My recommendation is to make this RBS until this is fully triaged. There is risk of corruption/data loss.

bhthompson@ do you have any owner in mind for this issue?

derat, is this something in your jurisdiction?

dspaid, or is this something you would be able to help with?

Either way this is not a regression, we did migrations in 60 without this, and this should not block 61.

This was discussed at length during the design of the migration process.

https://docs.google.com/document/d/1-8hcSyTbnFh_Kzat4x2-K7J9zcg8JUG9rjTPBTtlVMY/edit#heading=h.nfkk2fmjp5xi
https://docs.google.com/document/d/1csXazWS9UvZ4fdWN2jz_kbDKnF_cdOdPYrheemtijv8/edit#heading=h.hpn72ii2h7qu
etc.

The claim at the time was that there is no risk of data loss due to power loss.

If you're just concerned about keeping the screen on, there are plenty of ways for Chrome to request that already. See device::PowerSaveBlocker with kPowerSaveBlockPreventDisplaySleep, for instance.

Correct, there should be no risk of data loss due to power loss.  We do still try to avoid mid-migration shutdown because its not feasible to test all corner cases and it provides a worse user experience.

Back to the main topic though, I don't think keeping the screen on was ever discussed.  I have no strong opinions one way or the other and will defer to PM/UX as to what the behavior should be.  The actual logic to prevent screen-off should be pretty simple.  We already have an "encryption_migration_active_" flag in PowerPolicyController to prevent shutdown on lid close, so it should just be a matter of also overriding the screen_off_ms fields.

https://cs.chromium.org/chromium/src/chromeos/dbus/power_policy_controller.cc?dr=CSs&l=379

So, it's not an issue of data loss, but it is more of how much do you expect your migration to happen. 
If it goes to sleep after 7 minutes and is waiting for user operation to resume from sleep, that's bad.

Are we saying that the display goes off or are we saying that the machine goes to sleep?

The display goes off, the machine stays awake and finishes the migration.  The concern in the initial report is just that it could be confusing to the user (they see the screen go off and assumed that the migration finished and rebooted).

The intended behavior during migration is:
- Prevent the system from sleeping
- Do not prevent the display from going to sleep

Did the system go sleep? If so, it sounds a regression.

did we come to a conclusion?

We don't have a conclusion.

The device won't sleep during migration.
Only the screen will be turned. It is expected under the current implementation.
IIUC, the suggestion in #1 is that keeping the screen on during migration should avoid user's confusion.

I don't have a strong opinions on this.
Can someone from PM/UX take this issue and decide the expected behavior?

My personal opinion is that we should keep the display on, but I'll check on who the right PM/UX owner for this should be.

+shihuis@ - Could you take a look and advise?

If we wait long enough, the problem will take care of itself due to all users having already gone through the migration. :-P

Long enough meaning months until we forcibly migrate users? ;) 

Let's keep the screen on during migration. This will ease user worry of what is happening by always showing the screen and progress. There will also be no misunderstanding of turning off vs screen falling asleep. 

Let's fill in some background information so that shihuis can make an informed decision:

we're tralking about display going dark after a while; 
current 95%tile time to migrate is around 15 minutes.
For those kind of users after 8 minutes screen goes blank but migration keeps on happening. After 8 more minutes the machine will reboot. Do we need to keep the screen on?
(I guess maybe yes).

possible argument against turning on the screen would be wasting battery.

Thanks Junichi for the background.

The use case I'm particularly worried about is users looking at their chromebooks and seeing that it's black, so thinking that the migration is done. 

The battery draining is a possible issue but given that the data is safe, always leaving the screen on should be more instructive.