kms: Fix frame scheduling

src/backend/kms/drm_helpers.rs

@@ -316,6 +316,7 @@ fn get_manufacturer(vendor: &[char; 3]) -> &'static str {
     }
 }
 
+// Returns refresh rate in milliherz
 pub fn calculate_refresh_rate(mode: Mode) -> u32 {
     let htotal = mode.hsync().2 as u32;
     let vtotal = mode.vsync().2 as u32;

src/backend/kms/surface/mod.rs

@@ -594,9 +594,10 @@ impl SurfaceThreadState {
             .unwrap()
             .dmabuf_formats();
 
-        self.timings.set_refresh_interval(Some(Duration::from_nanos(
-            drm_helpers::calculate_refresh_rate(surface.pending_mode()) as u64,
-        )));
+        self.timings
+            .set_refresh_interval(Some(Duration::from_secs_f64(
+                1_000.0 / drm_helpers::calculate_refresh_rate(surface.pending_mode()) as f64,
+            )));
         self.timings.set_vrr(vrr);
 
         match DrmCompositor::new(

src/backend/kms/surface/timings.rs

@@ -3,7 +3,7 @@ use std::{collections::VecDeque, num::NonZeroU64, time::Duration};
 use smithay::utils::{Clock, Monotonic, Time};
 use tracing::error;
 
-const MIN_RENDER_TIME: Duration = Duration::from_millis(5);
+const FRAME_TIME_BUFFER: Duration = Duration::from_millis(1);
 const FRAME_TIME_WINDOW: usize = 3;
 
 pub struct Timings {
@@ -37,7 +37,7 @@ impl Frame {
     }
 
     fn frame_time(&self) -> Duration {
-        Time::elapsed(&self.render_start, self.presentation_submitted)
+        Time::elapsed(&self.render_start, self.presentation_presented)
     }
 }
 
@@ -179,18 +179,20 @@ impl Timings {
             / (self.previous_frames.len() as u32)
     }
 
-    pub fn avg_frametime(&self, window: usize) -> Duration {
-        if self.previous_frames.is_empty() || window == 0 {
-            return MIN_RENDER_TIME;
+    pub fn avg_frametime(&self, window: usize) -> Option<Duration> {
+        if self.previous_frames.len() < window || window == 0 {
+            return None;
         }
 
-        self.previous_frames
-            .iter()
-            .rev()
-            .take(window)
-            .map(|f| f.frame_time())
-            .sum::<Duration>()
-            / (window.min(self.previous_frames.len()) as u32)
+        Some(
+            self.previous_frames
+                .iter()
+                .rev()
+                .take(window)
+                .map(|f| f.frame_time())
+                .sum::<Duration>()
+                / (window.min(self.previous_frames.len()) as u32),
+        )
     }
 
     pub fn avg_fps(&self) -> f64 {
@@ -259,6 +261,10 @@ impl Timings {
             return Duration::ZERO;
         }
 
-        estimated_presentation_time.saturating_sub(self.avg_frametime(FRAME_TIME_WINDOW))
+        let Some(avg_frametime) = self.avg_frametime(FRAME_TIME_WINDOW) else {
+            return Duration::ZERO;
+        };
+
+        estimated_presentation_time.saturating_sub(avg_frametime + FRAME_TIME_BUFFER)
     }
 }

src/debug.rs

@@ -50,8 +50,8 @@ pub fn fps_ui<'a>(
 
     let amount = avg_fps.round() as usize * 2;
     let (max_disp, min_disp, avg_disp) = (
-        timings.min_frametime(amount).as_secs_f64(),
         timings.max_frametime(amount).as_secs_f64(),
+        timings.min_frametime(amount).as_secs_f64(),
         timings.avg_frametime(amount).as_secs_f64(),
     );