Massive CPU spike coming from pylance

[RealTachyon]

Type: Bug
I'm experiencing a huge CPU spike when I'm simply adding text to the code I'm working on.
The CPU usage jumps from effectively 0% to 50-100%

In the Process explorer, the only process I could see rising was
electron-nodejs (bundle.js)

Extension version: 2025.10.4
VS Code version: Code 1.107.0 (618725e67565b290ba4da6fe2d29f8fa1d4e3622, 2025-12-10T07:43:47.883Z)
OS version: Windows_NT x64 10.0.19045
Modes:

System Added Logs

2025-12-17 20:18:51.919 [info] Client: Pylance client (2025.10.4) started with python extension (2025.20.0)
2025-12-17 20:19:04.171 [info] (24696): Server root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 20:19:04.180 [info] (24696): Pylance language server 2025.10.4 (pyright version 1.1.407, commit 906e40aa) starting
2025-12-17 20:19:04.217 [info] (24696): Starting service instance "<USER>_blender" for workspace "l:\Programming\Python\Projects\<USER>_blender"
2025-12-17 20:19:19.475 [info] (24696): Loading background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js into file:///l%3A/Programming/Python/Projects/<USER>_blender...
2025-12-17 20:19:20.582 [info] (24696): FG(<USER>_blender): Loading pyproject.toml file at l:\Programming\Python\Projects\<USER>_blender\pyproject.toml
2025-12-17 20:19:20.881 [info] (24696): FG(<USER>_blender): Setting environmentName for service "<USER>_blender": "3.11.0 (<USER>-blender-py3.11 venv)"
2025-12-17 20:19:20.900 [info] (24696): FG(<USER>_blender): Setting pythonPath for service "<USER>_blender": "L:\Programming\Python\Projects\<USER>_blender\.venv\Scripts\python.exe"
2025-12-17 20:19:20.939 [info] (24696): FG(<USER>_blender): No include entries specified; assuming l:\Programming\Python\Projects\<USER>_blender
2025-12-17 20:19:22.981 [info] (24696): FG(<USER>_blender): Assuming Python version 3.11.0.final.0
2025-12-17 20:19:33.219 [info] (24696): FG(<USER>_blender): Found 1431 source files
2025-12-17 20:19:33.583 [info] (24696): BG(<USER>_blender): Loaded external background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js. 
2025-12-17 20:19:33.591 [info] (24696): PQ(<USER>_blender): Priority queue background worker(2) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 20:19:33.592 [info] (24696): PQ(<USER>_blender): Priority queue background worker(2) started
2025-12-17 20:19:33.593 [info] (24696): Settings have not changed. Skipping update.
2025-12-17 20:19:35.052 [info] (24696): Starting Mcp server id:5518 ...
2025-12-17 20:19:38.840 [info] (24696): IDX(<USER>_blender): Indexer background runner(3) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist (index)
2025-12-17 20:19:38.845 [info] (24696): IDX(<USER>_blender): Indexing(3) started
2025-12-17 20:19:44.408 [info] (24696): BG(<USER>_blender): Long operation: parsing: file:///l%3A/Programming/Python/Projects/<USER>_blender/.venv/Lib/site-packages/bpy/types/__init__.pyi (5410ms)
2025-12-17 20:19:46.834 [info] (24696): BG(<USER>_blender): Long operation: binding: file:///l%3A/Programming/Python/Projects/<USER>_blender/.venv/Lib/site-packages/bpy/types/__init__.pyi (2405ms)
2025-12-17 20:19:50.407 [info] (24696): IDX(<USER>_blender): Long operation: scan packages file:///l%3A/Programming/Python/Projects/<USER>_blender (9255ms)
2025-12-17 20:19:50.410 [info] (24696): IDX(<USER>_blender): scanned(3) 339 files over 1 exec env
2025-12-17 20:19:50.824 [info] (24696): BG(<USER>_blender): Long operation: SemanticTokens range 0:0 - 106:34 at file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/ui/panels/collection_property_drawing/Draw_Collection_Property_Element_UI.py (15277ms)
2025-12-17 20:20:01.400 [info] (24696): IDX(<USER>_blender): indexed(3) 339 files over 1 exec env
2025-12-17 20:20:01.413 [info] (24696): IDX(<USER>_blender): Indexing finished(3).
2025-12-17 20:20:38.830 [info] (24696): BG(<USER>_blender): Long operation: checking: file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/commands/renaming/specific/lower_names_in_container.py (3472ms)
2025-12-17 20:20:38.831 [info] (24696): BG(<USER>_blender): Long operation: analyzing: file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/commands/renaming/specific/lower_names_in_container.py (3475ms)
