NEPacketTunnelProvider causes very high energy impact in main app

It sounds like you are on the right track here by using Instruments to narrow down where this impacts are being incurred in your app. Based on what you mention it sounds the container app is causing these issues, so I would start profiling your container app using Allocations or Timer Profiler templates on the container app. The Allocations template allows you to take a look at a trace of your app from a thread by thread basis to see where on each thread your container app may be spending time. This would then allow you to tweak parts of your code and re-run the trace.

Matt Eaton
DTS Engineering, CoreOS
meaton3@apple.com

Hi @meaton, I have indeed taken a look at the Allocations and Time Profiler instruments. Neither of them yield anything out of the ordinary. CPU usage and allocations look fine — pretty much completely idle when the app isn't being interacted with in fact. Despite that, the energy impact and network/overheads in Xcode are still showing very high, but only when the packet tunnel is running.

I commented out all of the code for the inter-process requests so there are no timers running or sendProviderMessage calls being made, the container app makes no network requests whatsoever and yet the problem still occurs.

If the problem is in my own code, I can't see where it is. I am wondering whether iOS is continuously sending counters/statistics/events or something from the packet tunnel back to the container app or something similar? You can probably guess from the graph for the container app when I started the VPN:

Meanwhile, the Energy Impact of the actual VPN extension process itself:

Squarely out of ideas so any thoughts appreciated!

I commented out all of the code for the inter-process requests so there are no timers running or sendProviderMessage calls being made, the container app makes no network requests whatsoever and yet the problem still occurs.

Great, thank you for ruling this out of the equation.

Regarding:

I am wondering whether iOS is continuously sending counters/statistics/events or something from the packet tunnel back to the container app or something similar?

There could be NEVPNStatus events being sent to the container app, but I am doubting it would could cause network overhead in your app. Are you observing events for NEVPNStatusDidChangeNotification?

Matt Eaton
DTS Engineering, CoreOS
meaton3@apple.com

There could be NEVPNStatus events being sent to the container app, but I am doubting it would could cause network overhead in your app. Are you observing events for NEVPNStatusDidChangeNotification?

Thanks for the tip. I do indeed subscribe to NEVPNStatusDidChange, although that only fires a couple of times (when the VPN changes state, as expected). I commented that out too so that we're no longer observing that, for good measure, but the problem still persists.

I commented that out too so that we're no longer observing that, for good measure, but the problem still persists.

Okay, thanks for the confirmation here. If you run out of options and are stuck on this, feel free to open a TSI and I can try and take a closer look at what might be happening. Please make sure to include a focused sample so that I can try and reproduce this on my end.

Matt Eaton
DTS Engineering, CoreOS
meaton3@apple.com