Reference
Performance
How much CPU and memory mielwm uses, and how to check it on your own Mac.
At rest
Most of the time mielwm does nothing at all. There are no timers polling and nothing redrawing in the background, so between your actions it sits at about 0.01% of one CPU core. Memory starts around 50 MB and settles near 145 MB once you've opened the overview, because it keeps a small still of each window. You won't find it in Activity Monitor's top list unless you go looking.
Switching workspaces or moving a window costs a short spike, about 1% of a core for the moment the windows move, then it drops back to rest.
In the overview
The overview is the part that does real work. It shows a live picture of every window, so its cost depends on how much those windows change.
| While the overview is open | CPU | Memory |
|---|---|---|
| Windows sitting still | about 1% | about 225 MB |
| Every window playing video | about 10% | about 355 MB |
Most windows sit still most of the time, so the first row is what you'll see day to day. A window that doesn't change costs almost nothing to show, and when nothing on screen changes the overview stops redrawing until something does. One playing video updates up to 60 times a second, and that's where the CPU goes.
When you close the overview, the live pictures turn into small stills. mielwm keeps those so the overview opens with pictures right away next time. Within a minute it's back to about 0.01% CPU and about 145 MB, and the stills of windows you haven't seen for a few minutes shrink further.
With AeroSpace-compatible apps
A menu bar app pointed at mielwm, as AeroSpace-compatible apps describes, asks for your workspaces on a timer. How often depends on the app.
An app that asks every 5 seconds costs nothing you'd notice. One that updates ten times a second runs the aerospace command about 40 times a second, since each update takes several calls. Each call costs about 4 ms of CPU, so at that pace it adds up to about a seventh of a CPU core, plus whatever the app spends on its side. If that matters to you, pick an app or a version that asks less often.
Check it yourself
Open Activity Monitor, search for mielwm, and watch the CPU and Memory columns while you work. Memory is the physical footprint, so it grows with the number of windows the overview has pictures of.
The numbers on this page come from an M3 Pro on macOS 27, with 8 windows managed. Runs with playing video move by about 2 points from one try to the next. mielwm's repository has a benchmark script that measures all of this on a test copy, away from your own windows. CONTRIBUTING.md explains how to run it.