pytest runner overrides --dist=worksteal

Type: Performance Issue

Behaviour

pytest runner in the left panel seems to do something like dist=load despite my settings.json, resulting in periodic bottlenecking on slow tests.

Steps to reproduce:

Running my large suite with uv run pytest tests -n auto --dist worksteal saturates CPU and gives long ..... lines undifferentiated by filenames. But execting the runner with settings.json

{
    "python.testing.pytestArgs": [
        "tests",
        "-n", "auto",
        "--dist", "worksteal"
    ],
    "python.testing.unittestEnabled": false,
    "python.testing.pytestEnabled": true
}

produces a long list of FILENAME ..... [PCT%] lines, and repeated bursts of full core saturation interspersed by long stretches of single-core usage in a single suite run.

Diagnostic data

Details

Excerpt from the TEST RESULTS panel:

Running pytest with args: ['-p', 'vscode_pytest', '-n', 'auto', '--dist', 'worksteal', '--rootdir=/home/tbertalan/lake/Projects/ModelCalibration-issue-118', (long list of specific path/file.py::class entries snipped here)
============================= test session starts ==============================
platform linux -- Python 3.12.13, pytest-9.0.3, pluggy-1.6.0
rootdir: /home/tbertalan/lake/Projects/ModelCalibration-issue-118
configfile: pyproject.toml
plugins: cov-7.1.0, xdist-3.8.0, typeguard-2.13.3, jaxtyping-0.3.11, anyio-4.13.0
collected 446 items

tests/test_anp_loader.py ........................................        [  8%]
tests/test_anp_registry.py ..............................                [ 15%]
tests/test_behavior.py .......                                           [ 17%]

vs a (non-vscode) terminal run

tbertalan@swiftie:~/lake/Projects/ModelCalibration-issue-118$ uv run pytest -n auto -p no:slow-first
      Built modelcalibration @ file:///home/tbertalan/lake/Projects/ModelCalibration-issue-118
Uninstalled 1 package in 0.81ms
Installed 1 package in 3ms
============================================================================================== test session starts ==============================================================================================
platform linux -- Python 3.12.13, pytest-9.0.3, pluggy-1.6.0
rootdir: /home/tbertalan/lake/Projects/ModelCalibration-issue-118
configfile: pyproject.toml
testpaths: tests
plugins: cov-7.1.0, xdist-3.8.0, typeguard-2.13.3, jaxtyping-0.3.11, anyio-4.13.0
4 workers [446 items]
...............................................................................................................................................................x.xxx............................x........ [ 45%]
.................x..x.....................................................................Xss............................................................................................................ [ 90%]
............................................

Extension version: 2026.4.0
VS Code version: Code 1.129.1 (8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8, 2026-07-17T15:35:09Z)
OS version: Windows_NT x64 10.0.26200
Modes:
Remote OS version: Linux x64 6.14.0-37-generic

Python version (& distribution if applicable, e.g. Anaconda): 3.13.3.final.0
Type of virtual environment used (e.g. conda, venv, virtualenv, etc.): System
Value of the python.languageServer setting: Default

User Settings


languageServer: "Pylance"

testing
• pytestArgs: "<placeholder>"
• pytestEnabled: true

Installed Extensions

Extension Name	Extension Id	Version
autopep8	ms-	2026.4.0
claude-code	Ant	2.1.215
copilot-chat	Git	0.57.0
debugpy	ms-	2026.6.0
git-graph	mhu	1.30.0
git-worktrees	Git	2.16.0
js-debug	ms-	1.117.0
jsts-chat-features	Typ	0.0.4
jupyter	ms-	2025.9.1
jupyter-renderers	ms-	1.3.0
markdown-all-in-one	yzh	3.6.3
markdown-mermaid	bie	1.32.1
mypy-type-checker	ms-	2026.6.0
pth-viewer	pth	0.0.12
pylint	ms-	2026.6.0
python	ms-	2026.4.0
rainbow-csv	mec	3.24.1
vscode-js-profile-table	ms-	1.0.10
vscode-jupyter-cell-tags	ms-	0.1.9
vscode-jupyter-slideshow	ms-	0.1.6
vscode-markdownlint	Dav	0.61.2
vscode-pull-request-github	Git	0.158.0
vscode-pylance	ms-	2026.2.1
vscode-python-envs	ms-	1.36.0
webm-preview	gso	0.1.2

System Info

Item	Value
CPUs	AMD Ryzen 5 7530U with Radeon Graphics (12 x 1996)
GPU Status	2d_canvas: enabled GPU0: VENDOR= 0x1002, DEVICE=0x15e7 [AMD Radeon (TM) Graphics], DRIVER_VENDOR=AMD, DRIVER_VERSION=31.0.21923.13006 ACTIVE GPU1: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8875 Machine model name: Machine model version: 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 webgpu: enabled webnn: disabled_off
Load (avg)	undefined
Memory (System)	14.83GB (0.10GB free)
Process Argv	--crash-reporter-id 3819bd9c-9640-441a-b637-f0405bc1724f
Screen Reader	no
VM	0%

