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monolith

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Commit 32fbd7e2725c

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atagen <boss@atagen.co>2026-10-16 13:32 UTC

2 files changed+115-16
monolith: keep the render budget from chasing its own misses

Taking the worst of the last 32 render times let one CPU spike push the budget past several refreshes, dropping dozens of frames after it, and slack that decayed within a third of a second at 165 Hz fell straight back into missing. The budget now uses the 90th percentile, never exceeds a refresh, and its slack decays over seconds. Slow frames log scene, render and queue time separately.
crates/monolith/src/drm.rs+36−13
@@ -82,16 +82,17 @@ impl Surface {
8282 if refresh == 0 {
8383 return None;
8484 }
85- let earliest = now + self.budget.ns();
86- let periods = earliest.saturating_sub(last).div_ceil(refresh).max(1);
85+ let budget = self.budget.ns().min(refresh);
86+ let periods = (now + budget).saturating_sub(last).div_ceil(refresh).max(1);
8787 let vblank = last + periods * refresh;
88- Some((vblank, vblank - self.budget.ns()))
88+ Some((vblank, vblank - budget))
8989 }
9090 }
9191
92-/// How long before a vblank rendering must start. The worst recent CPU
93-/// render time covers the CPU side, and a slack that grows on every missed
94-/// vblank and slowly shrinks while frames land covers GPU time and the commit.
92+/// How long before a vblank rendering must start. A high percentile of
93+/// recent CPU render times covers the CPU side without one spike inflating
94+/// it, and a slack that grows on every missed vblank and shrinks over seconds
95+/// while frames land covers GPU time and the commit.
9596 struct Budget {
9697 renders: VecDeque<u64>,
9798 slack_ns: u64,
@@ -101,7 +102,7 @@ impl Budget {
101102 const KEEP: usize = 32;
102103 const MIN_SLACK_NS: u64 = 1_000_000;
103104 const STEP_NS: u64 = 500_000;
104- const DECAY_NS: u64 = 10_000;
105+ const DECAY_NS: u64 = 1_000;
105106
106107 fn new() -> Self {
107108 Self {
@@ -111,7 +112,13 @@ impl Budget {
111112 }
112113
113114 fn ns(&self) -> u64 {
114- self.renders.iter().max().copied().unwrap_or(0) + self.slack_ns
115+ let mut renders: Vec<u64> = self.renders.iter().copied().collect();
116+ renders.sort_unstable();
117+ let p90 = renders
118+ .get(renders.len().saturating_sub(1) * 9 / 10)
119+ .copied()
120+ .unwrap_or(0);
121+ p90 + self.slack_ns
115122 }
116123
117124 fn record(&mut self, render_ns: u64) {
@@ -543,6 +550,7 @@ fn render_surface(state: &mut State, crtc: crtc::Handle, target: u64) -> bool {
543550 if local.x >= 0.0 && local.y >= 0.0 && local.x < area.w && local.y < area.h {
544551 elements.extend(cursor.elements(renderer, cursor_status, local));
545552 }
553+ let scene_began = std::time::Instant::now();
546554 elements.extend(crate::scene::build(
547555 layout,
548556 surface.id,
@@ -553,23 +561,38 @@ fn render_surface(state: &mut State, crtc: crtc::Handle, target: u64) -> bool {
553561 &config.decoration,
554562 borders,
555563 ));
564+ let scene_ns = scene_began.elapsed().as_nanos() as u64;
556565 let animating = anim.active(now);
557566 anim.prune(now);
567+ let render_began = std::time::Instant::now();
568+ let mut queue_ns = 0;
558569 match surface
559570 .drm
560571 .render_frame(renderer, &elements, CLEAR, FrameFlags::DEFAULT)
561572 {
562- Ok(result) if !result.is_empty => match surface.drm.queue_frame(()) {
563- Ok(()) => surface.queued = true,
564- Err(e) => tracing::warn!("queueing a frame failed: {e}"),
565- },
573+ Ok(result) if !result.is_empty => {
574+ let queue_began = std::time::Instant::now();
575+ match surface.drm.queue_frame(()) {
576+ Ok(()) => surface.queued = true,
577+ Err(e) => tracing::warn!("queueing a frame failed: {e}"),
578+ }
579+ queue_ns = queue_began.elapsed().as_nanos() as u64;
580+ }
566581 Ok(_) => {}
567582 Err(e) => tracing::warn!("rendering failed: {e}"),
568583 }
584+ let render_ns = render_began.elapsed().as_nanos() as u64 - queue_ns;
569585 let took = began.elapsed().as_nanos() as u64;
570586 surface.budget.record(took);
571587 if took > surface.refresh_ns / 2 {
572- tracing::debug!(output = surface.output.name(), took_ns = took, "slow frame");
588+ tracing::debug!(
589+ output = surface.output.name(),
