The most recent updated today.
Thanks for the link to that mammoth discussion.
It seems that my observations were correct. Preview rendering is slower with GPU.
It was the slow 1:1 previews that I wanted to speed up.
I have just got a new card a AMD R7 250. It is no better than my old AMD 5450.
I wish I had read this discussion earlier.
I did search for GPU support, but this discussion did not come up
I did not really check the other functions that GPU speeds up.
Perhaps I should put the new card back in.
Now that I have a better idea of what using the GPU does, I did some tests.
I used the clone tool with a circle of 100 on a Full view of a 5184 x 3456 Canon 7D file.
With GPU the sliders and moving the clone is really notchy, but without GPU really smooth.
Redraw time seems to be the same.
I have a modest AMD 5450 Video and not too modest i7 quad 2.93 and 16GB of ram with a Samsung SSD as preview !:1 cache.
Building previews can be the same with GPU on or off, but most times almost twice as long.
It might be useful for the prefs to have a list of what GPU does and for users to choose the most beneficial to them.
It seems to me from my tests that using no GPU is actually better for my system as it seems to use fewer resources.
I took some screen grabs with GPU on and off in conjunction with a utility which shows the CPU activity and temperature.
The size feather and opacity settings were the same, even thought it does not show in both grabs.
GPU on is on the left.
Not amazingly scientific, but it might be useful.
The GPU does't accelerate import/export or building previews. The GPU only accelerates the interactive adjustments in the Develop module: Adobe Photoshop Lightroom Help | Lightroom Graphics Processor Acceleration (GPU) Troubleshooting & FAQ
The 5040 is an older card and not on our recommended list.
Thanks for your reply.
Yes that does seem to be the case.
Well from my experience, GPU on has some not so good effects on building the preview in the Develop module.
It takes about twice as long to make a 1:1 in Develop with GPU on.
I have the 5450 card and that does now work with the new beta driver, but as you say it is quite old, Even so it should help a little, but it actually seems to hinder
I have just bought a newer R7 250, but have now decided to not get too involved with GPU stuff, As far as I can see, it is still work in progress.
For completeness sake I decided to try the new AMD R7 250 video card.
It seems that the lens correction transform controls are much better with GPU.
The exposure controls seem a mite more responsive.
The situation with moving the 100px clone source is much the same.
Very notchy. and not interactive, in that the destination does not update till the source stops moving, but the redraw is pretty well instant.
With GPU off, moving the source is smooth and interactive, but not as instant to complete, when the source stops moving.
Viewing at 1:1 takes longer with GPU on, sometimes almost twice as long.
As I said earlier, work in progress, so I will return the video card and keep to the old one.