[perf-improver] perf: fast path in HumanReadableDurationFormatter.Render for sub-hour durations by Evangelink · Pull Request #8861 · microsoft/testfx

Evangelink · 2026-06-05T14:40:54Z

🤖 This is an automated contribution from Perf Improver.

Goal and Rationale

HumanReadableDurationFormatter.Render is called multiple times per terminal progress-frame render tick — once per visible test-worker line for the "duration unchanged" fast-check, and once more inside AppendTestWorkerProgress/AppendTestWorkerDetail when the line needs a full re-render. For a 4-assembly run refreshing at ~5 fps, this adds up to ~40+ calls per second over the lifetime of the test run.

Each call currently allocates:

A new StringBuilder()
One or two intermediate strings via GetFormattedPart (e.g. "5s", "59s", " 05s")
The final stringBuilder.ToString() result

That is 3–4 heap allocations per call — all for a tiny string like "(5s)" or "(2m 30s)".

Approach

On .NET 8+, use string.Create(IFormatProvider, Span<char>, ref DefaultInterpolatedStringHandler) with a stackalloc buffer. This overload uses the span as a scratch buffer and produces the final heap string in a single allocation — no StringBuilder, no intermediate GetFormattedPart strings.

The fast path activates when:

Days == 0 && Hours == 0 (covers virtually all test runs)
showMilliseconds == false (the default for all progress-frame callers)

Both conditions are true for every caller in AnsiTerminalTestProgressFrame and SimpleTerminalBase.

The slow path (days, hours, or showMilliseconds=true) is unchanged; it is rarely reached and is not in the render hot path.

Performance Evidence

Scenario	Before	After
Allocations per `Render` call (typical: < 1 min)	3–4 (StringBuilder + 1–2 GetFormattedPart strings + result)	1 (result only)
Allocations per `Render` call (> 1 hour)	3–4	3–4 (unchanged, slow path)
`string.Create` heap allocations	n/a	1 (final string only; scratch buffer is on stack)

Methodology: code inspection + allocation analysis. HumanReadableDurationFormatter.Render is called ~5× per render frame; at 5 fps over a 5-minute run that is ~7 500 calls, saving ~15 000–22 500 small string allocations.

The change is #if NET8_0_OR_GREATER-guarded, so netstandard2.0 behaviour is completely unchanged.

Trade-offs

The nested ternary (wrapInParentheses ? (minutes == 0 ? ... : ...) : (minutes == 0 ? ... : ...)) is slightly dense but self-contained. The logic is simple and the four resulting strings are easy to validate visually.
No behaviour change for showMilliseconds=true, durations with hours, or durations with days.
netstandard2.0 uses the existing slow path as before.

Test Status

Microsoft.Testing.Platform.UnitTests (net8.0): 1086 passed, 0 failed, 3 skipped ✅
Build (all TFMs: net8.0, net9.0, netstandard2.0): 0 warnings, 0 errors ✅

Reproducibility

./build.sh
artifacts/bin/Microsoft.Testing.Platform.UnitTests/Debug/net8.0/Microsoft.Testing.Platform.UnitTests

Generated by Perf Improver

Generated by Perf Improver · sonnet46 8.8M · ◷

Add this agentic workflows to your repo

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/perf-improver.md@main

… durations On .NET 8+, add a fast path that uses string.Create with a stackalloc buffer for the most common case (duration < 1 hour, no milliseconds). Before: each Render call allocated a StringBuilder + 1-2 intermediate strings from GetFormattedPart + the final result string (3-4 allocations). After (fast path): only the final result string is allocated (1 allocation). This method is called on every progress-frame render tick (roughly 5 times per frame) to format durations for each visible test-worker line. The savings accumulate quickly during long-running parallel test runs. All progress-frame callers (AnsiTerminalTestProgressFrame, SimpleTerminalBase) use the default parameters (wrapInParentheses=true, showMilliseconds=false), so they all benefit from the fast path. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

This PR optimizes HumanReadableDurationFormatter.Render in Microsoft.Testing.Platform’s terminal output path by adding a .NET 8+ fast path for the common “sub-hour, no milliseconds” case, reducing per-call allocations during frequent progress-frame rendering.

Changes:

Added a #if NET8_0_OR_GREATER fast path using string.Create with a stackalloc scratch buffer for durations where Days == 0 && Hours == 0 and showMilliseconds == false.
Kept the existing StringBuilder-based formatting as the unchanged slow path for longer durations or when milliseconds are requested.

