Load Visualizer

Flames from the bottom show user load. Clouds descending from the top show system load. The most loaded cores show in the middle.

So if the flames are high in the middle it means that one / a few cores are maxed out. If the flames are sort of high everywhere it means that all cores are working.

And if you have lots of system load, it can mean that you're short on RAM / swapping.

This provides you with a visualization of the current system load, covering CPU usage and RAM pressure.

System and User CPU load are measured for each logical core of the system. RAM pressure has to be inferred:

• If the user part is high on one CPU, getting CPUs with better single core performance might help.

• If the user part is high on lots of CPUs, getting more cores might help.

• If the system part of the CPU load is high, this can mean that your system is swapping, and that getting more RAM might help.

Installation

Easiest way is by using Homebrew:

• In a terminal: brew install walles/johan/loadviz && open /Applications
• Right click LoadViz in the new Finder window to open it

Parts

There's one macOS app done in Swift and one library done in Rust.

Why not measure RAM / swap usage?

People commonly think measuring RAM / swap usage will help them decide...

• When to close apps / tabs
• When to buy more RAM
• When to get faster swap

... but the truth is it won't help with any of that. Conclusions drawn from those numbers will generally be wrong, and presenting them would just be confusing.

Swapping out unused memory

Let's say you have 8GB RAM, but you're using 25GB. 6GB is resident, 19GB is swapped out and 2GB RAM is "free" / used as disk cache. Also, let's say that only 4GB of RAM is actually needed right now, and the other 21GB just happen to be around but are not going to be used during the near future.

Any RAM / Swap visualization would show this as critical because you're silly high over quota.

But in reality, since you aren't using most of the memory, this is fine.

Cost of swapping

Let's say you have two computers, both doing the same thing and having too little RAM.

One of them is swapping to a (slow) hard drive, and one to a (fast) SSD.

Then, even with the exact same memory numbers, the SSD machine will be in a lot better situation than the HD machine.

How would you visualize this?

TODO

• Animation sometimes looks choppy on macOS, ensure that we actually do 10FPS
• On macOS, ensure that we actually auto start on login. Seems like it used to work but doesn't any more in newer LoadViz versions.
• Overlay the screenshot animation on top of an actual screenshot from macOS
• Make a Touch Bar visualization
• Poll battery charge state as well
• Visualize battery charge as a blue sky (full) or a starry night (empty)
• Make a Dock icon visualization

Done

• Make the library export some C API that gets called by the Swift app
• Make the library return an image, any image
• Make a macOS app rendering this image in a window
• Make the demo app not just show black all the time even though the image from Rust is red
• Make demo binary update its image at 3 FPS
• Add cargo build of our library to the Xcode project's build process
• Make demo binary update its image at 10 FPS
• Draw some sort of bar chart
• Base bar chart on fake data for one CPU
• Make sure that data looks like CPU load (user / system / idle) and that the bars are based on that
• Make sure we can render everything from one CPU to more CPUs than the width of the display
• Make the bars look like sound visualizations
• Add test making sure mirror_sort() doesn't fail when two values are equal
• Replace the data with actual CPU load
• Test that we can render a zero-length CPU-loads array without crashing
• Make bars slide into place when metrics are updated
• Add micro benchmarks for the rendering code
• Profile the micro benchmarks and make the code faster
• Make a desktop app
• Make the desktop app show a menu bar icon
• Update the menu bar icon at 10Hz with the system load
• Don't hard code the dimensions in LoadVizView
• Make clicking the menu bar icon bring up a menu
• Add a "Quit" menu item
• Hide the desktop app icon from the Dock
• Hide the desktop app from cmd-tab
• Profile our release build to see if we can make it faster
• Make the desktop app start automatically on login: https://jogendra.dev/implementing-launch-at-login-feature-in-macos-apps
• Make sure our auto launcher doesn't pollute the global namespace
• Make sure the visualization doesn't start out as all-black
• Replace the whole visualization with red user flames from the bottom and green system flames from the top
• Test that diff() handles wrapping CPU counters correctly
• Get Git metadata into the release archive
• Add an "About" menu item doing something helpful. At least link to the GitHub project and show some version number.
• Run (a release build!) by default on Johan's desktop
• Add a Help menu item explaining how to read the visualization
• Make sure the visualization doesn't go to 100% after showing the About dialog
• Make sure we can install a packaged LoadViz on some other machine
• Add a license
• Release the first public version on GitHub
• Package using HomeBrew
• Stop using CPU when the menu bar isn't visible
• Draw system load as a cloud rather than an upside down fire
• Anti-alias cloud horizontally to avoid sharp vertical edges
• Add a screenshot to the top of the README.md file, close to the explanation of how to read the display
• Make the cloud outline look cloudier
• Make the clouds look more realistic:
  • Have less details in the clouds
  • Animate the clouds slower
• Improve idle-system performance by only trying to render clouds where they could be, and the same thing for the flames.
• Figure out whether cargo build should be done in the libloadviz project instead. Well, it shouldn't. No problems related to this seen in a long time.
• Make the macOS About dialog show the latest macos- version number rather than a date
• Make sure the icon is visible in the About dialog
• Make sure the icon is visible in the Finder
• Make an icon
• Make icon follow Apple's HIG: https://developer.apple.com/design/human-interface-guidelines/app-icons
  • We didn't really, but at least we matched our size and corner radius with the Safari icon's size / corner radius.
• Make Activity Monitor show "LoadViz" as a name, now it's empty
• Animate the screenshot in a cross faded loop
• The fire in the icon has some weird corner-like artifact, also visible in the screenshot, make that go away