Support for hibernation 2/2: questions

[Chris Murphy]

Continued from the 'background and summary' email:
https://lists.fedoraproject.org/archives/list/[e-mail]...

Adding Hans and Matthew and Lennart to cc.

Questions I have are:

- WG is considering dropping creation of swap partitions by default,
in favor of swap-on-ZRAM. Any concerns? (We do know it's not possible
to use a ZRAM device for hibernation, but the kernel will look to
another swap device for contiguous free space to write out a
hibernation image.)

- What's the status of s2idle in the kernel?

- What sort of work is needed outside the kernel to properly support
s2idle, or is this predominantly kernel work? Microsoft documents on
Modern Standby suggest minimal application effort. [1]

- Prospect of kernel support to separate swap and hibernation
partitions (and/or swap files)? Or systemd method of creating then
activating swapfiles on demand?

- Prospect of hibernation supported with UEFI Secure Boot?

- Is hibernation a better fallback than poweroff, given the
significant reliability differential? Why? Poweroff is universal,
hibernation isn't. What's the argument that a non-universally
available fallback is better than the universal fallback?

- What are the implications of hibernation if Fedora will move to
measured boot? (I'm not sure how mainstream that function is expected
to be, or it's use case specific opt-in.)

- There's some anecdotal evidence users are disabling UEFI Secure
Boot, possibly quite a lot [2]. Does there need to be an effort at
making the signing of user built kernel and module easier? Can it be
made easier? I don't know custom or out of tree modules is a
significant motive for disabling SB, vs other explanations.

- A systemd TODO makes me wonder: Does anyone have (corroborating)
data on the reliability of firmware or battery reporting, when the
system, and thus the battery, are under significant load? [3] I've
discussed with a reliable source that on 2+ year old hardware, the
vast majority of batteries are effectively broken and aren't likely to
report anything reliably if they are under significant load, in
particular waking from S3. By anything, I mean, time remaining, power
remaining, and current power consumption rate. Would s2idle instead of
S3 would make this more reliable?

- It doesn't sound like S1 is really used at all, even though kernel
docs say it's supported as shallow/standby. (?) Is it more or less
reliable than S3?

- I'm inclined to think we should mimic what hardware vendors,
Microsoft, Apple, and Google (with Chromebooks and Android) have been
doing for a while: faster boots, and S0 low power idle - and skip the
things making devs and users crazy. But I invite a persuasive contrary
argument.

- Any other questions?



[1]
https://docs.microsoft.com/en-us/windows-hardware/design/device-experienc...
[2]
https://twitter.com/hughsient/status/1225826488903249920
[3] see line "beef up hibernation"
https://github.com/systemd/systemd/blob/master/TODO
-- 
Chris Murphy