UNDERclocking AMD GPU in iMac?

[miretogo]

Hello everyone,

I "upgraded" from a Late 2013 (3.4 GHz i5, NVidia GTX 780m) to a Late 2015 (4.0 GHz i7, AMD R9 m395x) and, like many before, am irritated by high GPU temperatures, which reach up to 105 °C. This phenomenon, which seems to affect all Late 2014/Late2015 owners with AMD R9 m295x/m395x who do intensive gaming on their iMacs, has been thoroughly disccused before on macrumors, e.g. in this extremely long thread: https://forums.macrumors.com/thread...clock-throttling-heat-and-performance.1815601

Since turning up the fans with software such as Macs Fan Control increases the noise and the GPU is still extremely hot sometimes, I would like to UNDERclock the GPU to decrease heat and thereby temperatures and noise.

Since I use Windows 10 via Boot Camp to game, I tried MSI Afterburner, but when I click "Apply" after changing the clock speed, it jumps back to its original setting. I then tried installing AMDs "Overdrive" utility, but after a restart, Windows didn't start anymore and I had to reinstall Windows again via Boot Camp Assistant.

Thus, my questions is: Has anybody successfully UNDERclocked their AMD GPU in their Late 2014/Late 2015 iMac and, if so, how?

 

[miretogo]

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[miretogo]

Instead of underclocking, I enabled Vsync in the games I play to prevent the GPU from rendering more frames than necessary and that, combined with a custom fan curve, keeps the GPU below 80 °C.

 

[dimme]

I want to drag up this old thread because I have the same issue in a 2019 iMac with Radeon Pro Vega 48. I looking for a way to under clock the Gpu to keep it cool. Thanks

 

[miretogo]

Are you bothered by the temperature itself or more my the fan noise? How hot does the GPU get? Also, what do you do with your iMAc that it gets hot? If the task is also very heay on the CPU, then disabling the Turbo Boost will probably reduce the heat output and therefore the noise by a lot. I wrote about that option here:

How to keep iMacs (and Intel Macs in general) cool and quiet

A few days ago, I received a used 2020 iMac with i7 and 5500XT. During intensive tasks such video encoding (under macOS) or gaming (under Windows), the CPU quickly reached 100 °C despite major fan noise. Since both the temperature and the noise were unacceptable to me, I searched for a solution...

forums.macrumors.com

 

[dimme]

I run Xplane 11 occasionally and that is where the problem is. I do use Turbo Boots Switcher and that has helped tremendously with the cpu temperatures. So my issue is with the radeon pro Vega 48 GPU it will run at 95C+. to see that is just too hot. I only use Xplane on the weekends, for my normal task Photoshop, Lightroom etc the system is great. If the solution is windows only that could also work, not ideal but I'll take it.

 

[miretogo]

I also run X-Plane 11 (on an 2020 iMac with 5500XT).

What's your average frame rate? You can enable vertical synchronisation ("vsync") in X-Plane's graphics settings and then your iMac will only render 30 or 60 fps and not render superfluous frames (that wouldn't be displayed anyway because the display refreshes in fixed 60 Hertz intervals, i.e. every 1/60 seconds = 16.6 milliseconds).

Also, have you enabled the Metal option in the graphics settings? As you may know, it is much more efficient than the default (OpenGL). It almost doubled the frame rate for me. Combined with vsync, the iMac then has to work less intensively. You find infos about that here: https://x-plane.helpscoutdocs.com/article/100-flying-with-vulkan-metal

If that is still not enough, you can install Macs Fan Control and enable a custom fan setting. For example, you can set it so that it reaches full speed at a GPU temperature of 80 degrees Celsius. You can download it for free here: https://crystalidea.com/macs-fan-control/download

 

[dimme]

Thank you for the reply, yes I am using metal and vsync. Xplane runs about 55 FPS. At first I was having a issue with the machine just sitting down in mid flight. (from over heating) I found a program called turbo booster switcher which allows me to disable turbo boost. And that stopped the CPU's from over heating. So now I am looking at the GPU. The iMac has been a wonderful machine except for XPlane. In Xplane it just gets too hot and the fans don't keep up with the heat.

 

[miretogo]

How do you measure the temperatures? How do you measure the frame rate?

I recommend the following:
1) Use my graphics settings (see attached screenshot). This disables effects which are very computionally intensive but bring little image quality.
2) If it your GPU still gets too hot, use Macs Fan Control to enable a custom fan setting while playing X-Plane (for example, reaching the fan its maximum if the GPU reaches 80 degrees Celsius).
3) If the GPU is still getting too hot, then install X-Plane in Windows and use one of the available tools to limit the frame rate to a certain amount that is lower then the frame rate your are getting without vsync (for example, 30 FPS is very popular in the flight sim community).

Additional infos:
A) Please look at the small screenshot with the numbers. If the "gpu time" is higher than the "cpu time", then the CPU must wait for the GPU - and vice versa. Thus, if your GPU is overheating, change X-Plane's graphics settings so that the GPU must wait for the CPU. This way, it has some time to "cool off" during every frame.
B) I may be wrong, it seems to me that the vsync option is not working correctly in X-Plane 11.50 right now. For example, when I am in a situation where I get 73 FPS without vsync and then enable vsync, I suddenly get about 37 FPS instead of the expected 60 FPS.

 

[dimme]

I am using TG Pro to monitor my temperature. My settings are similar to yours. TG pro does have the ability to set up a custom fan curve and I can target which temperature reading to activate the fan. I think that will be the next step. Also I think I need to learn more about the cup & gpu time data in the frame rate window. Thanks again fo the help.