Comment by cruffle_duffle
2 days ago
That is so weird. How much mAh can a single “wake and renew lease” possibly take? Like it has to be milliamp-milliseconds (mAmS?). I mean my phone is chattering with the cell network probably all the time even in a fairly deep sleep mode. The laptop is lighting up the WiFi stack to send and receive (and process) like a few packets?
Like you said though, it’s pre Apple silicon so who really knows! Maybe it decided to do some other stuff while it was awake?
Your cell phone modem is completely decoupled from the main processor and is a complete, independent system in itself, so it's optimized to do that.
Bluetooth and WiFi radios on Macs are also semi-independent. They can keep connections alive while the system is in deep sleep.
Waking a big processor, frequency scaling it and turning it off is surprisingly complicated. We disabled SpeedStep in our clusters since frequency scaling visibly affected performance of the systems due to overhead incurred by frequency change. Same is true for waking / sleeping big silicon.
It's complicated, it's wasteful.
Some of the Intel's biggest improvements as their micro-architecture evolved were reduction of the frequency scaling overhead and its performance impact, but this never made the news back in the day because its effect was invisible in consumer class systems even in its most primitive form.
> Maybe it decided to do some other stuff while it was awake?
That's called Power Nap and is enabled only if your computer is connected to power, by default.
It may stay on longer than the amount of time it takes to renew. Perhaps for every wake it stays on for 60 seconds; it is also doing other things like checking mail.
I wonder if some user-space process lights up and throws a wrench in things.
I’m sure both Microsoft and Apple have entire teams with incredibly full backlogs dealing with power management. And I’m sure half their time is spent dealing with “messes” caused by other teams doing wild and crazy (but somehow theoretically useful) shit.
It’s clearly not an easy problem.