LSP perf optimizations by andrewbranch · Pull Request #64877 · microsoft/TypeScript

Andrew Branch (andrewbranch) · 2026-10-19T19:12:56Z

I let Copilot spin for a while on LSP performance, profiling the vscode repo. Several of these changes affect batch compilation too.

Baseline (vscode)

Bench	time/op	B/op	allocs/op
InitialLoad	1.2–2.5 s	3.04 GB (2595 MB retained)	–
EditOpenFile	13–22 ms	14 MB	–
EditImports	115–146 ms	277 MB	3.26 M
WatchChange	6–8 ms	–	–
CreateDeleteFile	335–375 ms	291 MB	3.46 M
TsconfigChange	~339 ms	–	–

Heap of initial load: ~95% of retained memory is ASTs/symbols in the parse cache (core compiler).
Project-package retained structures are small; the project package's leverage is mostly transient
allocation and per-change latency.

Cumulative result (merge-base `3789ddb` vs HEAD, vscode, interleaved runs, n=6)

Bench	time	B/op	allocs/op	retained
InitialLoad	~ (1.29 → 1.15 s, noisy)	−3.7%	−15.6%	−2 MB (of 2.4 GB)
EditOpenFile (fast clone)	~	−4.9%	−23.3%	−24% (14.0 → 10.7 MB)
WatchChange (fast clone from disk)	~ (3–4 ms, noisy)	−16.0%	−90.4%	–
EditImports (program rebuild)	~/−19%*	−37.6%	−41.8%	−17%
CreateDeleteFile (file-name reload + rebuild)	−43%	−38.6%	−41.2%	−12%
TsconfigChange (ParsedCommandLine + rebuild)	−40%	−38.9%	−41.4%	−12%
AutoImportInitial	~	−3.1%	−0.5%	−15.6% (19.8 → 16.7 MB)
AutoImportEdit	~	−4.8%	−44.1%	–

* EditImports: 165 → 97 ms in a direct A/B of the final fix; ~ in the noisy cumulative run.
Timings were taken with load average 10–20 from other processes; B/op and allocs/op are exact.

Experiments

1. `dirty.SyncMap.LoadClean` fast path in snapshotFSBuilder — COMMITTED (`0a35842`; benchmarks in dd354e654af)

dirty.SyncMap.Load allocates a SyncMapEntry wrapper on every hit in the immutable base map.
snapshotFSBuilder's GetFileByPath/FileExists/GetAccessibleEntries only need read access, so
added LoadClean returning the base value without allocation when the key is not dirty.

EditImports allocs −4.7%; CreateDeleteFile allocs −4.6%, time −4.6%; B/op −1.9%.

2. parseTask hot/cold split (compiler/filesparser.go) — COMMITTED (`cea07f4`)

Program rebuild profile showed parseTask allocations prominent. Removed two dead fields and moved
load-result fields to a lazily allocated *parseTaskResult (only tasks that actually load need
them; failed-lookup/duplicate tasks don't). parseTask 368 B → 184 B.

EditImports / CreateDeleteFile B/op −7.4%, allocs +0.3%. Timing within noise.

3. Concurrent directory prefetch in vfsmatch — COMMITTED (`39911ff`)

CPU profile of CreateDeleteFile/TsconfigChange: ~80% of updateProgram CPU is
ReloadFileNamesOfParsedCommandLine → vfsmatch.matchFileNames → sequential os.ReadDir
over the whole include tree (snapshot cachedvfs is fresh per snapshot, so it hits disk every time).
Added a prefetch phase that reads the same directories concurrently, then the original
serial walk runs unchanged using the prefetched entries (falling back to the host for anything
missing). Results/ordering/symlink-cycle semantics are unchanged.

CreateDeleteFile 374 → 218 ms, TsconfigChange 354 → 178 ms (p=0.002, wide variance).
B/op +1%, allocs +0.5% (prefetch bookkeeping).
Also benefits initial load and tsc CLI config parsing.

4. sourceFS seen-file tracking + overlayFS no-clone — COMMITTED (`039e5dd`)

sourceFS.FileExists computed a PathKey for tracking and again for the lookup, and stored into
seenFiles unconditionally. Compute the key once, Load before Store; overlayFS stopped cloning
its overlay map on read paths.

Rebuild benches allocs −2–3%, B/op −2%.

5. packagejson.InfoCache cheap Clone — COMMITTED (`14e9882`; RWMutex variant squashed away)

ReuseProgram (every edit / watch change) clones the package.json info cache; cloning a
sync.Map entry-by-entry allocated per entry (~6.6k allocs per WatchChange).

First version (RWMutex + plain map): WatchChange −30% time, −90% allocs; EditOpenFile −14% time.
But EditImports regressed +38% time (119 → 165 ms): RWMutex reader-count contention during
parallel module resolution. Found only via a cumulative merge-base A/B + bisect — lesson: every
concurrency-touching change needs a rebuild-heavy timing check.
Final version: immutable base map read lock-free + collections.SyncMap overlay for new entries;
Clone = maps.Clone(base) + overlay merge. Keeps clone wins; EditImports 165 → 97 ms
(faster than the original 119 ms), −2% allocs. -race clean.

6. autoimport `Export` 248 → 192 B — COMMITTED (`b975755`)

Registry retained memory is dominated by Export (~52k exports on vscode). ModuleID stores one
string + kind instead of two strings; ExportSyntax, lsutil.ScriptElementKind narrowed to uint8;
fields reordered to remove padding.

AutoImportInitial retained −15.7% (19.8 → 16.7 MB). Time/allocs unchanged.

7. tsoptions extension-priority sibling keys — COMMITTED (`c09c9b0`)

getFileNamesFromConfigSpecs built ChangeExtension + canonical key for each higher/lower-priority
sibling of every wildcard file and appended a flattened group slice per file (~57% of file-name
expansion allocs). Now derives sibling keys from one canonical key (stemKey + ext, falling back to
the old path for unknown extensions / dynamic names), iterating groups in place.
Verified with a temporary 20k-case randomized differential test against the old implementation.

TsconfigChange / CreateDeleteFile B/op −2.1%, allocs −1.8%.

8. Module resolution: resolve candidate once — COMMITTED (`de88374`)

resolutionCandidateFromEncodedPaths resolved the same relative specifier twice (ResolveFile and
ResolveDirectory) whenever the file and directory inputs were identical (always, outside dynamic
files); both produce identical strings. Resolve once.

TsconfigChange B/op −12.8%, allocs −13.2%, time −10%; InitialLoad allocs −5%, time −11%.

