1149612 - Improve nsHttpChannel::AsyncOpen() performance

Status: NEW

(Core :: Networking: HTTP, defect, P3)

Description

[James Willcox (:snorp) ([e-mail]) (he/him)]

Attachment: Profile. Look at 2751ms to see where we start preloading.

We spend a pretty decent amount of time just firing off network requests, which is clogging up the main loop. In the attached profile, we fire off a couple dozen speculatively requests for images, and it takes us nearly 200ms (2751ms - 2939ms). It seems like this could be better.

Comment 1

[James Willcox (:snorp) ([e-mail]) (he/him)]

Some of this is figuring out UA overrides, which I disabled in the attached trace. Bug 1148544 was filed for that specific issue, and contains a profile with the callbacks enabled.

Comment 2

[James Willcox (:snorp) ([e-mail]) (he/him)]

10% of the time is in mozilla::net::PredictorLearn(). It seems like that could be moved off the main thread if it has to do actual work.

Comment 3

[James Willcox (:snorp) ([e-mail]) (he/him)]

Looks like a substantial amount of time spent in nsChannelClassifier::Start(). Of that, I sometimes see nsThread::PutEvent() showing up.

Comment 4

[James Willcox (:snorp) ([e-mail]) (he/him)]

I think OpenCacheEntry() might be the biggest offender here (other than comment #1).

Comment 5

[Honza Bambas (:mayhemer)]

(In reply to James Willcox (:snorp) ([e-mail]) from comment #4)
> I think OpenCacheEntry() might be the biggest offender here (other than
> comment #1).

Can you get more granularity here?

Comment 6

[James Willcox (:snorp) ([e-mail]) (he/him)]

(In reply to Honza Bambas (:mayhemer) from comment #5)
> (In reply to James Willcox (:snorp) ([e-mail]) from comment #4)
> > I think OpenCacheEntry() might be the biggest offender here (other than
> > comment #1).
> 
> Can you get more granularity here?

I can try, yeah.

Comment 7

[Firefox Bug Husbandry Bot]

Bulk change to priority: https://bugzilla.mozilla.org/show_bug.cgi?id=1399258

Comment 8

[Firefox Bug Husbandry Bot]

Bulk change to priority: https://bugzilla.mozilla.org/show_bug.cgi?id=1399258