test(benches): measure overhead on yielding

benches/Cargo.toml

@@ -56,3 +56,8 @@ harness = false
 name = "trace_id"
 path = "trace_id.rs"
 harness = false
+
+[[bench]]
+name = "yield"
+path = "yield.rs"
+harness = false

benches/yield.rs

@@ -0,0 +1,56 @@
+use std::time::{Duration, Instant};
+
+use criterion::{criterion_group, criterion_main, Criterion};
+
+use elfo::Context;
+
+mod common;
+
+fn baseline(c: &mut Criterion) {
+    async fn testee(iter_count: u64) -> Duration {
+        let start = Instant::now();
+        for _ in 0..iter_count {
+            tokio::task::yield_now().await;
+        }
+        start.elapsed()
+    }
+
+    c.bench_function("baseline", |b| {
+        b.iter_custom(|iter_count| {
+            common::make_st_runtime().block_on(async {
+                tokio::task::spawn(async move { testee(iter_count).await })
+                    .await
+                    .unwrap()
+            })
+        })
+    });
+}
+
+async fn testee(_ctx: Context, iter_count: u64) -> Duration {
+    let start = Instant::now();
+    for _ in 0..iter_count {
+        tokio::task::yield_now().await;
+    }
+    start.elapsed()
+}
+
+fn without_telemetry(c: &mut Criterion) {
+    c.bench_function("without_telemetry", |b| {
+        assert!(metrics::try_recorder().is_none());
+        b.iter_custom(|iter_count| common::bench_singleton(iter_count, testee))
+    });
+}
+
+// TODO: with stuck detection (requires runtime parameter).
+
+fn with_telemetry(c: &mut Criterion) {
+    c.bench_function("with_telemetry", |b| {
+        // Install a recorder but don't run the telemeter actor.
+        elfo::batteries::telemeter::init();
+        assert!(metrics::try_recorder().is_some());
+        b.iter_custom(|iter_count| common::bench_singleton(iter_count, testee))
+    });
+}
+
+criterion_group!(cases, baseline, without_telemetry, with_telemetry);
+criterion_main!(cases);