9. tspath leading `./` / `../` fast path — COMMITTED (`9496c1e`)

ResolveFile/ResolveDirectory for ./x, ../../x concatenated then normalized (2 allocs). Now
walks the directory up for leading dot segments and concatenates once; falls back for any other dot
segments or ascending past root. 200k-case randomized differential test (disk, drive, URL, UNC,
dynamic roots) against the old path.

TsconfigChange B/op −12.1%, allocs −12.9%, time −8%; InitialLoad allocs −4.8%, time −9%.

10. parseTask references resolution PackageId — COMMITTED (`02e334f`)

parseTask/resolvedRef carried a 64 B inline PackageId (empty for nearly all files). Now a
pointer into the already-heap-allocated resolution (nil when empty). parseTask 184 → 136 B
(192 → 144 size class), no new allocations.

TsconfigChange B/op −3.8%.

11. Co-allocated referenced-file include reasons — COMMITTED (`570e356`)

Each import allocated FileIncludeReason (56 B) + referencedFileData (32 B) separately; both are
retained by the program. fileIncludeKind → uint8 (48 B) and one constructor co-allocates both
(80 B, 1 alloc). Net −13 lines.

TsconfigChange allocs −4.8%, B/op −1%; InitialLoad retained −2 MB.

12. `parallelWorkGroup.Queue` wrapper closure — COMMITTED (`d248609`)

Queue wrapped fn in func(){ fn() } before wg.Go. Pass fn directly.

TsconfigChange allocs −5.6%, InitialLoad allocs −2%. One-line change, benefits all parallel work.

dirty.SyncMap.Load allocates an entry wrapper on every hit in the base map. snapshotFSBuilder reads only need the value, so add LoadClean, which returns base values without allocating when the key is not dirty. Perf (vscode, unpinned; indicative): EditImports -4.7% allocs; CreateDeleteFile -4.6% allocs, -1.9% B/op. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

parseTask is allocated for every file reference edge, but most edges point at files that are already loaded. Moving load results into a side record and removing two unused fields shrinks parseTask from 368B to 184B. Perf (vscode, unpinned; indicative): EditImports and CreateDeleteFile -7.4% B/op, +0.3% allocs; time within noise. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

Andrew Branch (andrewbranch) · 2026-10-19T19:13:35Z

TypeScript Bot (@typescript-bot) perf test this

typescript-automation · 2026-10-19T19:13:42Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`perf test this`	✅ Started	👀 Results

