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/Osd.qml | 33 ++++----------------------------- 1 file changed, 4 insertions(+), 29 deletions(-) (limited to 'desktop/modules/sound/Osd.qml') diff --git a/desktop/modules/sound/Osd.qml b/desktop/modules/sound/Osd.qml index f60f5ce..e66d559 100644 --- a/desktop/modules/sound/Osd.qml +++ b/desktop/modules/sound/Osd.qml @@ -186,9 +186,10 @@ Scope { color: Qt.alpha(Theme.base, 0.82) } - // Frost on the scrim, faked: a faint top-down sheen and fixed - // grain. The art is opaque, so the compositor's frosting - // cannot show here without costing the scrim its legibility. + // Frost on the scrim, faked: a faint top-down sheen. The art is + // opaque, so the compositor's frosting cannot show here + // without costing the scrim its legibility. No grain: see + // createImageData in AGENTS.md. Rectangle { anchors.fill: parent radius: bgMask.radius @@ -197,32 +198,6 @@ Scope { GradientStop { position: 0.6; color: "transparent" } } } - - // ponytail: grain painted once with Canvas; a ShaderEffect - // would animate or scale better but needs a compiled .qsb. - Canvas { - anchors.fill: parent - layer.enabled: true - layer.effect: MultiEffect { - maskEnabled: true - maskSource: bgMask - maskThresholdMin: 0.5 - maskSpreadAtMin: 1.0 - } - onPaint: { - if (width <= 0 || height <= 0) return; - const ctx = getContext("2d"); - const img = ctx.createImageData(width, height); - for (let i = 0; i < img.data.length; i += 4) { - const v = Math.random() * 255; - img.data[i] = v; - img.data[i + 1] = v; - img.data[i + 2] = v; - img.data[i + 3] = 14; - } - ctx.putImageData(img, 0, 0); - } - } } HoverHandler { -- cgit v1.2.3