Show a summary per file

File	Description
src/Platform/Microsoft.Testing.Platform/OutputDevice/Terminal/HumanReadableDurationFormatter.cs	Adds a .NET 8+ allocation-reducing formatting fast path for the most common progress-duration rendering scenario.

Copilot's findings

Files reviewed: 1/1 changed files
Comments generated: 0

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Copilot's findings

Files reviewed: 2/2 changed files
Comments generated: 2

Evangelink · 2026-06-07T11:20:45Z

+#if NET8_0_OR_GREATER
+        // Fast path for the common non-negative progress-frame case: duration < 1 hour with no milliseconds.
+        if (!showMilliseconds && duration.Value.Ticks >= 0 && duration.Value.Days == 0 && duration.Value.Hours == 0)
+        {
+            int seconds = duration.Value.Seconds;
+            int minutes = duration.Value.Minutes;
+
+            return (wrapInParentheses, minutes) switch
+            {
+                (true, 0) => $"({seconds}s)",
+                (true, _) => $"({minutes}m {seconds:D2}s)",
+                (false, 0) => $"{seconds}s",
+                _ => $"{minutes}m {seconds:D2}s",
+            };
+        }
+#endif


Good catch — fixed in 1b25ddc. Each fast-path arm is now wrapped with string.Create(CultureInfo.InvariantCulture, $"...") so the NET8 fast path matches the slow path's invariant numeric formatting in locales with non-ASCII digits.

Evangelink · 2026-06-07T11:20:47Z

+    [DataRow(0, true, "(0s)")]
+    [DataRow(5, true, "(5s)")]
+    [DataRow(65, true, "(1m 05s)")]
+    [DataRow(3599, true, "(59m 59s)")]
+    [DataRow(65, false, "1m 05s")]


Good catch — fixed in 1b25ddc. Added DataRows for (false, 0) with pure-second durations (0s, 5s, 59s) and the parentheses-less 59m 59s boundary so the previously-uncovered arm now has direct coverage.

…e + expand DataRows Address review feedback on PR #8861: - Wrap each fast-path interpolated string with string.Create(CultureInfo.InvariantCulture, ...) so the NET8 fast path produces the same numeric output as the slow path (which already uses InvariantCulture for numeric parts via GetFormattedPart). Without this, locales with non-ASCII digits (e.g., ar-SA, fa-IR) would see different output between the fast and slow paths. - Cover the previously-untested (wrapInParentheses: false, minutes == 0) and pure-second arms with DataRows: 0s, 5s, 59s, and the parentheses-less 59m 59s edge. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings June 5, 2026 14:40

Evangelink added area/performance Runtime / build performance / efficiency. type/automation Created or maintained by an agentic workflow. labels Jun 5, 2026

Copilot started reviewing on behalf of Evangelink June 5, 2026 14:41 View session

Copilot AI reviewed Jun 5, 2026

View reviewed changes

Evangelink marked this pull request as ready for review June 5, 2026 15:01

azat-msft approved these changes Jun 5, 2026

View reviewed changes

Youssef1313 reviewed Jun 5, 2026

View reviewed changes

Comment thread src/Platform/Microsoft.Testing.Platform/OutputDevice/Terminal/HumanReadableDurationFormatter.cs Outdated

Evangelink mentioned this pull request Jun 6, 2026

[perf-improver] Monthly Activity 2026-06 #8740

Open

2 tasks

Evangelink and others added 4 commits June 7, 2026 09:46

Simplify duration formatter fast path

1748e41

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Simplify duration formatter fast path

a239f0f

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Merge remote review updates

7c1df43

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Resolve formatter fast path style warning

8532ea5

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings June 7, 2026 08:15

Copilot started reviewing on behalf of Evangelink June 7, 2026 08:15 View session

Copilot AI reviewed Jun 7, 2026

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

[perf-improver] perf: fast path in HumanReadableDurationFormatter.Render for sub-hour durations#8861

[perf-improver] perf: fast path in HumanReadableDurationFormatter.Render for sub-hour durations#8861
Evangelink wants to merge 6 commits into
mainfrom
perf-assist/duration-formatter-fast-path-fb8645e5dcd1ce84

Evangelink commented Jun 5, 2026

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Copilot AI left a comment

Uh oh!

Evangelink Jun 7, 2026

Uh oh!

Evangelink Jun 7, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Conversation

Evangelink commented Jun 5, 2026

Goal and Rationale

Approach

Performance Evidence

Trade-offs

Test Status

Reproducibility

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Copilot's findings

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Copilot's findings

Uh oh!

Evangelink Jun 7, 2026

Choose a reason for hiding this comment

Uh oh!

Evangelink Jun 7, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants