User has been running the more aggressive 0001 variant (skip the
watchDmaBuf wait entirely) downstream and reports Plasma feels
measurably snappier — fewer latency spikes under heavy compositor
activity. The present 0002 MR has different (correct) wait
semantics so the perceived gain can't be directly attributed, but
calling it out gives reviewers an honest signal that the patch
at least preserves whatever benefit was on the table downstream.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
KDE merge-request body for kwin-fourier patch 0002 (the
upstream-shape, not the diagnostic 0001 bypass).
Captures:
- Summary of the change (poll dmabuf fd directly, drop the
EXPORT_SYNC_FILE+sync_file roundtrip).
- Why it matters (per-frame ioctl overhead on Mali hardware,
measurable contributor to compositor latency spikes).
- Side effects (drop unused linux/dma-buf.h and xf86drm.h
includes, remove exportWaitSyncFile static helper).
- Alternative considered (16ms timeout — preserves shape but
doesn't remove the syscalls; rejected for that reason).
- Validation context on PineTab2.
- Future work pointer at the kernel-side dma_resv work.
- KDE contribution flow boilerplate: account, SSH, fork+branch
recipe, reviewer suggestions (vladz, zamundaaa, David Edmundson),
labels (Component::Wayland, Performance, Backport).
Validation gate before submitting: build kwin-fourier with 0002
instead of 0001, install on ohm, confirm equivalence with the
0001-validated playback. Strace numbers for the syscall reduction
go into the MR body once captured.
This is a parallel to the qt6 submission draft committed earlier.
test0r
marfrit