Version 2.7b2, the second public beta release of App Tamer 2.7, is available on the App Tamer Beta Testing page. If you’ve recently downloaded beta 1, just choose “Check for Update” from its utility menu or in the Options tab of App Tamer’s Preferences window to get the new version.

The changes in beta 2 are relatively small, correcting interactions between the new capability of running apps on the M1 processor’s efficiency cores and several existing App Tamer options. In addition, App Tamer’s online help has been brought up to date, and a bug affecting the CPU usage graphs in beta 1 has been fixed. Details and download links are available on the beta testing page.

If you have any feedback or bugs to report on the 2.7 beta releases, please share them in the comments here or by emailing AppTamer@stclairsoft.com. Version 2.7 is on track for release soon, barring any further bug reports or changes.

There’s now a public beta version of App Tamer 2.7 available for download. The big deal in this iteration is support for the Performance and Efficiency cores (or “P and E cores” for short) in Apple’s M-series processors.

P and E core usage statistics

As you can see in the image on the left, App Tamer now displays graphs of P and E core usage as well as overall CPU usage. You’ll get these automatically if you’re running App Tamer on an M1-powered Mac.

Note that P and E stats are shown as a proportion of total CPU power available, so on an M1 Pro processor (8 P cores and 2 E cores), the E core number will max out at 20% (2 cores out of the 10 available), while the P core number will max out at 80%. This may be a little counter-intuitive at first, but it was even more confusing to represent them as a percentage of each core type. In that scenario, “CPU Used by All Apps” could show 50%, with E core usage at 100% and P core usage at 38% – which doesn’t make sense to most normal humans.

Running background apps on E cores

This is the really cool part. When you click on an app in the process list to change its settings, there’s an additional “Run this app on the CPU’s efficiency cores” checkbox, as you can see in the screenshot below.

I explained the basics of this feature in a previous post. It works like App Tamer’s other CPU-saving capabilities in that it’s applied to an app anytime that app is not frontmost. If you turn on the checkbox for Safari, any time that you leave Safari running in the background while you’re using another app, Safari will be switched to the processor’s E cores. This saves power and leaves the P cores free to handle higher priority tasks.

Note that the effects of this feature are similar to App Tamer’s existing “CPU throttling” capability, which is what you get when you turn on the “Slow down this app if it uses more than X%” checkbox. However, there are a couple of advantages:

• The E cores actually consume less power by design
• There’s no overhead when running an app on E cores, whereas throttling an app’s CPU usage requires App Tamer to actively manage the app’s execution

So, basically, running an app on the processor’s E cores saves more power than throttling it.

Of course, the two aren’t mutually exclusive – you can run an app on the CPU’s E cores and throttle it while it’s there if it’s still using too much processing power. App Tamer will let you turn on both checkboxes to do this.

What about Intel-powered Macs?

If you’re not using a fancy new M1 or M2 (soon?) powered Mac, you won’t get this new feature. However, that checkbox does still do something. It’s named “Run this app as a low-priority process” on Intel Macs, and it will use the macOS system scheduler to reduce the priority of the app, both in terms of CPU usage and disk and network I/O. This will reduce its impact on other apps and cut its energy usage somewhat, but not nearly as much as it does on M-series Macs.

OK already! Where do I download it?

Go to the App Tamer beta testing page. And if you have suggestions, find a bug, or want to argue with me about how E and P core usage is displayed, send email to AppTamer@stclairsoft.com.

So I was reading Howard Oakley’s Eclectic Light Company blog, as I often do (and you should too), and he mentioned the taskpolicy command line app, which I wasn’t aware of before. taskpolicy allows you to demote a process to “background priority,” making it run more slowly by giving it a lower priority for its disk and network access and – key point here – on M1-powered Macs, also runs the process on the M1’s efficiency cores instead of on the performance cores.

That got me thinking… if there’s a command line tool to do this, there must be a system API to make this happen, too. And lo and behold, the setpriority( ) system call will actually perform this neat trick, even though the man page lies and says it won’t.

I made some changes to App Tamer yesterday to add this, and App Tamer now has a new checkbox:

Turn the checkbox on, and whenever an app isn’t frontmost, App Tamer will give that app background priority, reducing its disk and network priority and switching it over to run on an M1 efficiency core. Running a few apps that consume quite a bit of CPU looks like this in Activity Monitor:

In my initial testing, the feature seems to work quite nicely. App Tamer automatically moves apps between the performance and efficiency cores as you switch between apps. So far, I haven’t found any downsides to this – but then again, I just added the feature yesterday and have only done limited testing. It’d be great to actually quantify whether this delivers additional battery life.

If you’d like to give it a try, you can download App Tamer 2.7d1 here. Just unzip it and run it, then click on a cpu-hungry app in App Tamer’s process list and turn on “Run this app on an M1 efficiency core” – that’s it. App Tamer will automatically lower the app’s priority when it isn’t frontmost.

Update: There’s now a beta version of App Tamer 2.7 that includes an almost-finished version of this feature.

Note for users of Intel-based Macs: On your machine, the checkbox is named “Run this app as a low-priority process” because your Mac doesn’t have separate efficiency and performance cores 😢. The app will be demoted to background priority so it uses fewer CPU and I/O resources, but I’m afraid there’s no fancy cpu-juggling involved.