typescript-automation · 2026-10-19T19:46:37Z

Andrew Branch (@andrewbranch)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - native}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_115,276	_115,276	_~	_~	_~	_{p=1.000 n=12}
_Types	_79,613	_79,613	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{113,591k (± 0.05%)}	_{113,606k (± 0.06%)}	_~	_113,452k	_113,759k	_{p=0.660 n=12}
_{Memory Allocs}	_{2,212,531 (± 0.01%)}	_{2,212,213 (± 0.01%)}	_{-318 (- 0.01%)}	_2,211,984	_2,212,601	_{p=0.001 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.049s (± 3.78%)}	_{0.049s (± 2.36%)}	_~	_0.045s	_0.051s	_{p=0.920 n=12}
_{Bind Time}	_{0.018s (± 8.26%)}	_{0.017s (± 8.52%)}	_~	_0.014s	_0.022s	_{p=0.135 n=12}
_{Check Time}	_{0.562s (± 1.04%)}	_{0.559s (± 0.99%)}	_~	_0.550s	_0.579s	_{p=0.096 n=12}
_{Emit Time}	_{0.328s (± 2.17%)}	_{0.322s (± 2.24%)}	_~	_0.309s	_0.342s	_{p=0.213 n=12}
_{Total Time}	_{0.965s (± 0.80%)}	_{0.955s (± 0.74%)}	_~	_0.937s	_0.973s	_{p=0.057 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{846,983 (± 0.06%)}	_{846,942 (± 0.04%)}	_~	_846,110	_848,011	_{p=0.977 n=12}
_Types	_{247,031 (± 0.00%)}	_{247,031 (± 0.00%)}	_~	_247,030	_247,033	_{p=0.982 n=12}
_{Memory Used}	_{596,501k (± 0.04%)}	_{596,189k (± 0.03%)}	_{-313k (- 0.05%)}	_595,847k	_596,751k	_{p=0.028 n=12}
_{Memory Allocs}	_{13,141,800 (± 0.04%)}	_{13,078,059 (± 0.07%)}	_{-63,742 (- 0.49%)}	_13,066,562	_13,111,453	_{p=0.000 n=12}
_{Config Time}	_0.020s	_0.015s	_{🟩-0.005s (-25.00%)}	_~	_~	_{p=0.000 n=12}
_{Parse Time}	_{0.282s (± 1.83%)}	_{0.290s (± 2.15%)}	_{+0.008s (+ 2.75%)}	_0.272s	_0.310s	_{p=0.046 n=12}
_{Bind Time}	_{0.102s (±10.03%)}	_{0.081s (± 6.83%)}	_{🟩-0.021s (-20.79%)}	_0.071s	_0.097s	_{p=0.002 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.860s (± 1.54%)}	_{1.879s (± 1.65%)}	_~	_1.784s	_1.923s	_{p=0.164 n=12}
_{Total Time}	_{2.288s (± 1.34%)}	_{2.282s (± 1.47%)}	_~	_2.183s	_2.343s	_{p=0.843 n=12}
_{mui-docs - native}
_Errors	_11,405	_11,405	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_4,331,983	_4,331,983	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,370,520	_1,370,520	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{2,625,492k (± 0.06%)}	_{2,624,302k (± 0.07%)}	_~	_2,620,262k	_2,628,363k	_{p=0.443 n=12}
_{Memory Allocs}	_{27,694,010 (± 0.07%)}	_{27,439,831 (± 0.07%)}	_{-254,179 (- 0.92%)}	_27,385,334	_27,502,889	_{p=0.000 n=12}
_{Config Time}	_{0.020s (± 0.90%)}	_0.015s	_{🟩-0.005s (-25.31%)}	_~	_~	_{p=0.000 n=12}
_{Parse Time}	_{0.580s (± 3.00%)}	_{0.558s (± 3.05%)}	_~	_0.511s	_0.593s	_{p=0.060 n=12}
_{Bind Time}	_{0.003s (±24.75%)}	_{0.003s (±24.75%)}	_~	_0.002s	_0.006s	_{p=1.000 n=12}
_{Check Time}	_{8.658s (± 0.28%)}	_{8.565s (± 0.34%)}	_{-0.093s (- 1.07%)}	_8.518s	_8.689s	_{p=0.000 n=12}
_{Emit Time}	_{0.706s (±10.82%)}	_{0.595s (±13.32%)}	_{🟩-0.111s (-15.69%)}	_0.498s	_0.801s	_{p=0.027 n=12}
_{Total Time}	_{10.901s (± 0.52%)}	_{10.620s (± 1.03%)}	_{-0.281s (- 2.58%)}	_10.416s	_10.856s	_{p=0.000 n=12}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,388,680	_1,388,680	_~	_~	_~	_{p=1.000 n=12}
_Types	_441,862	_441,862	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{1,312,862k (± 0.64%)}	_{1,316,123k (± 0.70%)}	_~	_1,296,678k	_1,336,647k	_{p=0.443 n=12}
_{Memory Allocs}	_{78,130,520 (± 0.14%)}	_{77,907,481 (± 0.09%)}	_{-223,039 (- 0.29%)}	_77,603,392	_78,084,042	_{p=0.004 n=12}
_{Config Time}	_{0.005s (±11.96%)}	_{0.007s (± 9.00%)}	_{🔻+0.002s (+44.64%)}	_0.005s	_0.008s	_{p=0.000 n=12}
_{Parse Time}	_{0.311s (± 2.04%)}	_{0.302s (± 2.21%)}	_~	_0.286s	_0.320s	_{p=0.081 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{2.005s (± 0.48%)}	_{2.010s (± 0.42%)}	_~	_1.991s	_2.036s	_{p=0.325 n=12}
_{Emit Time}	_{0.359s (± 4.50%)}	_{0.345s (± 4.33%)}	_~	_0.302s	_0.389s	_{p=0.311 n=12}
_{Total Time}	_{23.910s (± 0.68%)}	_{23.690s (± 0.66%)}	_{-0.220s (- 0.92%)}	_23.156s	_23.976s	_{p=0.045 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_334,953	_334,953	_~	_~	_~	_{p=1.000 n=12}
_Types	_197,616	_197,616	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{247,540k (± 0.03%)}	_{247,488k (± 0.03%)}	_~	_247,245k	_247,669k	_{p=0.111 n=12}
_{Memory Allocs}	_{4,329,822 (± 0.01%)}	_{4,326,464 (± 0.01%)}	_{-3,358 (- 0.08%)}	_4,325,511	_4,327,582	_{p=0.000 n=12}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.112s (± 4.75%)}	_{0.116s (± 4.45%)}	_~	_0.100s	_0.124s	_{p=0.172 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{0.954s (± 0.45%)}	_{0.957s (± 0.56%)}	_~	_0.945s	_0.973s	_{p=0.503 n=12}
_{Emit Time}	_{0.156s (± 3.77%)}	_{0.148s (± 5.88%)}	_~	_0.129s	_0.173s	_{p=0.164 n=12}
_{Total Time}	_{1.278s (± 0.58%)}	_{1.277s (± 0.93%)}	_~	_1.246s	_1.304s	_{p=0.943 n=12}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_303,834	_303,834	_~	_~	_~	_{p=1.000 n=12}
_Types	_181,663	_181,663	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{215,260k (± 0.02%)}	_{215,234k (± 0.01%)}	_~	_215,162k	_215,324k	_{p=0.291 n=12}
_{Memory Allocs}	_{1,401,676 (± 0.02%)}	_{1,401,236 (± 0.01%)}	_{-439 (- 0.03%)}	_1,400,774	_1,401,743	_{p=0.006 n=12}
_{Config Time}	_0.000s	_{0.000s (±217.90%)}	_~	_0.000s	_0.001s	_{p=1.000 n=12}
_{Parse Time}	_{0.097s (± 3.53%)}	_{0.096s (± 5.19%)}	_~	_0.088s	_0.111s	_{p=0.450 n=12}
_{Bind Time}	_{0.040s (±11.70%)}	_{0.040s (± 9.88%)}	_~	_0.030s	_0.048s	_{p=0.701 n=12}
_{Check Time}	_{0.745s (± 0.94%)}	_{0.743s (± 1.02%)}	_~	_0.726s	_0.762s	_{p=0.681 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.897s (± 0.76%)}	_{0.895s (± 0.96%)}	_~	_0.877s	_0.926s	_{p=0.766 n=12}
_{vscode - native}
_Errors	₃₉₆	₃₉₆	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_12,483,880	_12,483,880	_~	_~	_~	_{p=1.000 n=12}
_Types	_4,085,331	_4,085,331	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{5,845,353k (± 0.03%)}	_{5,843,014k (± 0.01%)}	_{-2,339k (- 0.04%)}	_5,840,755k	_5,844,615k	_{p=0.006 n=12}
_{Memory Allocs}	_{59,433,051 (± 0.02%)}	_{58,315,740 (± 0.01%)}	_{-1,117,310 (- 1.88%)}	_58,306,315	_58,334,956	_{p=0.000 n=12}
_{Config Time}	_{0.076s (± 0.41%)}	_{0.049s (± 0.66%)}	_{🟩-0.027s (-35.15%)}	_0.049s	_0.050s	_{p=0.000 n=12}
_{Parse Time}	_{1.816s (± 1.93%)}	_{1.825s (± 2.42%)}	_~	_1.691s	_1.944s	_{p=0.799 n=12}
_{Bind Time}	_{0.717s (±14.97%)}	_{0.594s (±14.70%)}	_{🟩-0.123s (-17.19%)}	_0.503s	_0.954s	_{p=0.024 n=12}
_{Check Time}	_{15.749s (± 1.09%)}	_{15.911s (± 0.98%)}	_~	_15.443s	_16.158s	_{p=0.236 n=12}
_{Emit Time}	_{5.809s (± 6.98%)}	_{5.454s (± 4.56%)}	_~	_4.875s	_6.361s	_{p=0.128 n=12}
_{Total Time}	_{24.259s (± 1.25%)}	_{23.917s (± 0.67%)}	_{-0.342s (- 1.41%)}	_23.585s	_24.600s	_{p=0.039 n=12}
_{webpack - native}
_Errors	₅₉₈	₅₉₈	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,343,495	_1,343,495	_~	_~	_~	_{p=1.000 n=12}
_Types	_651,492	_651,492	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{855,319k (± 0.01%)}	_{855,121k (± 0.02%)}	_{-198k (- 0.02%)}	_854,687k	_855,444k	_{p=0.039 n=12}
_{Memory Allocs}	_{6,770,093 (± 0.01%)}	_{6,724,154 (± 0.02%)}	_{-45,939 (- 0.68%)}	_6,720,654	_6,730,113	_{p=0.000 n=12}
_{Config Time}	_{0.008s (± 4.38%)}	_{0.006s (± 2.98%)}	_{🟩-0.001s (-18.89%)}	_0.006s	_0.007s	_{p=0.000 n=12}
_{Parse Time}	_{0.239s (± 3.29%)}	_{0.236s (± 4.35%)}	_~	_0.212s	_0.270s	_{p=0.541 n=12}
_{Bind Time}	_{0.062s (±12.73%)}	_{0.077s (±18.28%)}	_~	_0.054s	_0.109s	_{p=0.070 n=12}
_{Check Time}	_{2.324s (± 0.50%)}	_{2.269s (± 0.70%)}	_{-0.054s (- 2.35%)}	_2.228s	_2.299s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{2.664s (± 0.33%)}	_{2.619s (± 0.44%)}	_{-0.045s (- 1.68%)}	_2.583s	_2.639s	_{p=0.000 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,060,810	_1,060,810	_~	_~	_~	_{p=1.000 n=12}
_Types	_389,671	_389,671	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{471,799k (± 0.02%)}	_{471,755k (± 0.03%)}	_~	_471,531k	_472,243k	_{p=0.377 n=12}
_{Memory Allocs}	_{4,216,884 (± 0.11%)}	_{4,191,660 (± 0.16%)}	_{-25,224 (- 0.60%)}	_4,175,456	_4,218,103	_{p=0.000 n=12}
_{Config Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.109s (± 2.96%)}	_{0.107s (± 2.74%)}	_~	_0.103s	_0.118s	_{p=0.464 n=12}
_{Bind Time}	_{0.035s (±17.20%)}	_{0.035s (±18.46%)}	_~	_0.026s	_0.056s	_{p=0.719 n=12}
_{Check Time}	_{0.907s (± 1.25%)}	_{0.906s (± 1.01%)}	_~	_0.887s	_0.933s	_{p=0.876 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.059s (± 1.17%)}	_{1.057s (± 0.89%)}	_~	_1.026s	_1.081s	_{p=0.899 n=12}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
mui-docs - native
strada-build-src - native
strada-compiler - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

