noticed is that this processing is single-threaded somewhere - if you watch the export window as the processing works - with preferences set to (say) 8 images in parallel - images processing and output occurs one image at a time. I had expected that the images would output in batches of 8 images at a time. That doesn’t happen.
I am not at all unhappy with this process, and the speed of processing - I just want to know more about what it actually happening (under the covers!).
David