1047355 - Improve USS reporting in WebIDE Monitor

Status: RESOLVED FIXED

(DevTools Graveyard :: WebIDE, defect)

Description

[Jan Keromnes [:janx]]

Currently, USS reporting in the Monitor has the following issues:

- Doesn't work if the FxOS runtime is older than 2.1.
- Tracking certified apps requires the `devtools.debugger.forbid-certified-apps` pref to be `false`.
- Tracking requires the (currently) heavy memory+processing footprint of devtools actors inside every process.
- The data coming back is irregular, because every process is polling its memory independently.

All these issues can be addressed if we change the reporting mechanism to parse the output of `b2g-info` instead of relying on the monitor actor to poll each process.

Parsing `b2g-info` output is not ideal and it's a hack, so any parsing should be replaced by bug 1043324's reporter as soon as possible (this will take time though because several non-trivial bugs need to be fixed first).

Comment 1

[Jan Keromnes [:janx]]

Attachment: Poll b2g-info for USS (does it work on user builds?).

Comment 2

[Jan Keromnes [:janx]]

WIP, obviously.

Comment 3

[Jan Keromnes [:janx]]

Attachment: Reduce USSAgent polling frequency.

This reduces the perf hit of USSAgent a bit.

Comment 4

[Jan Keromnes [:janx]]

Attachment: Poll b2g-info for USS when possible.

When possible, parse the output of `b2g-info` to get the USS and ignore updates
from multi-process USSAgents (inside the Monitor actors of each b2g process).

The USSAgent updates are still received (albeit at slower frequency and only for
non-certified apps if the pref is absent) so when `b2g-info` is not available or
doesn't work (e.g. on the simulator), we gracefully degrade to USSAgent updates.

The b2g-info trick has several advantages:
1. Works for older Firefox OS devices (pre-2.1).
2. Doesn't need certified-apps debugging.
3. Polling time is synchronized for all processes.

And some drawbacks:
1. Parsing output from ADB shell is a hack.
2. Doesn't when debugging over Wi-Fi.
3. ADB needs to be root for `b2g-info` to work.

Paul, regarding drawback 3, does the ADB helper try to become root when possible?
Is there a way I can request ADB to be root before polling b2g-info?

Comment 5

[Alexandre Poirot [:ochameau]]

(In reply to Jan Keromnes [:janx] from comment #4)
> And some drawbacks:
> 1. Parsing output from ADB shell is a hack.
> 2. Doesn't when debugging over Wi-Fi.
> 3. ADB needs to be root for `b2g-info` to work.

All the recent tricks to use adb helper to run adb commands are hacks.
We should use that we great care.

Comment 6

[Jan Keromnes [:janx]]

Blocked on bug 1048024 because b2g-info is broken.

My patch still works tough:
- Using a device with broken b2g-info (trunk fxos), USS properly falls back to actor updates.
- Using a device with working b2g-info (older fxos), USS actor updates are properly ignored and b2g-info is used instead.

(In reply to Alexandre Poirot [:ochameau] from comment #5)
> All the recent tricks to use adb helper to run adb commands are hacks.
> We should use that we great care.

I agree. That's why I try to be very careful in my code, and fall back to actor updates as soon as anything looks suspicious.

Comment 7

[Paul Rouget [:paul]]

(In reply to Jan Keromnes [:janx] from comment #4)
> 3. ADB needs to be root for `b2g-info` to work.
> 
> Paul, regarding drawback 3, does the ADB helper try to become root when
> possible?
> Is there a way I can request ADB to be root before polling b2g-info?

http://mxr.mozilla.org/mozilla-central/source/browser/devtools/webide/content/runtimedetails.js#89

Comment 8

[Paul Rouget [:paul]]

Could we have a test on the phone that would break if b2g-info output can't be parsed the way it is parsed in monitor.js?

Comment 9

[Jan Keromnes [:janx]]

Checkin needed of the b2g-info polling for now.

We might want to reduce USSAgent polling frequency eventually.

Try: https://tbpl.mozilla.org/?tree=Try&rev=75743abfcbdd

Comment 10

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/integration/fx-team/rev/a3c0beca4898

Comment 11

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/a3c0beca4898

Comment 12

[Jan Keromnes [:janx]]

Actually, let's see about the USSAgent polling frequency in another bug if needed.