From 4d1c5acf5748b9a9b9b40cfb6ee1118593bacecd Mon Sep 17 00:00:00 2001 From: "Danilo M." Date: Thu, 29 Oct 2026 12:12:35 +0100 Subject: sound: drop the OSD's canvas grain, it broke Qt's garbage collector The desktop shell's recurring 100% CPU spin is a Qt bug set off by the volume OSD. Its grain Canvas called createImageData on every paint, and Qt 6.11 subtracts that pixel buffer from the V4 unmanaged-heap counter without having added it. The first GC after an OSD show wrapped the size_t counter, and from then on every JS allocation ran a full GC until a restart. The OSD shows on volume keys, track changes and resume, which is why the spin followed all three. Found by running each always-on unit of the desktop in its own qs with GC stats: only the sound module wrapped, 3 s after a resume, and a volume nudge reproduced it on demand. Qt's qml tool with a bare Canvas confirms it is createImageData alone: 17,856 of 17,856 GCs wrapped, the same canvas drawing with fillRect 0 of 5. With the grain removed, 8 OSD shows under forced GCs left the counter intact. The grain was alpha 14/255, so the OSD looks nearly the same. vram.sh's comment blamed the fdinfo parse for the underflow; corrected, and the lesson is in AGENTS.md. Co-Authored-By: Claude Opus 5.5 --- desktop/modules/sound/README.md | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'desktop/modules/sound/README.md') diff --git a/desktop/modules/sound/README.md b/desktop/modules/sound/README.md index c3ada08..88aba11 100644 --- a/desktop/modules/sound/README.md +++ b/desktop/modules/sound/README.md @@ -60,8 +60,9 @@ When the track has art, it also fills the whole panel as a blurred background under a dark scrim (`Theme.base` at 0.82), and the thumbnail stays sharp in the row. The palette is dark, so the scrim is what keeps text legible on a light cover; blur alone did not. The art is opaque, so it hides the -compositor's frosting while it shows, so a faint sheen and grain fake it on -the scrim. Without art the panel is unchanged. +compositor's frosting while it shows, so a faint sheen fakes it on the +scrim. It once had Canvas grain too, removed because `createImageData` +underflows Qt's GC counter (AGENTS.md). Without art the panel is unchanged. A new cover crossfades in once it has decoded, so a slow art server never fades through black. When the track has no art, or its cover fails to load, -- cgit v1.2.3