lsp

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-UnionsLSP - native}
_{Req 1 - updateOpen}	_{11ms (±20.59%)}	_{12ms (±12.45%)}	_~	_9ms	_15ms	_{p=0.056 n=12}
_{Req 2 - geterr}	_{541ms (± 0.36%)}	_{535ms (± 0.28%)}	_{-6ms (- 1.06%)}	_532ms	_539ms	_{p=0.000 n=12}
_{Req 3 - references}	_{44ms (± 4.33%)}	_{47ms (± 4.01%)}	_{🔻+2ms (+ 5.08%)}	_43ms	_51ms	_{p=0.028 n=12}
_{Req 4 - navto}	_{16ms (± 1.90%)}	_{17ms (± 5.69%)}	_~	_16ms	_21ms	_{p=0.369 n=12}
_{Req 5 - completionInfo count}	_1,363	_1,363	_~	_~	_~	_{p=1.000 n=12}
_{Req 5 - completionInfo}	_{16ms (± 7.93%)}	_{16ms (± 8.87%)}	_~	_14ms	_21ms	_{p=0.304 n=12}
_{CompilerLSP - native}
_{Req 1 - updateOpen}	_{13ms (±13.31%)}	_{11ms (±13.99%)}	_~	_10ms	_17ms	_{p=0.440 n=12}
_{Req 2 - geterr}	_{284ms (± 0.67%)}	_{285ms (± 0.48%)}	_~	_281ms	_288ms	_{p=0.940 n=12}
_{Req 3 - references}	_{49ms (± 1.17%)}	_{49ms (± 1.44%)}	_~	_48ms	_51ms	_{p=0.760 n=12}
_{Req 4 - navto}	_{19ms (± 8.20%)}	_{18ms (± 6.17%)}	_~	_17ms	_22ms	_{p=0.139 n=12}
_{Req 5 - completionInfo count}	_1,525	_1,525	_~	_~	_~	_{p=1.000 n=12}
_{Req 5 - completionInfo}	_{20ms (±11.45%)}	_{20ms (±11.60%)}	_~	_15ms	_24ms	_{p=0.725 n=12}

System info unknown

Hosts

native

Scenarios

CompilerLSP - native
Compiler-UnionsLSP - native
xstate-main-1-LSP - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

startup

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{lsp-startup - native}
_{Execution time}	_{4.66ms (±365.09%)}	_{4.67ms (±365.09%)}	_{+0.01ms (+ 0.25%)}	_0.00ms	_472.63ms	_{p=0.000 n=1200}
_{tsgo-startup - native}
_{Execution time}	_{5.67ms (±365.09%)}	_{5.68ms (±365.09%)}	_{+0.01ms (+ 0.20%)}	_0.00ms	_572.39ms	_{p=0.000 n=1200}

System info unknown

Hosts

native

Scenarios

lsp-startup - native
tsgo-startup - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

Developer Information:

Download Benchmarks

Config file-name expansion read the include tree with sequential ReadDir calls. Up to GOMAXPROCS readers now read the same directories first (honoring excludes and depth), then the unchanged ordered walk runs over the prefetched entries, so results and ordering are identical. The caller is the first reader and more workers start only while queued directories outnumber idle ones, so leaf scans start no goroutines. Directories under overlapping base paths are read once. Symlinked directories are left to the ordered walk, which owns realpath deduplication; each directory spelling is read at most once by the prefetch. A host panic stops the workers and is re-raised on the caller. With --singleThreaded, config expansion reads directories serially. Perf (vscode@9c4bcec0bb91, machine under load, interleaved A/B): CreateDeleteFile 374 -> 218 ms, TsconfigChange 354 -> 178 ms (p=0.002, n=6, wide variance); +1% B/op, +0.5% allocs. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

…files Also return host directory entries directly from overlayFS when no overlay directory affects them. Perf (vscode, unpinned; indicative): program-rebuild benchmarks -2-3% allocs, -2% B/op. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

ReuseProgram clones the package.json info cache on every edit; copying a sync.Map entry-by-entry allocated per entry. Reads now hit an immutable base map without locking, new entries go to a sync.Map overlay (first writer wins), and Clone flattens both into a new base. Perf (vscode, unpinned; indicative): WatchChange -90% allocs; EditImports and EditOpenFile time not regressed (an RWMutex variant regressed EditImports +38% from read-lock contention). Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

Store ModuleID's path/specifier in a single string (only one is ever set), narrow ExportSyntax and ScriptElementKind to uint8, and reorder small fields to avoid padding. Perf (vscode, unpinned; indicative): AutoImportInitial retained memory -15.7% (19.8 -> 16.7 MB); time and allocs unchanged. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