2025-12-17 20:20:44.588 [info] (24696): BG(<USER>_blender): Long operation: checking: file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/higher_level/hyper_bone.py (2584ms)
2025-12-17 20:20:44.589 [info] (24696): BG(<USER>_blender): Long operation: analyzing: file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/higher_level/hyper_bone.py (2585ms)
2025-12-17 20:33:02.894 [info] (24696): Starting service instance "<default>" for workspace ""
2025-12-17 20:33:02.895 [info] (24696): Loading background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js into ...
2025-12-17 20:33:02.976 [info] (24696): FG(<default>): Setting environmentName for service "<default>": "3.11.0 (<USER>-blender-py3.11 venv)"
2025-12-17 20:33:02.976 [info] (24696): FG(<default>): Setting pythonPath for service "<default>": "l:\Programming\Python\Projects\<USER>_blender\.venv\Scripts\python.exe"
2025-12-17 20:33:02.977 [info] (24696): FG(<default>): No include entries specified; assuming \<default workspace root>
2025-12-17 20:33:03.092 [info] (24696): FG(<default>): Assuming Python version 3.11.0.final.0
2025-12-17 20:33:03.341 [error] (24696): FG(<default>): File or directory "\<default workspace root>" does not exist.
2025-12-17 20:33:03.341 [info] (24696): FG(<default>): No source files found.
2025-12-17 20:33:03.717 [info] (24696): PQ(<default>): Priority queue background worker(5) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 20:33:03.718 [info] (24696): PQ(<default>): Priority queue background worker(5) started
2025-12-17 20:33:04.059 [info] (24696): BG(<default>): Loaded external background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js. 
2025-12-17 20:47:21.452 [info] (24696): FG(<USER>_blender): Found 1432 source files
2025-12-17 20:47:32.175 [error] Unhandled Rejection in Pylance: A [Error]: request cancelled
2025-12-17 20:47:32.176 [error]     at t.throwIfCancellationRequested (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\pyright.bundle.js:1:2396887)
2025-12-17 20:47:32.176 [error]     at _0x33b4cd._throwIfOutOfDate (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:587355)
2025-12-17 20:47:32.177 [error]     at _0x33b4cd.getSourceMapper (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:574316)
2025-12-17 20:47:32.177 [error]     at new _0x4e1586 (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:1888279)
2025-12-17 20:47:32.177 [error]     at new _0x1a90a0 (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:1088942)
2025-12-17 20:47:32.177 [error]     at c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:2391281
2025-12-17 20:47:32.177 [error]     at _0x47daa6 (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:1633668)
2025-12-17 20:47:32.177 [error]     at c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:2391170
2025-12-17 20:47:32.177 [error]     at _0x33b4cd.runAsync (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:573308)
2025-12-17 20:47:32.177 [error]     at _0x1a7312._runCoreAsync (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:365268)
2025-12-17 20:47:32.177 [error]     at _0x35ea16.handleHover (c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\server.bundle.js:1:2390810)
2025-12-17 20:47:32.177 [error]     at c:\Users\<USER>\.vscode\extensions\ms-python.vscode-pylance-2025.10.4\dist\vendor.bundle.js:2:2210000 {
2025-12-17 20:47:32.177 [error]   code: -32800,
2025-12-17 20:47:32.178 [error]   data: undefined,
2025-12-17 20:47:32.178 [error]   isTypeCacheInvalid: false
2025-12-17 20:47:32.178 [error] }
2025-12-17 20:47:32.808 [error] Server process exited with code 10.
2025-12-17 20:47:32.827 [info] Connection to server got closed. Server will restart.
2025-12-17 20:47:35.475 [info] (26260): Server root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 20:47:35.487 [info] (26260): Pylance language server 2025.10.4 (pyright version 1.1.407, commit 906e40aa) starting
2025-12-17 20:47:35.518 [info] (26260): Starting service instance "<USER>_blender" for workspace "l:\Programming\Python\Projects\<USER>_blender"
