Using Resizable BAR (ReBAR, also known as AMD SmartAccessMemory) causes the game to experience constant microstutters. The microstutters are detected by AMD Adrenalin and displayed on the overlay, in percentile averaging up to 30~40%.
Disabling Resizable BAR in BIOS settings immediately fixes the issue and the game runs Butter smooth.
Unfortunately it is not possible to record the AMD Adrenalin overlay without an external capture card. I can only record the overlay from the screen with my phone for example. Blame AMD.
Possibly affected systems: All AM4 and AM5 systems running latest AGESA.
Original bugreport regarding this issue:
https://community.gaijin.net/issues/p/warthunder/i/SXjg3M4fK4TF
(I will translate it bellow)
I will try to do as the Bug Report Manager suggested and record the additional information.
In the mean time, if you are having constant stutters, try disabling Resizable BAR and see if it fixes it for you.
I know everyone wants it on because it improves performance and FPS in most games.
But having more people try this can help to see on what kind of systems the issue is present.
My system is as follows:
MSI AM4 motherboard,
2x16 32GB DDR4 System memory running in dual channel mode
Ryzen 5600X CPU
AMD Radeon RX 9070XT GPU
Original text from the bugreport, into English:
Severe Stuttering and FPS Drops on Modern PCs with Resizable BAR Enabled (Dagor Engine)
Problem Description
On modern computers with Resizable BAR (ReBAR) enabled, games running on Dagor Engine exhibit noticeable stuttering, frame-time spikes, and short FPS drops despite having a high average FPS.
It is important to note that on most modern systems Resizable BAR is enabled by default, since in the vast majority of contemporary games it improves performance and reduces CPU load. As a result, this issue affects a significant portion of users with current-generation hardware.
Technical Cause (Where the Engine Breaks)
Dagor Engine uses a memory management model designed around small aperture-based VRAM mappings and frequent CPU-side operations on GPU resources.
When Resizable BAR is enabled, the CPU gains access to large contiguous regions of VRAM. However, the engine:
- Performs synchronous CPU accesses to GPU-visible memory
- Relies on implicit synchronization barriers and forced flush operations
- Does not account for the fact that working with large ReBAR mappings requires asynchronous streaming and explicit synchronization management
As a result, during resource processing or streaming, the engine regularly triggers:
- CPU↔GPU stalls
- Blocking waits for command completion
- Command buffer flushes
Why the Issue Manifests as Stuttering
Frames render quickly until the engine accesses a large region of ReBAR-mapped memory. At that moment, forced synchronization occurs, delaying the frame and causing a micro-freeze. The cycle then repeats.
Why Disabling ReBAR Helps
With Resizable BAR disabled:
- VRAM access occurs through smaller memory windows
- The driver takes over more asynchronous memory management
- The engine’s incorrect assumptions about memory access patterns are effectively masked
Expected Behavior
Stable frame times and smooth performance on modern systems with Resizable BAR enabled.
Actual Behavior
Regular stuttering, frame-time spikes, and short FPS drops.
Temporary Workaround
Disabling Resizable BAR in the BIOS or GPU driver, which, however, reduces performance in most other games.
Conclusion
The issue is related to an outdated resource streaming and CPU–GPU synchronization model that does not work correctly with the large contiguous VRAM regions provided by Resizable BAR, which is enabled by default on modern systems.