Perf (vscode, unpinned; indicative): TsconfigChange and CreateDeleteFile -2.1% B/op, -1.8% allocs. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

Perf (vscode, unpinned; indicative): TsconfigChange -12.8% B/op, -13.2% allocs; InitialLoad -5% allocs. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

…tring Perf (vscode, unpinned; indicative): TsconfigChange -12.1% B/op, -12.9% allocs; InitialLoad -4.8% allocs. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

…tes) Perf (vscode, unpinned; indicative): TsconfigChange -3.8% B/op; allocs unchanged. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

… 80B/1) Perf (vscode, unpinned; indicative): TsconfigChange -4.8% allocs, -1% B/op; InitialLoad retained memory -2 MB. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

Perf (vscode, unpinned; indicative): TsconfigChange -5.6% allocs; InitialLoad -2% allocs. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

Copilot

🔵 Needs a closer look

Concurrent filesystem traversal and compiler-wide representation changes warrant human review, particularly without executed validation.

No open issues 🎉

1 resolved since last review

Single-threaded mode still performs concurrent directory reads

_{Review effort: Balanced}

Andrew Branch (andrewbranch) · 2026-10-19T21:21:10Z

TypeScript Bot (@typescript-bot) perf test

typescript-automation · 2026-10-19T21:21:16Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`perf test`	✅ Started	👀 Results