Item	Value
Remote	SSH: swiftie
OS	Linux x64 6.14.0-37-generic
CPUs	Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz (8 x 4200)
Memory (System)	30.28GB (18.76GB free)
VM	0%

Process Info

CPU %	Mem MB	   PID	Process
    1	   154	  5568	code
    1	   599	  4812	window [2] (settings.json - ModelCalibration-issue-118 [SSH: swiftie] - Visual Studio Code)
    0	   295	  6100	window [1] (tasks.json - Journal - Visual Studio Code)
    0	    24	  8216	   crashpad-handler
    0	    42	 17384	   utility-network-service
    0	   476	 18044	extension-host [2]
    0	     8	 28028	     C:\WINDOWS\system32\wsl.exe -d Ubuntu -e /bin/sh -c "cd '/mnt/c/Users/Tom Bertalan/AppData/Local/Programs/Microsoft VS Code' && /bin/sh"
    0	    13	 10976	       C:\WINDOWS\system32\wsl.exe -d Ubuntu -e /bin/sh -c "cd '/mnt/c/Users/Tom Bertalan/AppData/Local/Programs/Microsoft VS Code' && /bin/sh"
    0	    12	  8400	          --distro-id {0eceac0a-0de7-44db-ab7e-a953bbca12d9} --vm-id {97cfd741-f0f7-4580-b40a-526ebdaf3204} --handle 728 --event 752 --parent 756
    0	    10	 27972	           C:\WINDOWS\system32\conhost.exe 0x4
    0	     8	 15480	       C:\WINDOWS\system32\conhost.exe 0x4
    0	   102	 23492	pty-host
    0	    87	  2248	     C:\WINDOWS\System32\WindowsPowerShell\v1.0\powershell.exe -noexit -command "try { . \"c:\Users\Tom Bertalan\AppData\Local\Programs\Microsoft VS Code\8a7abeba6e\resources\app\out\vs\workbench\contrib\terminal\common\scripts\shellIntegration.ps1\" } catch {}"
    0	    12	 16552	     "c:\Users\Tom Bertalan\AppData\Local\Programs\Microsoft VS Code\8a7abeba6e\resources\app\node_modules.asar.unpacked\node-pty\build\Release\conpty\OpenConsole.exe" --headless --inheritcursor --width 80 --height 30 --signal 0x55c --server 0x54c
    0	    12	 26416	     "c:\Users\Tom Bertalan\AppData\Local\Programs\Microsoft VS Code\8a7abeba6e\resources\app\node_modules.asar.unpacked\node-pty\build\Release\conpty\OpenConsole.exe" --headless --width 80 --height 30 --signal 0x738 --server 0x730
    0	    91	 26528	     C:\WINDOWS\System32\WindowsPowerShell\v1.0\powershell.exe -noexit -command "try { . \"c:\Users\Tom Bertalan\AppData\Local\Programs\Microsoft VS Code\8a7abeba6e\resources\app\out\vs\workbench\contrib\terminal\common\scripts\shellIntegration.ps1\" } catch {}"
    0	     8	 31012	     C:\WINDOWS\System32\cmd.exe /c (type "C:\Users\TOMBER~1\AppData\Local\Temp\vscode-linux-multi-line-command-swiftie-908041203.sh" | "C:\WINDOWS\System32\OpenSSH\ssh.exe" -T -D 57373 swiftie sh) & exit /b 0
    0	    14	 30288	       "C:\WINDOWS\System32\OpenSSH\ssh.exe"  -T -D 57373 swiftie sh
    0	    12	 34920	     "c:\Users\Tom Bertalan\AppData\Local\Programs\Microsoft VS Code\8a7abeba6e\resources\app\node_modules.asar.unpacked\node-pty\build\Release\conpty\OpenConsole.exe" --headless --inheritcursor --width 131 --height 30 --signal 0x62c --server 0x624
    1	   138	 24056	   gpu-process
    0	   359	 28444	extension-host [1]
    0	    66	 10424	     "C:\Users\Tom Bertalan\AppData\Local\Programs\Microsoft VS Code\Code.exe" "c:\Users\Tom Bertalan\AppData\Local\Programs\Microsoft VS Code\8a7abeba6e\resources\app\extensions\json-language-features\server\dist\node\jsonServerMain" --node-ipc --clientProcessId=28444
    0	   388	 24684	     electron-nodejs (bundle.js)
    0	    60	 30452	     electron-nodejs (server.js)
    0	    66	 34296	     "C:\Users\Tom Bertalan\AppData\Roaming\uv\python\cpython-3.14.4-windows-x86_64-none\python.exe" "c:\Users\Tom Bertalan\.vscode\extensions\ms-python.pylint-2026.6.0\bundled\tool\lsp_server.py"
    0	     8	 16588	       C:\WINDOWS\system32\conhost.exe 0x4
    0	    12	 35728	     "c:\Users\Tom Bertalan\.vscode\extensions\ms-python.vscode-python-envs-1.36.0-win32-x64\python-env-tools\bin\pet.exe" server
    0	     7	 30724	       C:\WINDOWS\system32\conhost.exe 0x4
    0	    73	 33612	file-watcher [2]
    0	    86	 34496	file-watcher [1]
    0	    98	 35620	shared-process