590+ took_ns = took,
591+ scene_ns,
592+ render_ns,
593+ queue_ns,
594+ "slow frame"
595+ );
573596 }
574597 if !surface.queued {
575598 surface.target_ns = None;
monolith.log+79−3
@@ -1,5 +1,81 @@
1- Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.06s
2- Running `target/debug/monolith run --backend drm , vkcube`
1+ Finished `release` profile [optimized] target(s) in 0.07s
2+ Running `target/release/monolith run --backend drm , vkcube`
3+2026-10-16T13:18:42.960033Z INFO monolith::drm: primary GPU path=/dev/dri/card1
4+2026-10-16T13:18:43.191440Z INFO monolith::drm: output connected name="DP-2" w=2560 h=1440 refresh=165
5+2026-10-16T13:18:43.191538Z INFO monolith::ipc: control socket path=/run/user/1000/monolith-wayland-2.sock
6+2026-10-16T13:18:43.191556Z INFO monolith: monolith running socket="wayland-2" device="NVIDIA GeForce RTX 3060"
7+2026-10-16T13:18:43.192099Z INFO monolith::commands: spawned pid=339299 argv=[",", "vkcube"]
8+2026-10-16T13:18:43.206596Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=14418823
9+2026-10-16T13:18:43.212094Z DEBUG monolith::drm: frame rate output="DP-2" presented=1 vblanks=8355033 budget_us=16418
310 Selected WSI platform: wayland
411 Selected GPU 0: NVIDIA GeForce RTX 3060, type: DiscreteGpu, apiVersion: 4211017 (1.4.329), driverVersion: -1797652352 (83.416.128)
5-Io error: Broken pipe (os error 32)
12+2026-10-16T13:18:44.212377Z DEBUG monolith::drm: frame rate output="DP-2" presented=80 vblanks=165 budget_us=1784
13+2026-10-16T13:18:45.212592Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=164 budget_us=1473
14+2026-10-16T13:18:45.497520Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6009851 budget_ns=2764556
15+2026-10-16T13:18:45.830980Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6064851 budget_ns=1955919
16+2026-10-16T13:18:46.212848Z DEBUG monolith::drm: frame rate output="DP-2" presented=163 vblanks=164 budget_us=1374
17+2026-10-16T13:18:47.190680Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=3426370
18+2026-10-16T13:18:47.194947Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6049851 budget_ns=4926370
19+2026-10-16T13:18:47.213154Z DEBUG monolith::drm: frame rate output="DP-2" presented=164 vblanks=165 budget_us=4896
20+2026-10-16T13:18:48.213491Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=165 budget_us=1743
21+2026-10-16T13:18:49.140885Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=5945851 budget_ns=1965559
22+2026-10-16T13:18:49.213628Z DEBUG monolith::drm: frame rate output="DP-2" presented=164 vblanks=164 budget_us=1860
23+2026-10-16T13:18:49.225750Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6058851 budget_ns=2360210
24+2026-10-16T13:18:49.874409Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=5916851 budget_ns=3887978
25+2026-10-16T13:18:50.214055Z DEBUG monolith::drm: frame rate output="DP-2" presented=163 vblanks=165 budget_us=1653
26+2026-10-16T13:18:51.214172Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=164 budget_us=1636
27+2026-10-16T13:18:51.769798Z DEBUG monolith::input: bind cmd=Fullscreen
28+2026-10-16T13:18:51.830166Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=11023044
29+2026-10-16T13:18:51.838579Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=30315404 budget_ns=12523044
30+2026-10-16T13:18:52.214455Z DEBUG monolith::drm: frame rate output="DP-2" presented=126 vblanks=164 budget_us=12213
31+2026-10-16T13:18:53.214677Z DEBUG monolith::drm: frame rate output="DP-2" presented=164 vblanks=165 budget_us=1430
32+2026-10-16T13:18:54.215041Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=165 budget_us=1452
33+2026-10-16T13:18:55.215200Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=164 budget_us=1442
34+2026-10-16T13:18:55.403154Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6061851 budget_ns=1914018
35+2026-10-16T13:18:56.106336Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6057851 budget_ns=1942709
36+2026-10-16T13:18:56.215463Z DEBUG monolith::drm: frame rate output="DP-2" presented=163 vblanks=165 budget_us=1693
37+2026-10-16T13:18:56.332434Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=3400539
38+2026-10-16T13:18:56.336731Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6072851 budget_ns=5040539
39+2026-10-16T13:18:56.399771Z DEBUG monolith::input: bind cmd=Fullscreen