typescript-automation · 2026-10-19T21:52:41Z

Andrew Branch (@andrewbranch)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - native}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_115,276	_115,276	_~	_~	_~	_{p=1.000 n=12}
_Types	_79,613	_79,613	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{113,527k (± 0.07%)}	_{113,538k (± 0.07%)}	_~	_113,376k	_113,791k	_{p=0.887 n=12}
_{Memory Allocs}	_{2,212,615 (± 0.01%)}	_{2,212,232 (± 0.01%)}	_{-383 (- 0.02%)}	_2,211,899	_2,212,916	_{p=0.001 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.049s (± 3.28%)}	_{0.048s (± 3.43%)}	_~	_0.045s	_0.055s	_{p=0.659 n=12}
_{Bind Time}	_{0.017s (±10.21%)}	_{0.017s (± 8.41%)}	_~	_0.013s	_0.020s	_{p=0.639 n=12}
_{Check Time}	_{0.561s (± 0.56%)}	_{0.558s (± 0.71%)}	_~	_0.550s	_0.568s	_{p=0.172 n=12}
_{Emit Time}	_{0.328s (± 2.74%)}	_{0.324s (± 1.98%)}	_~	_0.303s	_0.338s	_{p=0.680 n=12}
_{Total Time}	_{0.963s (± 1.03%)}	_{0.955s (± 0.95%)}	_~	_0.931s	_0.977s	_{p=0.486 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{846,989 (± 0.06%)}	_{846,907 (± 0.08%)}	_~	_845,756	_848,830	_{p=0.630 n=12}
_Types	_{247,031 (± 0.00%)}	_{247,032 (± 0.00%)}	_~	_247,030	_247,044	_{p=0.536 n=12}
_{Memory Used}	_{596,350k (± 0.02%)}	_{596,208k (± 0.03%)}	_~	_595,800k	_596,572k	_{p=0.178 n=12}
_{Memory Allocs}	_{13,138,240 (± 0.01%)}	_{13,074,668 (± 0.05%)}	_{-63,571 (- 0.48%)}	_13,065,745	_13,095,793	_{p=0.000 n=12}
_{Config Time}	_{0.020s (± 1.21%)}	_{0.015s (± 1.20%)}	_{🟩-0.005s (-25.21%)}	_0.015s	_0.016s	_{p=0.000 n=12}
_{Parse Time}	_{0.279s (± 1.87%)}	_{0.287s (± 2.65%)}	_~	_0.274s	_0.314s	_{p=0.109 n=12}
_{Bind Time}	_{0.102s (±15.67%)}	_{0.077s (± 4.75%)}	_{🟩-0.024s (-23.96%)}	_0.068s	_0.089s	_{p=0.008 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.878s (± 1.59%)}	_{1.874s (± 1.69%)}	_~	_1.803s	_1.950s	_{p=0.855 n=12}
_{Total Time}	_{2.298s (± 1.18%)}	_{2.269s (± 1.40%)}	_~	_2.202s	_2.352s	_{p=0.291 n=12}
_{arktype - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,757,463	_1,757,463	_~	_~	_~	_{p=1.000 n=12}
_Types	_943,966	_943,966	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{703,690k (± 0.01%)}	_{703,618k (± 0.01%)}	_~	_703,517k	_703,856k	_{p=0.091 n=12}
_{Memory Allocs}	_{13,293,129 (± 0.02%)}	_{13,275,828 (± 0.01%)}	_{-17,301 (- 0.13%)}	_13,273,723	_13,278,395	_{p=0.000 n=12}
_{Config Time}	_0.003s	_{0.002s (±12.64%)}	_{🟩-0.001s (-25.00%)}	_0.002s	_0.003s	_{p=0.000 n=12}
_{Parse Time}	_{0.091s (± 3.94%)}	_{0.086s (± 3.19%)}	_{🟩-0.005s (- 5.65%)}	_0.080s	_0.095s	_{p=0.023 n=12}
_{Bind Time}	_{0.027s (±13.06%)}	_{0.027s (±10.60%)}	_~	_0.024s	_0.036s	_{p=1.000 n=12}
_{Check Time}	_{2.450s (± 0.30%)}	_{2.439s (± 0.39%)}	_~	_2.411s	_2.463s	_{p=0.071 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{2.623s (± 0.41%)}	_{2.607s (± 0.36%)}	_{-0.016s (- 0.63%)}	_2.577s	_2.630s	_{p=0.045 n=12}
_{mui-docs - native}
_Errors	_11,405	_11,405	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_4,331,983	_4,331,983	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,370,520	_1,370,520	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{2,625,122k (± 0.05%)}	_{2,624,401k (± 0.07%)}	_~	_2,620,409k	_2,628,701k	_{p=0.551 n=12}
_{Memory Allocs}	_{27,702,105 (± 0.06%)}	_{27,433,011 (± 0.05%)}	_{-269,094 (- 0.97%)}	_27,401,450	_27,465,329	_{p=0.000 n=12}
_{Config Time}	_{0.020s (± 1.52%)}	_{0.015s (± 1.61%)}	_{🟩-0.005s (-25.41%)}	_0.015s	_0.016s	_{p=0.000 n=12}
_{Parse Time}	_{0.590s (± 3.07%)}	_{0.550s (± 3.42%)}	_{🟩-0.040s (- 6.82%)}	_0.511s	_0.597s	_{p=0.005 n=12}
_{Bind Time}	_{0.002s (±13.40%)}	_{0.003s (±12.54%)}	_~	_0.002s	_0.003s	_{p=0.684 n=12}
_{Check Time}	_{8.637s (± 0.13%)}	_{8.526s (± 0.56%)}	_{-0.110s (- 1.28%)}	_8.384s	_8.717s	_{p=0.000 n=12}
_{Emit Time}	_{0.725s (±10.10%)}	_{0.661s (±13.47%)}	_~	_0.499s	_0.800s	_{p=1.000 n=12}
_{Total Time}	_{10.886s (± 0.74%)}	_{10.652s (± 0.98%)}	_{-0.235s (- 2.15%)}	_10.432s	_10.825s	_{p=0.000 n=12}
_{sentry - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_7,459,653	_7,459,653	_~	_~	_~	_{p=1.000 n=12}
_Types	_2,647,172	_2,647,172	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{3,803,448k (± 0.03%)}	_{3,801,312k (± 0.03%)}	_{-2,136k (- 0.06%)}	_3,799,112k	_3,804,847k	_{p=0.006 n=12}
_{Memory Allocs}	_{77,165,486 (± 0.08%)}	_{76,682,925 (± 0.06%)}	_{-482,561 (- 0.63%)}	_76,569,505	_76,806,352	_{p=0.000 n=12}
_{Config Time}	_{0.060s (± 0.51%)}	_{0.041s (± 0.69%)}	_{🟩-0.019s (-31.63%)}	_0.041s	_0.042s	_{p=0.000 n=12}
_{Parse Time}	_{1.033s (± 3.80%)}	_{0.994s (± 2.01%)}	_~	_0.931s	_1.034s	_{p=0.091 n=12}
_{Bind Time}	_{0.308s (±12.10%)}	_{0.286s (±11.98%)}	_~	_0.255s	_0.418s	_{p=0.171 n=12}
_{Check Time}	_{14.777s (± 0.51%)}	_{14.582s (± 0.19%)}	_{-0.196s (- 1.32%)}	_14.509s	_14.635s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{16.251s (± 0.45%)}	_{15.970s (± 0.17%)}	_{-0.281s (- 1.73%)}	_15.883s	_16.024s	_{p=0.000 n=12}
_{social-app - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_2,568,629	_2,568,629	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,163,035	_1,163,035	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{1,212,943k (± 0.01%)}	_{1,212,506k (± 0.01%)}	_{-437k (- 0.04%)}	_1,211,908k	_1,212,922k	_{p=0.000 n=12}
_{Memory Allocs}	_{13,987,652 (± 0.17%)}	_{13,885,118 (± 0.42%)}	_{-102,534 (- 0.73%)}	_13,819,844	_14,156,480	_{p=0.000 n=12}
_{Config Time}	_{0.017s (± 1.65%)}	_{0.013s (± 2.45%)}	_{🟩-0.005s (-26.57%)}	_0.012s	_0.013s	_{p=0.000 n=12}
_{Parse Time}	_{0.357s (± 1.24%)}	_{0.341s (± 2.23%)}	_{🟩-0.015s (- 4.28%)}	_0.328s	_0.371s	_{p=0.001 n=12}
_{Bind Time}	_{0.079s (±10.12%)}	_{0.086s (±15.80%)}	_~	_0.068s	_0.129s	_{p=0.382 n=12}
_{Check Time}	_{3.647s (± 0.26%)}	_{3.615s (± 0.33%)}	_{-0.033s (- 0.90%)}	_3.578s	_3.639s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{4.122s (± 0.40%)}	_{4.078s (± 0.46%)}	_{-0.044s (- 1.07%)}	_4.030s	_4.127s	_{p=0.001 n=12}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,388,680	_1,388,680	_~	_~	_~	_{p=1.000 n=12}
_Types	_441,862	_441,862	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{1,312,483k (± 0.57%)}	_{1,315,779k (± 0.35%)}	_~	_1,305,802k	_1,331,129k	_{p=0.319 n=12}
_{Memory Allocs}	_{78,202,041 (± 0.13%)}	_{77,890,688 (± 0.11%)}	_{-311,353 (- 0.40%)}	_77,574,236	_78,104,482	_{p=0.000 n=12}