2025-12-17 20:47:35.730 [info] Client: Failed to provide MCP server definitions: Error: Unhandled method python/mcpPort
2025-12-17 20:47:35.951 [info] (26260): FG(<USER>_blender): Loading pyproject.toml file at l:\Programming\Python\Projects\<USER>_blender\pyproject.toml
2025-12-17 20:47:36.029 [info] (26260): FG(<USER>_blender): Setting environmentName for service "<USER>_blender": "3.11.0 (<USER>-blender-py3.11 venv)"
2025-12-17 20:47:36.030 [info] (26260): FG(<USER>_blender): Setting pythonPath for service "<USER>_blender": "L:\Programming\Python\Projects\<USER>_blender\.venv\Scripts\python.exe"
2025-12-17 20:47:36.032 [info] (26260): FG(<USER>_blender): No include entries specified; assuming l:\Programming\Python\Projects\<USER>_blender
2025-12-17 20:47:36.638 [info] (26260): FG(<USER>_blender): Assuming Python version 3.11.0.final.0
2025-12-17 20:47:40.355 [info] (26260): FG(<USER>_blender): Found 1432 source files
2025-12-17 20:47:40.552 [info] (26260): PQ(<USER>_blender): Priority queue background worker(2) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 20:47:40.553 [info] (26260): PQ(<USER>_blender): Priority queue background worker(2) started
2025-12-17 20:47:40.559 [info] (26260): Settings have not changed. Skipping update.
2025-12-17 20:47:44.359 [info] (26260): IDX(<USER>_blender): Indexer background runner(3) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist (index)
2025-12-17 20:47:44.359 [info] (26260): IDX(<USER>_blender): Indexing(3) started
2025-12-17 20:47:44.980 [info] (26260): BG(<USER>_blender): Long operation: SemanticTokens range 0:0 - 94:42 at file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/ui/panels/collection_property_drawing/Draw_Collection_Property_Element_UI.py (2937ms)
2025-12-17 20:47:46.969 [info] (26260): IDX(<USER>_blender): scanned(3) 339 files over 1 exec env
2025-12-17 20:47:47.518 [info] (26260): IDX(<USER>_blender): indexed(3) 339 files over 1 exec env
2025-12-17 20:47:47.651 [info] (26260): IDX(<USER>_blender): Indexing finished(3).
2025-12-17 20:48:52.138 [info] (26260): Starting service instance "<default>" for workspace ""
2025-12-17 20:48:52.219 [info] (26260): FG(<default>): Setting environmentName for service "<default>": "3.11.0 (<USER>-blender-py3.11 venv)"
2025-12-17 20:48:52.220 [info] (26260): FG(<default>): Setting pythonPath for service "<default>": "l:\Programming\Python\Projects\<USER>_blender\.venv\Scripts\python.exe"
2025-12-17 20:48:52.220 [info] (26260): FG(<default>): No include entries specified; assuming \<default workspace root>
2025-12-17 20:48:52.361 [info] (26260): FG(<default>): Assuming Python version 3.11.0.final.0
2025-12-17 20:48:52.653 [error] (26260): FG(<default>): File or directory "\<default workspace root>" does not exist.
2025-12-17 20:48:52.653 [info] (26260): FG(<default>): No source files found.
2025-12-17 20:48:53.200 [info] (26260): PQ(<default>): Priority queue background worker(5) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 20:48:53.202 [info] (26260): PQ(<default>): Priority queue background worker(5) started
2025-12-17 20:56:27.480 [info] (26260): FG(<USER>_blender): Found 1432 source files
2025-12-17 21:00:49.305 [info] (26260): Settings have not changed. Skipping update.
2025-12-17 21:00:49.306 [info] (26260): Settings have not changed. Skipping update.
2025-12-17 21:00:50.199 [info] (26260): IDX(<USER>_blender): Indexer background runner(6) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist (refresh)
2025-12-17 21:00:50.200 [info] (26260): IDX(<USER>_blender): Indexing(6) started
2025-12-17 21:00:51.897 [info] (26260): IDX(<USER>_blender): scanned(6) 339 files over 1 exec env
2025-12-17 21:00:52.411 [info] (26260): IDX(<USER>_blender): indexed(6) 339 files over 1 exec env
2025-12-17 21:00:52.527 [info] (26260): IDX(<USER>_blender): Indexing finished(6).
2025-12-17 21:01:31.309 [info] Client: Pylance client (2025.10.4) started with python extension (2025.20.1)
2025-12-17 21:01:32.168 [info] (53640): Server root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 21:01:32.168 [info] (53640): Pylance language server 2025.10.4 (pyright version 1.1.407, commit 906e40aa) starting
