Slow output rendering in terminal when ConPty is enabled

[janegilring]

Issue Type: Performance Issue

When running a command which produces a long list of output, the rendering in the terminal is very slow. Here is an example running Get-Process in PowerShell Core 6.2:
Get-Process
Get-History -Count 1 | Format-Table Commandline,Duration

CommandLine Duration
Get-Process 00:00:26.3913173

The same command run with ConPty disabled:
CommandLine Duration
Get-Process 00:00:00.7955070

The same command run outside of VS Code (from pwsh.exe):
CommandLine Duration
Get-Process 00:00:00.7453859

VS Code version: Code 1.33.1 (51b0b28, 2019-04-11T08:27:14.102Z)
OS version: Windows_NT x64 10.0.18362

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz (4 x 2808)
GPU Status	2d_canvas: enabled checker_imaging: disabled_off flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: enabled surface_synchronization: enabled_on video_decode: enabled webgl: enabled webgl2: enabled
Memory (System)	15.93GB (3.46GB free)
Process Argv
Screen Reader	no
VM	0%

Process Info

CPU %	Mem MB	   PID	Process
    2	   108	  7724	code main
    0	   416	  3464	   window (undefined)
    0	   327	  6212	   window (profile.ps1 - WindowsPowerShell - Visual Studio Code)
    0	     5	  6684	     console-window-host (Windows internal process)
    0	   204	  8780	     "C:\Program Files\PowerShell\6\pwsh.exe" -NoProfile -NonInteractive -ExecutionPolicy Bypass -Command "& 'C:\Users\janring\.vscode\extensions\ms-vscode.powershell-1.12.1\modules\PowerShellEditorServices\Start-EditorServices.ps1' -HostName 'Visual Studio Code Host' -HostProfileId 'Microsoft.VSCode' -HostVersion '1.12.1' -AdditionalModules @('PowerShellEditorServices.VSCode') -BundledModulesPath 'C:\Users\janring\.vscode\extensions\ms-vscode.powershell-1.12.1\modules' -EnableConsoleRepl -LogLevel 'Normal' -LogPath 'C:\Users\janring\.vscode\extensions\ms-vscode.powershell-1.12.1\logs\1555734840-ba0f8cd2-2191-4408-9d02-d80b8966f56f1555702179639\EditorServices.log' -SessionDetailsPath 'C:\Users\janring\.vscode\extensions\ms-vscode.powershell-1.12.1\sessions\PSES-VSCode-7724-999400' -FeatureFlags @()"
    0	   177	  8924	     extensionHost
    0	    29	 15300	       "C:\Users\janring\AppData\Local\Programs\Microsoft VS Code\Code.exe" "c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\extensions\json-language-features\server\dist\jsonServerMain" --node-ipc --clientProcessId=8924
    0	    30	 17632	       electron_node server.js 
    0	    26	 18288	       electron_node server.js 
    0	    12	 14404	     watcherService 
    0	     5	 13384	       console-window-host (Windows internal process)
    0	    11	 16380	     electron-crash-reporter
    0	     3	 17676	     C:\WINDOWS\System32\cmd.exe
    0	     6	 18444	     console-window-host (Windows internal process)
    0	    70	 12168	   shared-process
    3	    60	 17864	   window (Issue Reporter)
    3	   488	 18156	   gpu-process

Workspace Info

|  Window (profile.ps1 - WindowsPowerShell - Visual Studio Code)
|    Folder (WindowsPowerShell): 1353 files
|      File types: ps1(1126) psm1(33) psd1(31) xml(27) ps1xml(22) txt(18)
|                  csv(17) json(10) png(10) md(8)
|      Conf files: sln(1);

Extensions (34)

Extension	Author (truncated)	Version
swagger-viewer	Arj	2.2.2
armsnippet	art	0.7.0
bracket-pair-colorizer-2	Coe	0.0.28
vscode-markdownlint	Dav	0.26.0
vscode-instant-markdown	dba	1.4.3
githistory	don	0.4.6
vscode-pandoc	Dou	0.0.8
gitlens	eam	9.6.2
powershellprotools	iro	4.4.0
vscode-peacock	joh	2.1.0
terraform	mau	1.3.9
rainbow-csv	mec	1.0.0
azure-pipelines	ms-	1.147.2
vscode-azureappservice	ms-	0.13.0
vscode-azurefunctions	ms-	0.16.0
vscode-azurestorage	ms-	0.7.0
vscode-azureterraform	ms-	0.2.3
vscode-logicapps	ms-	0.1.17
python	ms-	2019.3.6558
azure-account	ms-	0.8.2
azurecli	ms-	0.4.4
powershell	ms-	1.12.1
vsliveshare	ms-	1.0.67
team	ms-	1.149.2
azurerm-vscode-tools	msa	0.5.0
indent-rainbow	ode	7.4.0
vscode-docker	Pet	0.6.1
material-icon-theme	PKi	3.7.0
vscode-coverage-gutters	rya	2.3.1
code-settings-sync	Sha	3.2.9
guides	spy	0.9.3
shell-launcher	Tyr	0.3.0
gitblame	wad	2.7.0
markdown-all-in-one	yzh	2.2.0