_{Config Time}	_{0.005s (± 8.27%)}	_{0.005s (±13.27%)}	_~	_0.004s	_0.007s	_{p=0.152 n=12}
_{Parse Time}	_{0.308s (± 1.73%)}	_{0.303s (± 2.34%)}	_~	_0.287s	_0.321s	_{p=0.311 n=12}
_{Bind Time}	_{0.000s (±217.90%)}	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{2.012s (± 0.62%)}	_{2.000s (± 0.41%)}	_~	_1.981s	_2.020s	_{p=0.091 n=12}
_{Emit Time}	_{0.348s (± 4.09%)}	_{0.341s (± 4.09%)}	_~	_0.314s	_0.387s	_{p=0.418 n=12}
_{Total Time}	_{23.880s (± 0.50%)}	_{23.596s (± 0.69%)}	_{-0.284s (- 1.19%)}	_23.230s	_23.973s	_{p=0.010 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_334,953	_334,953	_~	_~	_~	_{p=1.000 n=12}
_Types	_197,616	_197,616	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{247,490k (± 0.03%)}	_{247,433k (± 0.02%)}	_~	_247,298k	_247,526k	_{p=0.068 n=12}
_{Memory Allocs}	_{4,329,511 (± 0.01%)}	_{4,325,973 (± 0.01%)}	_{-3,538 (- 0.08%)}	_4,324,662	_4,326,755	_{p=0.000 n=12}
_{Config Time}	_{0.001s (±37.93%)}	_{0.000s (±77.74%)}	_~	_0.000s	_0.001s	_{p=0.214 n=12}
_{Parse Time}	_{0.090s (± 4.63%)}	_{0.095s (± 4.22%)}	_~	_0.084s	_0.107s	_{p=0.057 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{0.798s (± 0.76%)}	_{0.793s (± 0.70%)}	_~	_0.784s	_0.815s	_{p=0.202 n=12}
_{Emit Time}	_{0.124s (± 4.53%)}	_{0.128s (± 3.42%)}	_~	_0.116s	_0.139s	_{p=0.323 n=12}
_{Total Time}	_{1.056s (± 0.51%)}	_{1.063s (± 0.64%)}	_~	_1.039s	_1.080s	_{p=0.070 n=12}
_{t3code-server - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_11,588,087	_11,588,087	_~	_~	_~	_{p=1.000 n=12}
_Types	_3,062,556	_3,062,556	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{3,946,543k (± 0.01%)}	_{3,944,580k (± 0.01%)}	_{-1,964k (- 0.05%)}	_3,943,226k	_3,946,342k	_{p=0.000 n=12}
_{Memory Allocs}	_{41,547,231 (± 0.06%)}	_{41,381,098 (± 0.04%)}	_{-166,133 (- 0.40%)}	_41,345,948	_41,423,159	_{p=0.000 n=12}
_{Config Time}	_0.006s	_{0.005s (± 3.57%)}	_{🟩-0.001s (-15.28%)}	_0.005s	_0.006s	_{p=0.000 n=12}
_{Parse Time}	_{0.570s (± 2.52%)}	_{0.549s (± 1.99%)}	_~	_0.529s	_0.597s	_{p=0.071 n=12}
_{Bind Time}	_{0.181s (±16.62%)}	_{0.196s (±10.08%)}	_~	_0.153s	_0.244s	_{p=0.074 n=12}
_{Check Time}	_{18.663s (± 0.39%)}	_{18.592s (± 0.46%)}	_{-0.071s (- 0.38%)}	_18.447s	_18.923s	_{p=0.045 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{19.435s (± 0.38%)}	_{19.364s (± 0.43%)}	_~	_19.241s	_19.713s	_{p=0.066 n=12}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_303,834	_303,834	_~	_~	_~	_{p=1.000 n=12}
_Types	_181,663	_181,663	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{215,235k (± 0.02%)}	_{215,252k (± 0.01%)}	_~	_215,171k	_215,313k	_{p=0.504 n=12}
_{Memory Allocs}	_{1,401,665 (± 0.02%)}	_{1,401,192 (± 0.02%)}	_{-472 (- 0.03%)}	_1,400,416	_1,401,892	_{p=0.014 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.079s (± 3.93%)}	_{0.079s (± 5.04%)}	_~	_0.069s	_0.088s	_{p=0.921 n=12}
_{Bind Time}	_{0.033s (±10.26%)}	_{0.033s (± 8.87%)}	_~	_0.024s	_0.040s	_{p=0.921 n=12}
_{Check Time}	_{0.618s (± 1.19%)}	_{0.613s (± 0.99%)}	_~	_0.603s	_0.631s	_{p=0.433 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.743s (± 0.93%)}	_{0.738s (± 0.83%)}	_~	_0.719s	_0.751s	_{p=0.504 n=12}
_{vscode - native}
_Errors	₃₉₆	₃₉₆	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_12,489,159	_12,489,159	_~	_~	_~	_{p=1.000 n=12}
_Types	_4,083,411	_4,083,411	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{5,851,727k (± 0.03%)}	_{5,849,628k (± 0.01%)}	_{-2,099k (- 0.04%)}	_5,846,813k	_5,851,034k	_{p=0.020 n=12}
_{Memory Allocs}	_{59,515,692 (± 0.04%)}	_{58,399,500 (± 0.01%)}	_{-1,116,191 (- 1.88%)}	_58,386,594	_58,418,313	_{p=0.000 n=12}
_{Config Time}	_{0.062s (± 0.50%)}	_{0.040s (± 1.81%)}	_{🟩-0.022s (-35.03%)}	_0.040s	_0.044s	_{p=0.000 n=12}
_{Parse Time}	_{1.448s (± 2.72%)}	_{1.456s (± 2.21%)}	_~	_1.384s	_1.528s	_{p=0.630 n=12}
_{Bind Time}	_{0.631s (±11.98%)}	_{0.479s (± 9.59%)}	_{🟩-0.152s (-24.04%)}	_0.409s	_0.625s	_{p=0.003 n=12}
_{Check Time}	_{13.637s (± 1.13%)}	_{13.652s (± 1.10%)}	_~	_13.352s	_13.947s	_{p=0.590 n=12}
_{Emit Time}	_{4.662s (± 5.30%)}	_{4.824s (± 6.76%)}	_~	_4.207s	_5.533s	_{p=0.551 n=12}
_{Total Time}	_{20.522s (± 0.81%)}	_{20.526s (± 0.97%)}	_~	_20.167s	_21.028s	_{p=0.755 n=12}
_{webpack - native}
_Errors	₅₉₈	₅₉₈	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,343,495	_1,343,495	_~	_~	_~	_{p=1.000 n=12}
_Types	_651,492	_651,492	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{855,379k (± 0.01%)}	_{855,138k (± 0.02%)}	_{-241k (- 0.03%)}	_854,686k	_855,431k	_{p=0.006 n=12}
_{Memory Allocs}	_{6,768,818 (± 0.01%)}	_{6,730,140 (± 0.16%)}	_{-38,678 (- 0.57%)}	_6,720,048	_6,772,058	_{p=0.000 n=12}
_{Config Time}	_0.009s	_0.008s	_{🟩-0.001s (-11.11%)}	_~	_~	_{p=0.000 n=12}
_{Parse Time}	_{0.319s (± 2.46%)}	_{0.298s (± 3.43%)}	_{🟩-0.021s (- 6.54%)}	_0.267s	_0.329s	_{p=0.004 n=12}
_{Bind Time}	_{0.075s (± 8.20%)}	_{0.094s (±17.94%)}	_~	_0.069s	_0.141s	_{p=0.065 n=12}
_{Check Time}	_{2.773s (± 0.48%)}	_{2.714s (± 0.79%)}	_{-0.059s (- 2.14%)}	_2.670s	_2.767s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{3.212s (± 0.43%)}	_{3.150s (± 0.47%)}	_{-0.063s (- 1.95%)}	_3.110s	_3.191s	_{p=0.000 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,060,810	_1,060,810	_~	_~	_~	_{p=1.000 n=12}
_Types	_389,671	_389,671	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{471,862k (± 0.02%)}	_{471,798k (± 0.04%)}	_~	_471,451k	_472,393k	_{p=0.266 n=12}
_{Memory Allocs}	_{4,223,145 (± 0.08%)}	_{4,188,389 (± 0.11%)}	_{-34,756 (- 0.82%)}	_4,174,846	_4,204,036	_{p=0.000 n=12}
_{Config Time}	_0.003s	_0.002s	_{🟩-0.001s (-33.33%)}	_~	_~	_{p=0.000 n=12}
_{Parse Time}	_{0.134s (± 3.69%)}	_{0.135s (± 3.15%)}	_~	_0.125s	_0.149s	_{p=0.504 n=12}
_{Bind Time}	_{0.051s (±13.15%)}	_{0.048s (±14.59%)}	_~	_0.035s	_0.069s	_{p=0.522 n=12}
_{Check Time}	_{1.089s (± 0.76%)}	_{1.087s (± 1.01%)}	_~	_1.065s	_1.123s	_{p=0.258 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.285s (± 0.69%)}	_{1.279s (± 0.89%)}	_~	_1.248s	_1.305s	_{p=0.451 n=12}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
arktype - native
mui-docs - native
sentry - native
social-app - native
strada-build-src - native
strada-compiler - native
t3code-server - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

