Suspend/Resume

Posted May 5, 2017 22:39 UTC (Fri) by fratti (guest, #105722)
In reply to: "AnalyzeBoot" by johnjingleheimer
Parent article: 4.12 Merge window part 1

>https://01.org/suspendresume

Huh, isn't the normal thing for "fast" power-saving to set the processor into lower p-states? I mostly know suspend/resume from laptops, since for phones you'll still want to occasionally do things in the background, and for servers you're really just waiting for a new request of some form to come in, or a batch job to start.

Is this some work to make suspend/resume fast enough so it can be initiated automatically without possibly annoying the user?

Suspend/Resume

Posted May 6, 2017 9:29 UTC (Sat) by flussence (guest, #85566) [Link] (3 responses)

The automatic suspend/resume feature already exists in the kernel under CONFIG_PM_AUTOSLEEP. It's nearly useless on an average x86 ACPI machine; ARM platforms can enter/leave the equivalent of S1/S3 state in milliseconds, so it's the main method of power saving there. Compare the responsiveness of the "power" button on a phone to the suspend button on a laptop - they do the same thing.

It sounds like Intel is making a serious attempt to catch up on that front, and if they can get a high wattage Xeon to wake on LAN and start servicing requests in under a second I can see it becoming a big selling point. They need to get there before ARM servers start eating their lunch en-masse, though.

Suspend/Resume

Posted May 6, 2017 15:01 UTC (Sat) by fratti (guest, #105722) [Link] (2 responses)

Ah, I did not realise phones entered such a deep sleep when the screen was locked. I always figured if that was the case, the wireless connections and such would drop, but I guess these are handled by external chips and they can wake up the main processor when something interesting is happening.

Thanks for the insight on this!

Suspend/Resume

Posted May 12, 2017 9:55 UTC (Fri) by oldtomas (guest, #72579) [Link]

> but I guess these are handled by external chips

Well, kind of, only that they are subsystems (with CPU, RAM, ROM)... on the same chip. Cost pressure has forced maufacturers to move next to everything into That One Big Chip.

Although unrelated, those two articles have the nice collateral effect to update one's idea of the current State of the Phone:

https://googleprojectzero.blogspot.de/2017/04/over-air-ex...
https://googleprojectzero.blogspot.de/2017/04/over-air-ex...

(and, btw, it's through LWN that I was made aware of them).

Suspend/Resume

Posted May 16, 2017 15:42 UTC (Tue) by flussence (guest, #85566) [Link]

Wi-Fi standards are a twisty maze of layered hacks to facilitate power saving. Chances are your phone is mostly disconnected when it's switched off, but reconnects fast enough when it wakes up to put on a convincing illusion that it's always-on.

Most Android phones also have Play Services and its server-push API, so instead of O(n) apps polling for new messages separately it's a single connection to Google's servers. (Anecdotally, I found my phone's battery life tripled after removing the Google-ware, but that's probably more to do with it triggering the OOM killer constantly...)