(1 theme extensions excluded)

[janegilring]

I tried to enable escape sequence logging, and see the following in the console in the developer tools when re-running Get-Process:
c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:1084 Unknown CSI code: {collect: "", params: Array(1), flag: "C"}
Terminal.error @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:1084
(anonymous) @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\InputHandler.js:73
EscapeSequenceParser.parse @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\EscapeSequenceParser.js:407
InputHandler.parse @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\InputHandler.js:191
Terminal._innerWrite @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:893
(anonymous) @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:873
setTimeout (async)
Terminal.write @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:872
Terminal.write @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\public\Terminal.js:125
_onProcessData @ terminalInstance.ts:928
_processManager._processManager.onProcessData.e @ terminalInstance.ts:429
fire @ event.ts:584
l.onProcessData.e @ terminalProcessManager.ts:186
fire @ event.ts:584
_ptyProcess.on.e @ terminalProcess.ts:79
emit @ events.js:187
addChunk @ _stream_readable.js:279
readableAddChunk @ _stream_readable.js:260
Readable.push @ _stream_readable.js:219
onread @ net.js:636
c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:1084 Unknown CSI code: {collect: "", params: Array(1), flag: "X"}
Terminal.error @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:1084
(anonymous) @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\InputHandler.js:73
EscapeSequenceParser.parse @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\EscapeSequenceParser.js:407
InputHandler.parse @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\InputHandler.js:191
Terminal._innerWrite @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:893
(anonymous) @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:873
setTimeout (async)
Terminal.write @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:872
Terminal.write @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\public\Terminal.js:125
_onProcessData @ terminalInstance.ts:928
_processManager._processManager.onProcessData.e @ terminalInstance.ts:429
fire @ event.ts:584
l.onProcessData.e @ terminalProcessManager.ts:186
fire @ event.ts:584
_ptyProcess.on.e @ terminalProcess.ts:79
emit @ events.js:187
addChunk @ _stream_readable.js:279
readableAddChunk @ _stream_readable.js:260
Readable.push @ _stream_readable.js:219
onread @ net.js:636
c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:1084 Unknown CSI code: {collect: "", params: Array(1), flag: "C"}
Terminal.error @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:1084
(anonymous) @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\InputHandler.js:73
EscapeSequenceParser.parse @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\EscapeSequenceParser.js:407
InputHandler.parse @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\InputHandler.js:191
Terminal._innerWrite @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:893
(anonymous) @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:873
setTimeout (async)
Terminal.write @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:872
Terminal.write @ c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\public\Terminal.js:125
_onProcessData @ terminalInstance.ts:928
_processManager._processManager.onProcessData.e @ terminalInstance.ts:429
fire @ event.ts:584
l.onProcessData.e @ terminalProcessManager.ts:186
fire @ event.ts:584
_ptyProcess.on.e @ terminalProcess.ts:79
emit @ events.js:187
addChunk @ _stream_readable.js:279
readableAddChunk @ _stream_readable.js:260
Readable.push @ _stream_readable.js:219
onread @ net.js:636
c:\Users\janring\AppData\Local\Programs\Microsoft VS Code\resources\app\node_modules.asar\vscode-xterm\lib\Terminal.js:1084 Unknown CSI code: {collect: "", params: Array(1), flag: "X"}

[Tyriar]

I could reproduce this on my work machine, for me it was an issue with GPU/canvas drawing performance and the simple fix it to add this to your settings:

"terminal.integrated.rendererType": "dom"

It's meant to switch this setting automatically if you haven't set it already and this sort of slow down happens 🤔

https://github.com/Microsoft/vscode/blob/50c9a782ad2cf3b1b662966455187f8a9ec41bac/src/vs/workbench/contrib/terminal/browser/terminalInstance.ts#L646

Does that fix your problem?

[janegilring]

The setting was already present when I tried to add it. However, it might have been added automatically, as performance seems to be much improved now.

CommandLine Duration
gps 00:00:05.8818659

I haven`t done anything besides closing/re-opening VS Code a few times during testing.

[wjrogers]

I've been having a similar problem for a couple VS Code versions, I think all since conpty support landed. Today, I tried the dom renderer setting, and it fixed the slow terminal output. FWIW, I often use Code via RDP, but I'm pretty sure I observed the same problem on the same machine working locally.

Code 1.35.0
Windows 10 Pro 1903 build 18362.113

[Tyriar]

This was also reported in #74914, I think the root cause is the event loop related stuff in #74620