https://bugs.kde.org/show_bug.cgi?id=515751
Bug ID: 515751
Summary: Severe Bluetooth HID input jitter regression affecting
game controllers in KDE Plasma 6.5.4 and newer.
Classification: KDE Neon
Product: neon
Version First unspecified
Reported In:
Platform: Neon
OS: Linux
Status: REPORTED
Severity: grave
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected]
Target Milestone: ---
SUMMARY
Severe Bluetooth HID input jitter regression affecting game controllers in KDE
Plasma 6.5.4 and newer.
The issue makes gaming unplayable, especially for competitive or precision
gameplay, and affects real users across multiple Bluetooth adapters and
controllers.
High polling rate controllers over Bluetooth exhibit significantly worse
jitter, while lower polling rate controllers are less affected.
This behavior did not occur in Plasma 6.5.3, where Bluetooth controller input
was stable and usable.
The problem is present on Wayland and X11, persists across updates (6.5.4 →
6.5.5), and is not related to GPU drivers, power management, or graphics stack.
USB connection does not show jitter, confirming the issue is specific to
Bluetooth input handling.
STEPS TO REPRODUCE
Boot into KDE Plasma 6.5.4 or newer (Wayland or X11).
Connect a game controller via Bluetooth.
Open a game, gamepad tester, or any application requiring precise analog or
button input.
Move analog sticks or perform rapid button inputs.
OBSERVED RESULT
Noticeable input jitter, stutter, and inconsistent timing on
Bluetooth-connected controllers.
The issue is more severe on high polling rate controllers.
Gameplay feels unstable and unreliable.
Competitive gaming and precision input are effectively unplayable.
The problem occurs:
On Wayland and X11
With NVIDIA and safe graphics mode
With multiple Bluetooth adapters
USB connection works correctly with no jitter.
EXPECTED RESULT
Bluetooth controller input should be stable, smooth, and consistent, matching
behavior seen in Plasma 6.5.3.
High polling rate controllers should not suffer excessive jitter.
Bluetooth and USB input latency/jitter should be comparable, as they were
before the regression.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE neon (Ubuntu 24.04 base)
KDE Plasma Version: 6.5.4 / 6.5.5
KDE Frameworks Version: 6.22.x
Qt Version: 6.10.1
Kernel: 6.x (issue reproduced across kernels)
BLUETOOTH ADAPTERS TESTED
Intel Dual Band Wireless-AC 7260
→ High jitter (severe)
Realtek RTL8771B Bluetooth Radio
→ Jitter present
TP-Link Bluetooth 5.3 UB5A
→ Jitter reduced but still present
→ Low/normal polling rate controllers mostly usable
→ High polling rate controllers still show high jitter
CONTROLLERS TESTED
Sony DualShock 4 (original)
DualShock 4 Data Frog P03
Wolf V-6 controller
All affected over Bluetooth.
All work correctly over USB.
ADDITIONAL INFORMATION
This is a regression: the issue was not present in Plasma 6.5.3.
Occurs regardless of compositor (Wayland/X11).
Not resolved by:
Power management tweaks
CPU governor changes
Disabling C-states
NVIDIA driver updates
Safe graphics mode
USB input path is unaffected, confirming Bluetooth-specific behavior.
The issue impacts real users, especially those playing competitive or
latency-sensitive games.
TECHNICAL HYPOTHESIS (Bluetooth / HID Timing)
Based on testing across multiple controllers, adapters, and Plasma versions,
the issue appears to be related to Bluetooth HID event timing and scheduling,
rather than controller firmware, hardware, or graphics stack.
Key observations:
The jitter only occurs when controllers are connected via Bluetooth.
The same controllers exhibit no jitter over USB.
The issue is worse on high polling rate controllers, suggesting:
Input events may be batched, delayed, or unevenly scheduled
Event timestamps may be handled inconsistently
The problem affects multiple Bluetooth adapters and vendors, making
adapter-specific firmware issues unlikely.
The regression coincides with Plasma 6.5.4, and was not present in 6.5.3.
Possible areas involved:
BlueZ HID input event timing or buffering
Bluetooth HID interrupt/event scheduling
KDE / KWin / libinput input processing changes affecting Bluetooth devices
Event coalescing, throttling, or resampling introduced in Plasma 6.5.4
Higher-frequency HID reports being mishandled compared to lower polling rate
devices
Additional hints:
Low or normal polling rate controllers are less affected, while high polling
rate controllers exhibit severe jitter.
This suggests that higher report frequency may exceed or trigger a timing edge
case in the Bluetooth → input stack.
Both Wayland and X11 are affected, pointing away from compositor-specific
rendering issues and toward shared input infrastructure.
While this report does not identify the exact faulty component, the behavior
strongly suggests a regression in Bluetooth HID input timing introduced after
Plasma 6.5.3.
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