2025-12-17 21:01:32.179 [info] (53640): Starting service instance "<USER>_blender" for workspace "l:\Programming\Python\Projects\<USER>_blender"
2025-12-17 21:01:33.293 [info] (53640): Loading background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js into file:///l%3A/Programming/Python/Projects/<USER>_blender...
2025-12-17 21:01:33.389 [info] (53640): FG(<USER>_blender): Loading pyproject.toml file at l:\Programming\Python\Projects\<USER>_blender\pyproject.toml
2025-12-17 21:01:33.408 [info] (53640): FG(<USER>_blender): Setting environmentName for service "<USER>_blender": "3.11.0 (<USER>-blender-py3.11 venv)"
2025-12-17 21:01:33.411 [info] (53640): FG(<USER>_blender): Setting pythonPath for service "<USER>_blender": "L:\Programming\Python\Projects\<USER>_blender\.venv\Scripts\python.exe"
2025-12-17 21:01:33.412 [info] (53640): FG(<USER>_blender): No include entries specified; assuming l:\Programming\Python\Projects\<USER>_blender
2025-12-17 21:01:33.536 [info] (53640): FG(<USER>_blender): Assuming Python version 3.11.0.final.0
2025-12-17 21:01:34.711 [info] (53640): FG(<USER>_blender): Found 1432 source files
2025-12-17 21:01:34.742 [info] (53640): BG(<USER>_blender): Loaded external background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js. 
2025-12-17 21:01:34.742 [info] (53640): PQ(<USER>_blender): Priority queue background worker(2) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 21:01:34.742 [info] (53640): PQ(<USER>_blender): Priority queue background worker(2) started
2025-12-17 21:01:34.743 [info] (53640): Settings have not changed. Skipping update.
2025-12-17 21:01:34.755 [info] (53640): Starting Mcp server id:4380 ...
2025-12-17 21:01:35.606 [info] (53640): IDX(<USER>_blender): Indexer background runner(3) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist (index)
2025-12-17 21:01:35.606 [info] (53640): IDX(<USER>_blender): Indexing(3) started
2025-12-17 21:01:37.264 [info] (53640): BG(<USER>_blender): Long operation: checking: file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/ui/panels/collection_property_drawing/draw_collection_properties_ui.py (2074ms)
2025-12-17 21:01:37.265 [info] (53640): BG(<USER>_blender): Long operation: analyzing: file:///l%3A/Programming/Python/Projects/<USER>_blender/<USER>_blender/ui/panels/collection_property_drawing/draw_collection_properties_ui.py (2357ms)
2025-12-17 21:01:37.595 [info] (53640): IDX(<USER>_blender): scanned(3) 339 files over 1 exec env
2025-12-17 21:01:38.116 [info] (53640): IDX(<USER>_blender): indexed(3) 339 files over 1 exec env
2025-12-17 21:01:38.248 [info] (53640): IDX(<USER>_blender): Indexing finished(3).
2025-12-17 21:08:04.699 [info] (53640): Starting service instance "<default>" for workspace ""
2025-12-17 21:08:04.700 [info] (53640): Loading background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js into ...
2025-12-17 21:08:04.777 [info] (53640): FG(<default>): Setting environmentName for service "<default>": "3.11.0 (<USER>-blender-py3.11 venv)"
2025-12-17 21:08:04.778 [info] (53640): FG(<default>): Setting pythonPath for service "<default>": "l:\Programming\Python\Projects\<USER>_blender\.venv\Scripts\python.exe"
2025-12-17 21:08:04.779 [info] (53640): FG(<default>): No include entries specified; assuming \<default workspace root>
2025-12-17 21:08:04.896 [info] (53640): FG(<default>): Assuming Python version 3.11.0.final.0
2025-12-17 21:08:05.213 [error] (53640): FG(<default>): File or directory "\<default workspace root>" does not exist.
2025-12-17 21:08:05.213 [info] (53640): FG(<default>): No source files found.
2025-12-17 21:08:05.509 [info] (53640): PQ(<default>): Priority queue background worker(5) root directory: file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist
2025-12-17 21:08:05.511 [info] (53640): PQ(<default>): Priority queue background worker(5) started
2025-12-17 21:08:05.860 [info] (53640): BG(<default>): Loaded external background bundle file:///c%3A/Users/<USER>/.vscode/extensions/ms-python.vscode-pylance-2025.10.4/dist/copilot-background.bundle.js. 

