Version 3.5.0 - high CPU usage after spewing a lot of scrollback

[Chap Harrison]

Just installed 3.5.0. When I run a program that spits out around 10M of data, performance becomes very sluggish and one core is steadily consuming 50% CPU. This persists after I clear scrollback buffer and only stops when I close the tab containing the session. 

MacBook Air M1 2020, macOS 14.5. 

Anyone else corroborate this?

[George Nachman]

Can you grab a sample? Instructions here: https://gitlab.com/gnachman/iterm2/-/wikis/HowToSample

Please file an issue with it.

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[Chap Harrison]

https://gitlab.com/gnachman/iterm2/-/issues/11496

[cpi...@gmail.com]

2019 Macbook Pro here running Monterey and I see 100% CPU usage even after closing ALL TABS. It finally died down after a minute. I already disabled disk logging as I haven't been need it. AFAIK AI stuff is disabled. What's is iTerm doing while NOTHING IS HAPPENING (8 tabs but none yet reconnected to a session when it was eating 100% cpu after a fresh restart.)   This is crazy. Good thing Terminal is semi useful cuz I may have to revert until this is fixed.

[George Nachman]

Please see my instructions below about how to sample the app.

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[Eric]

Hello, I have abnormal CPU use too, only 9 windows open, none running any process

[George Nachman]

That sample doesn’t show very high utilization - just the GPU renderer using < 10% or so. Maybe try to catch a sample again?

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[Eric Doughty-Papassideris]

It hovers around 15-30%, thing is this is completely idle, there is nothing running, all windows are waiting for input, so anything above 0 I'd call abnormal.

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[George Nachman]

It may be that you’re hitting some pathological case in the GPU renderer. I’m curious, does turning off Settings > General > Magic > GPU Renderer cause CPU utilization to down to near 0?

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[Eric Doughty-Papassideris]

Thanks, this reduced use when idle to about 5% (it's stabilised there, ramped up after restart, but seems happy between 4.5 and 6), I'm attaching another sample, thanks for your help :)

[George Nachman]

The remaining usage is largely related to a tableview of some sort. My best guess is that it’s something in the toolbelt, unless you have a popup like pasteboard history open. Does closing the toolbelt make it go down? If so let me know which tools you have open and I’ll try to see why they are redrawing themselves excessively.

Commit 35877a841752cd0957f2a42a16559df3feb3f5fa and 5e7a67f08b4d490825c34185b32c4b4cd39a5a15 should fix most of the performance issues in your sample related to timestamps, which was the largest issue.

On Nov 25, 2025 at 5:55:36 PM, Eric Doughty-Papassideris <eric.d...@gmail.com> wrote:

Thanks, this reduced use when idle to about 5% (it's stabilised there, ramped up after restart, but seems happy between 4.5 and 6), I'm attaching another sample, thanks for your help :)

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