this post was submitted on 17 Jun 2023
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Steam Deck
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That's actually a misconception, though one that was often propagated so it stuck, unfortunately.
The Steam Deck will dynamically allocate video memory - way below 4GBs, or even larger than 4GBs, regardless of what you set as the UMA framebuffer setting. And it will change this allocation in real time, during each frame, as it monitors memory pressure.
The UMA buffer will indeed give a default "the GPU would like to report that 4GBs of memory are mapped to itself when the driver loads" but the CPU can (and will!) immediately ignore that as soon as needed.
Don't believe me? If you got 15 minutes to do a little experiment, try setting it at 256MB. 256MB for a device running modern games? No way! It won't get past the loading screen, right? Well, it will, and the performance will be quite literally identical to setting it at 4GB.
Addendum: some games give warnings of "Your system do not meet the minimum requirements of VRAM" when running on systems with APUs, in that particular case, setting a large UMA buffer will probably work to bypass the warning... But again, performance is similar.
Theoretically I agree with you, but I finally broke down and changed mine due to some instability and I haven’t had a problem since.
It’s completely possible that’s just placebo since my understanding of how it should work says you are right.
Oh, I'm not claiming you'll get any problems - you won't, don't worry, you can set it or leave it be without issues. You don't have to revert your setting, sorry if my comment gave that impression.
But it will not give you any benefits, really. It's like setting a different wallpaper - you can do it, it won't harm anything, but it won't actually improve games.
My understanding on the advantage for the VRAM change is that RAM gets priority over VRAM. If the systems needs more RAM, it will allocate the VRAM to RAM, and then reallocate back to VRAM, over and over. Increasing the minimum VRAM both keeps the VRAM from dropping below 4GB during high RAM demand and reduces the system swapping RAM between VRAM and RAM. That swapping back and forth can cause stuttering, which is the main thing the VRAM change is trying to fix.
I don't fault your logic, but unfortunately (and I really do mean unfortunately) that's not the case. The CPU gets absolute priority and can quickly take memory for itself.
Perhaps on other APU architectures that's not the case, I wouldn't know, but with the Steam Deck the CPU is always the maximum priority for memory allocation.
@kadu @Fubarberry FWIW the author of cryoutilities has done benchmarks and figured that increasing the default on the Deck does improve performance in some games slightly. He claims that introducing the swapfile also mitigates any potential disadvantages.
He did publish benchmarks, and he did isolate the VRAM change in at least one video I'm aware of... But he only showed very few games, with an improvement that's measured as less than 5% which is well within the margin of error.
Another YouTuber tried a round of CryoUtilities + 4GBs on over 20 games, and while he did get a 10% improvement in some (and we can't know which settings actually mattered as all of them were enabled) he also got a 10% decrease in others.
The point is though, none of this actually matters - because this setting can't possibly impact performance. It wasn't designed for this purpose, and the changes it does make can't affect how the APU will actually allocate memory. Do note that I'm talking about the 4GBs of VRAM thing though, messing with the swap file size and other similar things can indeed have a positive or negative impact on performance.
If you watch Cryo's specific game videos, he usually does a specific isolated 4GB VRAM tweak in every game. Often it does nothing, but sometimes it has a minor fps improvement or reduces stutter.
I've also seen other YouTubers run a list of games through cryoutilities (whole suite of changes, not just the VRAM tweak), and it definitely helps more than it hurts. Not huge gains, but it's free and relatively easy to do. Outside of a few games like RDR2 that have serious drawbacks it's usually worth it imo.
Yeah, most people set it larger for desktop mode or windows use, where the drivers don't auto allocate vram. Although as you said it seems many think it affects game mode which it doesn't.