40+2026-10-16T13:18:56.462019Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=7255957
41+2026-10-16T13:18:56.470071Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=24228404 budget_ns=9255957
42+2026-10-16T13:18:56.682281Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6073851 budget_ns=2612969
43+2026-10-16T13:18:56.694386Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6049851 budget_ns=3112969
44+2026-10-16T13:18:56.809547Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6062851 budget_ns=3442969
45+2026-10-16T13:18:57.215731Z DEBUG monolith::drm: frame rate output="DP-2" presented=153 vblanks=165 budget_us=2751
46+2026-10-16T13:18:58.161784Z DEBUG monolith::input: bind cmd=Spawn { argv: ["beer"] }
47+2026-10-16T13:18:58.162414Z INFO monolith::commands: spawned pid=339323 argv=["beer"]
48+2026-10-16T13:18:58.197792Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6063851 budget_ns=3867448
49+2026-10-16T13:18:58.215976Z DEBUG monolith::drm: frame rate output="DP-2" presented=164 vblanks=165 budget_us=3837
50+2026-10-16T13:18:58.271072Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=10411692
51+2026-10-16T13:18:58.276596Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=12125255 budget_ns=12351692
52+2026-10-16T13:18:59.216233Z DEBUG monolith::drm: frame rate output="DP-2" presented=132 vblanks=165 budget_us=1525
53+2026-10-16T13:18:59.432766Z DEBUG monolith::input: bind cmd=Spawn { argv: ["beer"] }
54+2026-10-16T13:18:59.433294Z INFO monolith::commands: spawned pid=339344 argv=["beer"]
55+2026-10-16T13:18:59.458728Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6063851 budget_ns=2796776
56+2026-10-16T13:18:59.495745Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=4250817
57+2026-10-16T13:18:59.501210Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6080553 budget_ns=6220817
58+2026-10-16T13:19:00.216526Z DEBUG monolith::drm: frame rate output="DP-2" presented=142 vblanks=165 budget_us=1457
59+2026-10-16T13:19:00.835760Z DEBUG monolith::input: bind cmd=Move { dir: Left }
60+2026-10-16T13:19:00.853017Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6064851 budget_ns=3451449
61+2026-10-16T13:19:01.216794Z DEBUG monolith::drm: frame rate output="DP-2" presented=164 vblanks=164 budget_us=1462
62+2026-10-16T13:19:02.087739Z DEBUG monolith::input: bind cmd=InvertMove
63+2026-10-16T13:19:02.217007Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=164 budget_us=1381
64+2026-10-16T13:19:02.344360Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6068851 budget_ns=1788895
65+2026-10-16T13:19:02.441740Z DEBUG monolith::input: bind cmd=Move { dir: Right }
66+2026-10-16T13:19:02.497884Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=4232196
67+2026-10-16T13:19:02.501941Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6062553 budget_ns=6012196
68+2026-10-16T13:19:02.786857Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6063851 budget_ns=4654297
69+2026-10-16T13:19:03.217269Z DEBUG monolith::drm: frame rate output="DP-2" presented=159 vblanks=165 budget_us=1587
70+2026-10-16T13:19:04.217526Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=165 budget_us=1467
71+2026-10-16T13:19:04.781348Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6070851 budget_ns=3130793
72+2026-10-16T13:19:05.217834Z DEBUG monolith::drm: frame rate output="DP-2" presented=164 vblanks=165 budget_us=1442
73+2026-10-16T13:19:05.633029Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=19194939
74+2026-10-16T13:19:05.636097Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=42437851 budget_ns=20694939
75+2026-10-16T13:19:06.218058Z DEBUG monolith::drm: frame rate output="DP-2" presented=158 vblanks=164 budget_us=1463
76+2026-10-16T13:19:07.218340Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=165 budget_us=1477
77+2026-10-16T13:19:08.218585Z DEBUG monolith::drm: frame rate output="DP-2" presented=165 vblanks=164 budget_us=1636
78+2026-10-16T13:19:08.370131Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6046851 budget_ns=1989990
79+2026-10-16T13:19:09.008493Z DEBUG monolith::drm: slow frame output="DP-2" took_ns=3242045
80+2026-10-16T13:19:09.012717Z DEBUG monolith::drm: frame missed its vblank output="DP-2" late_ns=6034851 budget_ns=4742045
81+2026-10-16T13:19:09.031732Z DEBUG monolith::input: bind cmd=Quit