By default Lightroom will have the GPU on, unless it encounters an error with the GPU. The GPU really needs to be good, or Lightroom will actually be slower to use. Sometimes you can have crashes on startup, even with the 6.01 update so here’s a way to turn off the GPU without opening Lightroom.
Restart your machine. This is essential (especially on Mac), so that the preferences are not stored in memory when we edit them-or they will just be overwritten. When I was working on this, I hadn’t, and everytime Lightroom reopened it would revert the settings back to before I’d saved.
Find the Lightroom preferences file. On Mac, hold down Option and then select Library (hidden without the Option key) from the Go menu. Open the Preferences folder and search for com.adobe.Lightroom6.plist. On PC go to C:\Users\[user name]\AppData\Roaming\Adobe\Lightroom\Preferences\Lightroom 6 Preferences.agprefs where [user name] is your login name.
Open the file in a text editor. Don’t use Word, etc, use Text Edit or Notepad.
Now on the line below this, change true to false and save.
It should now look like this:
Now start Lightroom. The GPU will be off. Hopefully if the GPU is your crash issue, this should let you start Lightroom.
Note: I did read similar suggestion on the Adobe forums last week, but I couldn’t find it in search, so I manually went through the preferences file to find the right preference for the GPU. During testing I noticed the rewriting on Lightroom startup and remembered that the preferences are now stored in memory once read, hence testing with a restart.