disabling BAR causes a decrease in VRAM appetite from 0.5-1 GB… is this a BUG or a normal situation?
We all struggle with insufficient VRAM on our cards when using FS24, personally I have 16GB (5080) and I constantly have to balance on the limit or exceed it to get a satisfactory compromise between VRAM usage and what I see in VR - headset.
so question is .. is it a bug that enabling BAR uses so much memory or not? and is it going to be fixed in SU4 ?
You don’t have to disable Rbar in the bios. There are many games that benefit from Rbar and totally disabling it just cuz of one game that does not benefit from is a waste.
Instead, disable it per each individual game you want by using Nvidia Inspector.
Moved out from Sim Update 4 Beta | MSFS 2024 since not beta related.
unfortunately it is very related to beta buddy
but I dont play any other games, haha just using FS24 
If so, could you edit your post and add information why you think it is related to SU4 vs the Live version ?. Without such details it does not seem related at all. If you can add it then I’ll move it back to SU4.
as you wish..brds
VRAM usage as it relates to Resizable BAR has been an observation from users going back since the beginning of the year. This is not a regression of change for SU4, just something you may have noticed for the first time in the beta.
And discussed heavily within this topic as well:
Of course this is useful for those on Nvidia hardware, but many of us are not and BIOS is the only option for this setting.
Thank you for adding information but still don’t see a link with SU4. Is that a regression vs the live version ?. If you go back to the Live version and enable BAR do you observe the same behavior or not ?
See related reports:
Resizable BAR
ReBar causing VRAM overusage and decreases available VRAM amount in MSFS 2024
I too. I understand your reason.
I’m on AMD and have had to disable ReBar going back to SU2 to avoid those nasty VRAM warning messages. From time to time I’ve re-enabled it to see if the issue has been resolved but up until now it has not. As for other games, I have not noticed any discernible difference on or off so I’ll just leave it disabled for now.
Also running 3DMark tests don’t show much, if any, difference between the two.
9800X3D
RX9070XT
64 GBs 6000
I think it’s helpful to understand that Resizable Bar is doing exactly what it’s supposed to do.
Resizable Bar is a PCIe feature that allows the CPU to access the GPU’s entire video memory (VRAM) at once, instead of in small, limited chunks.
In short, the CPU can ‘dump’ data to the GPU. If it’s a lot of graphical data, VRAM can spike.
When you disable ReBAR, VRAM gets less data per processing cycle, and is able to flush it before the next ‘chunk.’
It doesn’t help that (in my opinion) the sim’s DX12 code is not properly optimized.
In reality, VRAM in FS2024 (or FS2020 when using DX12) should never fill up, as proper coding for DX12 incorporates dynamic VRAM management (as it fills up, data is discarded, based on a complex set of rules that can kind of be thought of as ‘cache management’.)
It’s not really a cache, but if you think about how a cache works to keep file size within limits (FIFO , most-used/least-used, and other methods) it’s a decent enough analogy.
This is true!
I think individual testing is key. Some people report substantial gains, some none, and some even report a detrimental effect when ReBAR is on.
A benchmark is a good start, but I think repeatable CapFrameX tests in a high resource aircraft, in a resource hungry location, is the better test.
Not a bug.
I don’t have any issues with VRAM. As for its usage in sim, MSFS 2024 is just buggy - we’re waiting for fixes.
The other thing, wouldn’t an application have to be, ‘ReBar ready’, for lack of a better term. Like any other technology I would be surprised if it works simply by turning it on. Wouldn’t the application have to make some changes to the code to take advantage of it?
I don’t know!
AFAIK, ReBar operates at the PCIe bus level. It’s either ON or OFF, controlling data transfers between the CPU and the GPU. The GPU needs to be capable of utilizing it. But as long as it’s ON and the GPU says ‘Resizable Bar’ (or something similar) ENABLED, it will work.
Some games benefit from it, and some games don’t. But that’s not a result of the game being ‘ReBAR-capable.’
That is what makes it confusing. I understand the relationship between the CPU and GPU regarding ReBar but I don’t understand why not all games would benefit from it. I figured it must have something to do with the coding. Why, in FS2024, am I getting more ‘Low VRAM’ warning messages when ReBar is enabled compared to when it’s disabled? Perhaps it’s just the DX12 coding in general, as what was mentioned earlier in this thread.
I can confirm, having tested it today, that turning off Rebar significantly reduces the number of “low VRAM” messages.