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Comment by zeendo | Hacker News Reader

I have perf issues with emacs-pgtk on a 4k screen on Wayland with Niri in both Emacs as a client and not. The issues appear with typing or scolling, the delay and lag become noticeable.

For me the issue is only unbearable when running fractional scaling, for some reason.

I'm going to try the branch mentioned in the sibling comment, though.

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I have almost the exact same setup as you and even have strange behavior with fractional scrolling. I'm on NixOS so the setup is even inspectable: https://codeberg.org/arik/dotfiles

After resetting the scale from 1.2 to 1.0 through 'niri msg output HDMI-A-2 scale 1' I actually noticed a performance increase! I will have to troubleshoot this, although you may have stumbled on a great lead toward the root cause.

Also on Niri with fractional scaling and pgtk. IIRC the issue here is that for programs that don't support wp_fractional_scale, compositors deal with this by rendering at the next highest integer factor, and downscaling it down to achieve the desired factor. This is much, much worse for Emacs since it uses GTK3 and doesn't support hardware acceleration with Cairo, at least according to Po Lu [1] so you're effectively rendering via CPU at a very high resolution.

For XWayland apps Niri just renders at the native resolution (ignoring scaling), meaning a decent workaround is to use the Lucid/non-pgtk version and manually scaling up the UI. Unfortunately I go from scaling at 1.25 on my screen to 1.00 on my external monitors, which means I can't use the non-Wayland versions without messing up the font size on either my desktop and monitor.

[1] https://mail.gnu.org/archive/html/bug-gnu-emacs/2024-09/msg0...

I'm also on Emacs and Niri, seems to be a popular combo, and I don't have any performance problem.

At home I'm driving an Ultrawide (3440x1440@75Hz) at scale 1.1.

At work I'm driving two 4k screens at scale 1.2.

I might be less sensitive to latency but it could also be a graphics driver issue or something similar. I'm using Arch with emacs-wayland (pgtk) with a strix halo (all AMD) laptop.

It might also just be the case that the hardware you have is good enough that the lag isn't noticable.

You should still be able to notice a spike in CPU usage whenever you force Emacs to redraw the frame by typing into it though.

I didn't invent this mitigation FWIW - I saw it mentioned in one or another thread about this by someone else - possibly on the big reddit thread on this topic, not sure.

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