most recent ghostty (a lot) slower than 1.1.3 was for some basic operations like cursor reading - and slower over time too (macos at least)

[ldemailly]

Issue Description

Running fps is slower in my setup than 1.1.3 was and gets slightly slower over time (eg 25k fps down to 20 in a few minutes)

See repro for something simpler

Also some more details in https://discord.com/channels/1005603569187160125/1426326165370441849

Expected Behavior

latest ghostty not significantly slower than 1.1.3 and not degrading over time

Actual Behavior

significantly slower (and degrading over time)

Reproduction Steps

run github.com/ldemailly/go-scratch/windows_terminal_issue

go install github.com/ldemailly/go-scratch/windows_terminal_issue@latest

time windows_terminal_issue

(sorry for the name but that simplest code happened to have been used some month back to demonstrate a critical bug in windows terminal (it hanged, while here it's just slow(er)))

Also fortio.org/terminal/fps for the "over time slow down" part

1.1.3:

$ time windows_terminal_issue
Terminal in raw mode - 'q' to exit early
it should end on its own otherwise after 100000
[99999] Read 7 bytes: "\x1b[5;41R"
Done
Terminal restored to original , err <nil>

real    0m1.746s
user    0m0.132s
sys     0m0.378s

latest:

$ time windows_terminal_issue
Terminal in raw mode - 'q' to exit early
it should end on its own otherwise after 100000
[99999] Read 8 bytes: "\x1b[48;42R"
Done
Terminal restored to original , err <nil>

real    0m2.557s
user    0m0.151s
sys     0m0.455s

Ghostty Logs

No response

Ghostty Version

Ghostty 1.2.1-main+dafb9e89a

Version
  - version: 1.2.1-main+dafb9e89a
  - channel: tip
Build Config
  - Zig version   : 0.15.1
  - build mode    : .ReleaseFast
  - app runtime   : .none
  - font engine   : .coretext
  - renderer      : renderer.generic.Renderer(renderer.Metal)
  - libxev        : kqueue

OS Version Information

26.0.1 (25A362)

(Linux only) Display Server

None

(Linux only) Desktop Environment/Window Manager

No response

Minimal Ghostty Configuration

empty conf also has the issue though it is worse with

background-opacity = 0.7
background-blur = 10

### Additional Relevant Configuration

_No response_

### I acknowledge that:

- [X] I have reviewed the FAQ and confirm that my issue is NOT among them.
- [X] I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
- [X] I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (` ``` `) on separate lines.

[ldemailly]

I updated the code to add timing over time in the hope of reproducing the slow down over time part of the issue but that doesn't reproduce it, only fps does so far - on the other hand I discovered that running the simple repro, just after running fps is significantly slower - and I am not sure why (some residual mode change? pixels on screen?) - and only with latest ghostty - the timing shown in 1.1.3 do not change whether fps was run before it or not:

while latest/tip :

same latest process but from a new window:

for ref, current versions:

# repro with intermediate timing
go install github.com/ldemailly/go-scratch/[email protected]
# fps
go install fortio.org/terminal/[email protected]

[franksl]

I can confirm a similar behavior on my Ubuntu 24 machine, using i3 window manager and tmux.
I experience the terminal response getting slower and slower over time, with cpu usage by the ghostty process going over 10-15% at idle.
Simply typing characters is very fast at first, then it becomes visually slower over time.
If I detach from the tmux session, close ghostty, then re-open ghostty and reattach to the tmux session (or use another terminal software), the speed returns back to fast for some time, so I'm pretty sure tmux is not the culprit.