Remote: SSH: swiftie
CPU %	Mem MB	   PID	Process
    2	   217	1071813	remote-server
    0	    62	1071850	   ptyHost
    0	     0	1071983	     /bin/bash --init-file /home/tbertalan/.vscode-server/cli/servers/Stable-8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8/server/out/vs/workbench/contrib/terminal/common/scripts/shellIntegration-bash.sh
    0	     0	1072407	     /bin/bash --init-file /home/tbertalan/.vscode-server/cli/servers/Stable-8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8/server/out/vs/workbench/contrib/terminal/common/scripts/shellIntegration-bash.sh
    1	   744	1071856	   extension-host
    0	    62	1072004	     /home/tbertalan/.vscode-server/cli/servers/Stable-8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8/server/node /home/tbertalan/.vscode-server/cli/servers/Stable-8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8/server/extensions/markdown-language-features/dist/serverWorkerMain --node-ipc --clientProcessId=1071856
    0	   155	1072022	     /home/tbertalan/.vscode-server/cli/servers/Stable-8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8/server/node /home/tbertalan/.vscode-server/cli/servers/Stable-8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8/server/extensions/json-language-features/server/dist/node/jsonServerMain --node-ipc --clientProcessId=1071856
    0	     0	1072137	     /home/tbertalan/.vscode-server/extensions/ms-python.vscode-python-envs-1.36.0-linux-x64/python-env-tools/bin/pet server
    0	    31	1072423	     /home/tbertalan/lake/Projects/ModelCalibration-issue-118/.venv/bin/python /home/tbertalan/.vscode-server/extensions/ms-python.autopep8-2026.4.0/bundled/tool/lsp_server.py
    0	   527	1072802	     /home/tbertalan/.vscode-server/cli/servers/Stable-8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8/server/node /home/tbertalan/.vscode-server/extensions/ms-python.vscode-pylance-2026.2.1/dist/server.bundle.js --cancellationReceive=file:bbb338299e1c2b081336cb52f5953bc490540afe89 --node-ipc --clientProcessId=1071856
    0	    62	1071873	   fileWatcher
    0	     0	1073210	   /bin/sh -c /usr/bin/ps -ax -o pid=,ppid=,pcpu=,pmem=,command=
    0	     0	1073211	     /usr/bin/ps -ax -o pid=,ppid=,pcpu=,pmem=,command=

Workspace Info

|  Window (tasks.json - Journal - Visual Studio Code)
|    Folder (Journal): 229 files
|      File types: json(134) md(84) png(4) pdf(3) jpg(1) py(1) gitignore(1)
|                  TAG(1)
|      Conf files: tasks.json(1)
|  Remote: SSH: swiftie|    Folder (ModelCalibration-issue-118): more than 20000 files|      File types: py(7391) pyi(5593) json(3018) pyc(1420) dat(1084) so(159)
|                  txt(132) typed(61) md(46) pxd(46) other(1050)
|      Conf files: dockerfile(1) devcontainer.json(1) github-actions(1)
|      Launch Configs: debugpy(3);

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Eleanor Boyd (@eleanorjboyd)

Eleanor Boyd (@eleanorjboyd) can i work on this

🤖 Thanks for the detailed report. The Test Results log shows that the extension is forwarding both -n auto and --dist worksteal, but the two pasted runs are not directly comparable: the terminal transcript uses uv run, adds -p no:slow-first, omits --dist worksteal, and the reported interpreter versions differ. Could you reproduce with the same selected interpreter and environment in both places, run the exact argument list printed by Test Explorer from a terminal, and share both complete pytest headers plus the Python Testing output log and any PYTEST_XDIST_AUTO_NUM_WORKERS value? This will show whether xdist is creating workers and whether the extension's auto-worker hook is reducing their count. Issues marked info-needed automatically close after 30 days without a reply.

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pytest runner overrides --dist=worksteal #26051

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pytest runner overrides --dist=worksteal #26051

Description

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Steps to reproduce:

Diagnostic data

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mohityadav8 commented on Jul 21, 2026

eleanorjboyd commented on Sep 23, 2026

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