System Info

Item	Value
CPUs	AMD Ryzen Threadripper 2970WX 24-Core Processor (48 x 2994)
GPU Status	2d_canvas: enabled direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off trees_in_viz: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	undefined
Memory (System)	63.88GB (30.29GB free)
Process Argv	--crash-reporter-id 0f924fbb-88c9-44bf-bd09-f8e30396fdf9
Screen Reader	no
VM	0%

A/B Experiments

vsliv368:30146709
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
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pythonrdcb7:31342333
6518g693:31436602
aj953862:31281341
b6b4d950:31327385
nes-set-on:31351930
6abeh943:31336334
envsdeactivate2:31353495
cloudbuttont:31379625
todos-1:31405332
3efgi100_wstrepl:31403338
trigger-command-fix:31379601
use-responses-api:31390855
d5i5i512:31428709
ec5jj548:31422691
terminalsuggestenabled:31431119
cp_cls_c_966_ss:31435507
c0683394:31419495
478ah919:31426797
a5gib710:31434435
7a04d226_do_not_restore_last_panel_session:31434268
anthropic_thinking_t:31432745
cp_cls_c_1081:31433293

[github-actions]

Hi @RealTachyon, I'm an AI Support assistant here to help with your issue. While the team reviews your request, I wanted to provide some possible tips and documentation that might help you in the meantime.

---

Potential Duplicate Issues – These issues may be duplicates of your report, but may differ in some of the details.

• Pylance Extension High CPU – Python extension with Pylance causes high CPU load on file save or while typing. Pylance Extension High CPU #2414
• Pylance causes extensive CPU usage – Persistent CPU spikes after opening large file. Pylance causes extensive CPU usage #4504

---

Potential Workarounds:

• Exclude large directories from analysis:

  "python.analysis.exclude": {
    "**/site-packages": true,
    "**/node_modules": true
  }

• Disable library code analysis:

  "python.analysis.useLibraryCodeForTypes": false

• Revert to an earlier Pylance version (prior to the aggressive indexer changes in 2025).

