Prune commentary and stale Rust port notes

scripts/rigs/ui-profile/tests/arena_churn.rs

@@ -1,51 +1,17 @@
-//! What each GPU arena costs to upload per frame, at layer 1 (docs/RUST.md's
-//! "Three test layers") -- the real transcript screen over the real bench
-//! fixture, with no window, no compositor and no GPU.
-//!
-//!     cargo test --release --test arena_churn -- --ignored --nocapture
-//!
-//! from `scripts/rigs/ui-profile/`.
-//!
-//! It exists because the upload is the one part of a frame that layer 1
-//! *builds* and never performs, so `frame_profile.rs` cannot see it at
-//! all: the emulator's `stream: build p50` stayed at 10.5ms across a
-//! change that nearly halved layer 1's CPU frame, and nothing could say
-//! why until this could count bytes.
-//!
-//! Three numbers per array per frame, which is the point of the rig --
-//! any two of them alone are misleading:
-//!
-//! - **changed** is the floor: entries whose bytes actually differ from
-//!   the previous frame, found by diffing. Nothing correct can upload
-//!   less.
-//! - **uploaded** is what `iris` really writes, read from the same
-//!   `Dirty` sets `UiRenderNode::update` consumes and cleared here the
-//!   way an upload would clear them. Above `changed` by whatever the
-//!   marking over-marks plus whatever range coalescing pulls in.
-//! - **whole** is what the old code wrote every time anything changed.
-//!
-//! `#[ignore]`d and assertion-free: it prints distributions, so
-//! `run-tests.sh` neither runs it nor can fail on it.
-
 use ai_app::ui::fixture::{PHONE_FRAME_MS, PHONE_SCALE, phone_size};
 use iris::harness::Harness;
 use iris::prelude::{GlyphPrimitive, Primitive, RectPrimitive};
 use iris::widget::Scrollable;
 use ui_profile::stats::pct_u64;
 
-/// Passes over the same content, alternating direction -- the same
-/// out-and-back `frame_profile.rs`'s fling drives, so the two rigs
-/// describe the same gesture.
 const PASSES: usize = 8;
 const VELOCITY: f32 = 12_000.0;
 const PASS_CAP_MS: u64 = 4_000;
 
-/// One array's per-frame totals.
 #[derive(Default)]
 struct Tally {
     name: &'static str,
     stride: usize,
-    /// The previous frame's bytes, for the diff that finds the floor.
     prev: Vec<u8>,
     changed: Vec<u64>,
     uploaded: Vec<u64>,
@@ -62,7 +28,6 @@ impl Tally {
         }
     }
 
-    /// Records one frame, and clears the dirty set as an upload would.
     fn frame(&mut self, bytes: &[u8], ranges: Vec<std::ops::Range<usize>>) {
         let n = self.prev.len().min(bytes.len()) / self.stride;
         let mut changed = (0..n)
@@ -71,8 +36,6 @@ impl Tally {
                 self.prev[r.clone()] != bytes[r]
             })
             .count();
-        // Everything past the old end is new, and so is dirty by
-        // definition.
         changed += bytes.len() / self.stride - n;
         self.changed.push((changed * self.stride) as u64);
         self.uploaded
@@ -85,11 +48,8 @@ impl Tally {
 
     fn report(&mut self) {
         let sum = |v: &[u64]| v.iter().sum::<u64>();
-        let (changed, uploaded, whole) = (
-            sum(&self.changed),
-            sum(&self.uploaded),
-            sum(&self.whole),
-        );
+        let (changed, uploaded, whole) =
+            (sum(&self.changed), sum(&self.uploaded), sum(&self.whole));
         println!(
             "  {:<10} whole {:>7.1} MB | uploaded {:>7.1} MB ({:>5.1}%) | floor {:>7.1} MB ({:>5.1}%)",
             self.name,
@@ -114,9 +74,6 @@ impl Tally {
     }
 }
 
-/// The three arenas a transcript frame writes. Masks and move offsets are
-/// left out deliberately: they are a hundred-odd entries, so their whole
-/// buffer is smaller than one range of any of these.
 struct Arenas {
     instances: Tally,
     rects: Tally,
@@ -132,15 +89,11 @@ impl Arenas {
         }
     }
 
-    /// Reads this frame's dirty ranges out of the render state and clears
-    /// them, exactly as `UiRenderNode::update` would on a real backend.
     fn frame(&mut self, h: &mut Harness) {
         let count = h.render.primitives.instances().len();
         let (entries, dirty) = h.render.primitives.instances_for_upload();
-        // `PrimitiveInstance` is not exported, so the stride comes from
-        // the slice rather than from `size_of`.
         let bytes: Vec<u8> = bytemuck::cast_slice(entries).to_vec();
-        self.instances.stride = if count == 0 { 48 } else { bytes.len() / count };
+        self.instances.stride = bytes.len().checked_div(count).unwrap_or(48);
         let ranges = dirty.ranges(count, 1024 / self.instances.stride);
         dirty.clear();
         self.instances.frame(&bytes, ranges);
@@ -196,7 +149,6 @@ fn what_a_fling_uploads() {
                 break;
             }
         }
-        // A moment at rest between passes, as a finger would leave.
         t += 200;
     }
     println!("\na fling, {PASSES} passes:");