Cycles rendering on 2017 iMac with AMD 580 using Blender 3.1

I have been following the development of Blender and Metal over the past few months and was excited to see that with Mac OS release of 12.3 that Metal would be supported with older Intel Macs with AMD graphics cards. Before I installed 12.3 on. my 2017 5K iMac I ran some benchmarks on a simple Blender scene and some rather strange results.

On OS 12.2.2
Blender 3.0. 45.55 seconds
Blender 3.1b 49.18 seconds
Blender 3.1 today release 49.88 seconds

OS 12.3
Blender 3.1 today release without GPU support 52.23
Blender 3.1 today release with RX580 GPU support 2.15.45

The strange thing is not only is it significantly slower using the Metal but when a start a render I just a spinning lollypop and under force quit it says blender is not responding. If I wait long enough the window will open and the render will complete and reflect to actual total time even including window not open time.

Bottom line here Apple and Blender still have some work to do to implement Metal in Blender.

Mine does the same thing on iMac Pro and MacBook 16 inch, but after the 1st render for some reason it renders quick. its just the initial render that the icon spins and then final renders. weird

A render that im doing with just 100 samples with Cycles CPU takes over 2 min 32 seconds with cycles using GPU is taking 39 seconds.

Thanks Dan,

I reopened Blender and the same file again and just like you said the was 30 sec as compared with around 50 with just the CPU render. A welcome improvement. I am debating getting a base Mac Studio with 24 GPU cores which should be much faster. I dont do a ton of stuff in Blender but a Metal GPU render will be great for little I do. Thanks for the taking the time to reply.