835681 - Remove the sync messages from BrowserElementChild startup

Status: NEW

(Core :: DOM: Core & HTML, defect, P3)

Description

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Looking at

http://people.mozilla.com/~bgirard/cleopatra/#report=427594015c91a5fedfa918262af7c4767efa68c5

the sync messages in _init() are consuming a lot of the profile.  By my analysis so far, I don't think they're real overhead, but they're very distracting and in a different factoring of the startup code, they could become real overhead.

Comment 1

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Attachment: PoC

Not a serious patch, just for testing purposes.

With these changes, the stopwatch timing of startup doesn't seem to change (at least I can't measure a difference) which is expected, but we do have happy times: an idle event loop during early startup waiting for OnInputStreamReady()!

Comment 2

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Aha!  The idle event loop is actually an async-sync wait on the b2g process, to return an fd for the application.zip.

So if we pre-open() and send over the application.zip fd, we'll actually reduce real work and should see a win.

Comment 3

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

(I know you're occupied with other work, but) do you have a proposal for how to avoid these messages?

Comment 4

[Justin Lebar (not reading bugmail)]

I was thinking we'd just send a blob of properties when the child starts up.  A simple hack would be to set some properties somewhere and then just read them out later.  Perhaps we could use prefs for this (using the knowledge that they won't be forwarded up to the parent)?  Otherwise it's simple to add a service.

Comment 5

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

frame scripts can ask nsITabChild for things, in a not too terribly gross way (IIRC).

Comment 6

[Julien Wajsberg [:julienw]]

bug 835698 comment 54 implies we should eventually fix this here for a nice startup perf boost. So asking for at least tracking here.