lsp

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-UnionsLSP - native}
_{Req 1 - updateOpen}	_{10ms (±13.94%)}	_{12ms (±15.38%)}	_~	_9ms	_17ms	_{p=0.218 n=12}
_{Req 2 - geterr}	_{540ms (± 0.33%)}	_{535ms (± 0.36%)}	_{-6ms (- 1.09%)}	_529ms	_539ms	_{p=0.000 n=12}
_{Req 3 - references}	_{45ms (± 4.26%)}	_{47ms (± 5.29%)}	_~	_39ms	_50ms	_{p=0.202 n=12}
_{Req 4 - navto}	_{16ms (± 1.90%)}	_{17ms (± 1.99%)}	_~	_16ms	_17ms	_{p=0.680 n=12}
_{Req 5 - completionInfo count}	_1,363	_1,363	_~	_~	_~	_{p=1.000 n=12}
_{Req 5 - completionInfo}	_{15ms (± 5.26%)}	_{16ms (± 6.17%)}	_~	_14ms	_19ms	_{p=0.522 n=12}
_{CompilerLSP - native}
_{Req 1 - updateOpen}	_{12ms (±16.30%)}	_{10ms (± 1.80%)}	_~	_10ms	_11ms	_{p=0.223 n=12}
_{Req 2 - geterr}	_{283ms (± 0.32%)}	_{284ms (± 0.66%)}	_~	_280ms	_288ms	_{p=0.280 n=12}
_{Req 3 - references}	_{48ms (± 2.25%)}	_{48ms (± 1.35%)}	_~	_45ms	_49ms	_{p=0.417 n=12}
_{Req 4 - navto}	_{17ms (± 1.43%)}	_{18ms (± 6.75%)}	_~	_17ms	_22ms	_{p=0.112 n=12}
_{Req 5 - completionInfo count}	_1,525	_1,525	_~	_~	_~	_{p=1.000 n=12}
_{Req 5 - completionInfo}	_{22ms (± 5.76%)}	_{20ms (±11.11%)}	_~	_15ms	_23ms	_{p=0.106 n=12}

System info unknown

Hosts

native

Scenarios

CompilerLSP - native
Compiler-UnionsLSP - native
xstate-main-1-LSP - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

startup

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{lsp-startup - native}
_{Execution time}	_{4.64ms (±365.09%)}	_{4.66ms (±365.08%)}	_{+0.02ms (+ 0.38%)}	_0.00ms	_468.21ms	_{p=0.000 n=1200}
_{tsgo-startup - native}
_{Execution time}	_{5.69ms (±365.09%)}	_{5.72ms (±365.10%)}	_{+0.03ms (+ 0.50%)}	_0.00ms	_580.57ms	_{p=0.020 n=1200}

System info unknown

Hosts

native

Scenarios

lsp-startup - native
tsgo-startup - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

Developer Information:

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Andrew Branch (andrewbranch) and others added 2 commits October 16, 2026 16:21

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Andrew Branch (andrewbranch) force-pushed the lsp-perf branch from d248609 to 8384f49 Compare October 19, 2026 20:56

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Andrew Branch (andrewbranch) and others added 10 commits October 19, 2026 14:06

core: pass queued work directly to WaitGroup.Go

06d2d96

Perf (vscode, unpinned; indicative): TsconfigChange -5.6% allocs; InitialLoad -2% allocs. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: afcfca01-a049-4749-ad08-1c00c586f6a1

Andrew Branch (andrewbranch) force-pushed the lsp-perf branch from 8384f49 to 06d2d96 Compare October 19, 2026 21:09

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LSP perf optimizations - #64877

LSP perf optimizations#64877
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Baseline (vscode)

Cumulative result (merge-base 3789ddb vs HEAD, vscode, interleaved runs, n=6)

Experiments

1. dirty.SyncMap.LoadClean fast path in snapshotFSBuilder — COMMITTED (0a35842; benchmarks in dd354e654af)

2. parseTask hot/cold split (compiler/filesparser.go) — COMMITTED (cea07f4)

3. Concurrent directory prefetch in vfsmatch — COMMITTED (39911ff)

4. sourceFS seen-file tracking + overlayFS no-clone — COMMITTED (039e5dd)

5. packagejson.InfoCache cheap Clone — COMMITTED (14e9882; RWMutex variant squashed away)

6. autoimport Export 248 → 192 B — COMMITTED (b975755)

7. tsoptions extension-priority sibling keys — COMMITTED (c09c9b0)

8. Module resolution: resolve candidate once — COMMITTED (de88374)

9. tspath leading ./ / ../ fast path — COMMITTED (9496c1e)

10. parseTask references resolution PackageId — COMMITTED (02e334f)

11. Co-allocated referenced-file include reasons — COMMITTED (570e356)

12. parallelWorkGroup.Queue wrapper closure — COMMITTED (d248609)

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Cumulative result (merge-base `3789ddb` vs HEAD, vscode, interleaved runs, n=6)

1. `dirty.SyncMap.LoadClean` fast path in snapshotFSBuilder — COMMITTED (`0a35842`; benchmarks in dd354e654af)

2. parseTask hot/cold split (compiler/filesparser.go) — COMMITTED (`cea07f4`)

3. Concurrent directory prefetch in vfsmatch — COMMITTED (`39911ff`)

4. sourceFS seen-file tracking + overlayFS no-clone — COMMITTED (`039e5dd`)

5. packagejson.InfoCache cheap Clone — COMMITTED (`14e9882`; RWMutex variant squashed away)

6. autoimport `Export` 248 → 192 B — COMMITTED (`b975755`)

7. tsoptions extension-priority sibling keys — COMMITTED (`c09c9b0`)

8. Module resolution: resolve candidate once — COMMITTED (`de88374`)

9. tspath leading `./` / `../` fast path — COMMITTED (`9496c1e`)

10. parseTask references resolution PackageId — COMMITTED (`02e334f`)

11. Co-allocated referenced-file include reasons — COMMITTED (`570e356`)

12. `parallelWorkGroup.Queue` wrapper closure — COMMITTED (`d248609`)

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