---

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[rchiodo]

The advice given by the AI is the only thing to be done here. When you change code in a file, it affects all of the files that import that file. This can cause a whole bunch of analysis to occur. It really depends upon the structure of your code and how you have your settings specified.

CPU usage isn't something we generally try to minimize. Time for operations is more important. If that CPU spike is causing something to take too long, we'd want to investigate. Otherwise, this should be by design.

[RealTachyon]

The settings as given by the AI were already part of my setup.

And this is a new problem that has only manifested itself today. If this was a thing in the past, then it at least didn't make itself known. But here it actually does result in an issue, as 100% CPU usage means that every program running (VSCode included) is frozen for several seconds.
This does sound like a design issue to me.

[rchiodo]

CPU at 100% shouldn't freeze VS code. That would be the foreground thread on VS code. Pylance runs in a separate process.

We have a command to track what Pylance is doing. That should show exactly what was in the CPU spike for pylance:

If you run that while the CPU is busy and then Pylance: Stop Profiling it will generate a cpuprofile of pylance and we can see exactly where the CPU (at least for Pylance) is being spent.

[RealTachyon]

I've followed these steps.
There is no message box opening up, telling me where the output has been saved.
This seems like a bug in itself.

I have navigated over to here
C:\Users\USER\AppData\Local\Temp\pyright-42704-O0dEe9N0O6br
Which was the newest generated folder when I ran the profiling.

Here are the files within it

pylance_2025.10.4_bg_PROJECT_id_0.cpuprofile
pylance_2025.10.4_bg_PROJECT_id_1.cpuprofile
pylance_2025.10.4_bg_PROJECT_id_2.cpuprofile
pylance_2025.10.4_bg_PROJECT_id_3.cpuprofile
pylance_2025.10.4_fg_id_0.cpuprofile
pylance_2025.10.4_fg_id_1.cpuprofile
pylance_2025.10.4_fg_id_2.cpuprofile
pylance_2025.10.4_fg_id_3.cpuprofile

[rchiodo]

For your largest BG profile, it was only half a second of time computing diagnostics and semantic tokens. That's normal:

The FG thread (where you would see some slow down in the UI on say completions or hover) in your worst scenario is basically doing the FG work to handle diagnostics

So AFAICT, Pylance is not really using the CPU.

What's the behavior you're seeing when the CPU spikes? Is VS code unresponsive?

[RealTachyon]

That's strange.
VSCode becomes unresponsive for several seconds, but this behavior can also be seen on other programs, like Firefox.
If the profiling didn't see anything out of the ordinary, maybe it didn't catch the actual culprit? Is there any other profiling I can run to see check what's going on?

I can consistently trigger the slowdown when I save a file.

[rchiodo]

Ah saving a file triggers things in VS code. Extensions can run code on save. That could be us too or some other extension or VS code itself. Our cpu profiling here was just our server, it's possible something in the extension is the problem, or some other extension is running code on save.

VS code has a way to profile extensions:

Run "Developer: Show Running Extensions"

That should cause this window to open:

On the far right there's a toolbar of sorts:

The little black dot starts profiling the extension host.

Do that and then try saving.

[RealTachyon]

The spike still happens consistently during saving, and this is the result of the profiling.

Git seems to be highest, but is still at 71ms. That number still seems very low to be actually causing the lag.

[rchiodo]

It could be VS code itself then.

You could try the same thing but disable all extensions and see if the problem goes away.

[rchiodo]

VS code also has its own profiler. Just open Developer Tools and pick the Performance tab.

Developer Tools : Show Process Explorer should also show CPU usage on a per VS code process basis.