2017 iMac. Did I expect too much?

[robeddie]

I just re-tested the latest version of LightRoom on a top-spec 2017 iMac 27. Despite having a Radeon Pro 580, Lightroom adjustment brush performance *slows down* when GPU acceleration is *enabled*. It becomes laggy and sluggish. This is 100% reproducible and very consistent. It is actually faster when GPU acceleration *disabled*. That is not a failure of Apple to provide a sufficiently fast GPU -- it is a failure of Adobe to write decent software. The OP issue was with Photoshop but this illustrates that Adobe has serious problems writing efficient code.

Are you using opengl or Metal? Or is there even an option in your version of PS (I know there's one in Premiere)

 

[joema2]

Are you using opengl or Metal? Or is there even an option in your version of PS (I know there's one in Premiere)

It is using whatever graphics API Adobe chose for Lightroom. They do not expose a user-selectable option except to enable/disable GPU acceleration. I think Photoshop is similar. In Premiere you can pick OpenCL or Metal and it doesn't make a significant difference in encode, decode or playback tests I've run, although it might help in specific areas.

It's unfortunate that using GPU acceleration slows down certain Lightroom functions, such as painting with the adjustment brush. It speeds up other functions such as setting white/black point.

The OP could try disabling GPU acceleration in Photoshop; it might speed up his task.