7 files changed, 48 insertions, 5 deletions
diff --git a/cli/js/40_testing.js b/cli/js/40_testing.js
index 21417db23..afa9a6552 100644
--- a/cli/js/40_testing.js
+++ b/cli/js/40_testing.js
@@ -849,7 +849,7 @@ function compareMeasurements(a, b) {
   return 0;
 }
 
-function benchStats(n, highPrecision, avg, min, max, all) {
+function benchStats(n, highPrecision, usedExplicitTimers, avg, min, max, all) {
   return {
     n,
     min,
@@ -859,6 +859,8 @@ function benchStats(n, highPrecision, avg, min, max, all) {
     p995: all[MathCeil(n * (99.5 / 100)) - 1],
     p999: all[MathCeil(n * (99.9 / 100)) - 1],
     avg: !highPrecision ? (avg / n) : MathCeil(avg / n),
+    highPrecision,
+    usedExplicitTimers,
   };
 }
 
@@ -926,7 +928,7 @@ async function benchMeasure(timeBudget, fn, async, context) {
   wavg /= c;
 
   // measure step
-  if (wavg > lowPrecisionThresholdInNs || usedExplicitTimers) {
+  if (wavg > lowPrecisionThresholdInNs) {
     let iterations = 10;
     let budget = timeBudget * 1e6;
 
@@ -978,6 +980,8 @@ async function benchMeasure(timeBudget, fn, async, context) {
       }
     }
   } else {
+    context.start = function start() {};
+    context.end = function end() {};
     let iterations = 10;
     let budget = timeBudget * 1e6;
 
@@ -986,8 +990,6 @@ async function benchMeasure(timeBudget, fn, async, context) {
         const t1 = benchNow();
         for (let c = 0; c < lowPrecisionThresholdInNs; c++) {
           fn(context);
-          currentBenchUserExplicitStart = null;
-          currentBenchUserExplicitEnd = null;
         }
         const iterationTime = (benchNow() - t1) / lowPrecisionThresholdInNs;
 
@@ -1019,7 +1021,15 @@ async function benchMeasure(timeBudget, fn, async, context) {
   }
 
   all.sort(compareMeasurements);
-  return benchStats(n, wavg > lowPrecisionThresholdInNs, avg, min, max, all);
+  return benchStats(
+    n,
+    wavg > lowPrecisionThresholdInNs,
+    usedExplicitTimers,
+    avg,
+    min,
+    max,
+    all,
+  );
 }
 
 /** @param desc {BenchDescription} */
diff --git a/cli/tests/integration/bench_tests.rs b/cli/tests/integration/bench_tests.rs
index 73d541aa6..214dfaa50 100644
--- a/cli/tests/integration/bench_tests.rs
+++ b/cli/tests/integration/bench_tests.rs
@@ -187,6 +187,11 @@ itest!(bench_explicit_start_end {
   exit_code: 1,
 });
 
+itest!(bench_explicit_start_end_low_precision {
+  args: "bench --quiet -A bench/explicit_start_and_end_low_precision.ts",
+  output: "bench/explicit_start_and_end_low_precision.out",
+});
+
 itest!(bench_with_config {
   args: "bench --config bench/collect/deno.jsonc bench/collect",
   exit_code: 0,
diff --git a/cli/tests/testdata/bench/explicit_start_and_end_low_precision.out b/cli/tests/testdata/bench/explicit_start_and_end_low_precision.out
new file mode 100644
index 000000000..e9ac5a864
--- /dev/null
+++ b/cli/tests/testdata/bench/explicit_start_and_end_low_precision.out
@@ -0,0 +1,9 @@
+cpu: [WILDCARD]
+runtime: deno [WILDCARD] ([WILDCARD])
+
+[WILDCARD]/explicit_start_and_end_low_precision.ts
+benchmark                    time (avg)        iter/s             (min … max)       p75       p99      p995
+----------------------------------------------------------------------------- -----------------------------
+noop with start and end  [WILDCARD] [WILDCARD]/iter[WILDCARD]([WILDCARD] … [WILDCARD]) [WILDCARD]
+Warning: start() and end() calls in "noop with start and end" are ignored because it averages less
+than 0.01s per iteration. Remove them for better results.
diff --git a/cli/tests/testdata/bench/explicit_start_and_end_low_precision.ts b/cli/tests/testdata/bench/explicit_start_and_end_low_precision.ts
new file mode 100644
index 000000000..23bdf19fe
--- /dev/null
+++ b/cli/tests/testdata/bench/explicit_start_and_end_low_precision.ts
@@ -0,0 +1,4 @@
+Deno.bench("noop with start and end", (b) => {
+  b.start();
+  b.end();
+});
diff --git a/cli/tools/bench/mod.rs b/cli/tools/bench/mod.rs
index 247422f71..d876c2504 100644
--- a/cli/tools/bench/mod.rs
+++ b/cli/tools/bench/mod.rs
@@ -106,6 +106,7 @@ pub struct BenchDescription {
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
 pub struct BenchStats {
   pub n: u64,
   pub min: f64,
@@ -115,6 +116,8 @@ pub struct BenchStats {
   pub p99: f64,
   pub p995: f64,
   pub p999: f64,
+  pub high_precision: bool,
+  pub used_explicit_timers: bool,
 }
 
 impl BenchReport {
diff --git a/cli/tools/bench/reporters.rs b/cli/tools/bench/reporters.rs
index 6b1e885a9..68788bc96 100644
--- a/cli/tools/bench/reporters.rs
+++ b/cli/tools/bench/reporters.rs
@@ -236,6 +236,10 @@ impl BenchReporter for ConsoleReporter {
           )
         );
 
+        if !stats.high_precision && stats.used_explicit_timers {
+          println!("{}", colors::yellow(format!("Warning: start() and end() calls in \"{}\" are ignored because it averages less\nthan 0.01s per iteration. Remove them for better results.", &desc.name)));
+        }
+
         self.group_measurements.push((desc, stats.clone()));
       }
 
diff --git a/cli/tsc/dts/lib.deno.ns.d.ts b/cli/tsc/dts/lib.deno.ns.d.ts
index 436387eba..610ed1061 100644
--- a/cli/tsc/dts/lib.deno.ns.d.ts
+++ b/cli/tsc/dts/lib.deno.ns.d.ts
@@ -1011,6 +1011,10 @@ declare namespace Deno {
     /** Restarts the timer for the bench measurement. This should be called
      * after doing setup work which should not be measured.
      *
+     * Warning: This method should not be used for benchmarks averaging less
+     * than 0.01s per iteration. In such cases it will be disabled but the call
+     * will still have noticeable overhead, resulting in a warning.
+     *
      * ```ts
      * Deno.bench("foo", async (t) => {
      *   const data = await Deno.readFile("data.txt");
@@ -1024,6 +1028,10 @@ declare namespace Deno {
     /** End the timer early for the bench measurement. This should be called
      * before doing teardown work which should not be measured.
      *
+     * Warning: This method should not be used for benchmarks averaging less
+     * than 0.01s per iteration. In such cases it will be disabled but the call
+     * will still have noticeable overhead, resulting in a warning.
+     *
      * ```ts
      * Deno.bench("foo", async (t) => {
      *   const file = await Deno.open("data.txt");