Junior - is this something you could investigate?

(In reply to Selena Deckelmann :selenamarie :selena use ni? pronoun: she from comment #9)

Junior - is this something you could investigate?

Given Comment 4 and Comment 6, IMO it could be a P3 for now. It could be my backlog but I'm not familiar with the pb-Http setup.

QF triage team has reviewed this bug and it seems like a pageload issue.

I think moving decompression off the main thread would help quite a bit.
Here's a more recent profile with 175ms spent inside nsHTTPCompressConv::OnDataAvailable: http://bit.ly/2ShNR8P
This is from loading https://www.facebook.com/DwayneJohnson .

Generally, the main thread is always busy during page load; the more work we can move off of it, the better. And things that are already asynchronous from the main thread's perspective (such as network requests) are a particularly attractive target.

Hi :dragana,

What all is required to accomplish this? Is it sufficient to read the data from the HTTP stream into a buffer and then pass that off to a thread to do the decoding?

(In reply to Barret Rennie [:brennie] from comment #13)

Hi :dragana,

What all is required to accomplish this? Is it sufficient to read the data from the HTTP stream into a buffer and then pass that off to a thread to do the decoding?

we have away to deliver onDataAvailable off-mail-thread, but all listeners must agree.
For listeners that require onDataAvailable to be deliver on the main thread but are encoded to do the following:

1. deliver onDataAvailabe to the decoder, to nsHTTPCompressConv, of the main thread.
2. the decoder should dispatch decoded data to the main thread.

we need to be careful to properly cancel data delivery from the decoder if channel gets canceled.

I think this should work.

So I ran some try runs of the patch I posted above (and some variants) to do some try runs and here are the results:

Always move off-main-thread, all decompression
This is the current version of the patch posted for review. If the listener chain for nsHTTPCompessConv doesn't support off-main-thread OnDataAvailable, nsHTTPCompressConv::OnDataAvailable will dispatch a task to call its listener on the main thread.
Regresses the following:

• raptor-tp6-imgur-firefox opt 4.06%
• raptor-tp6-instagram-firefox opt 27.92%
• raptor-tp6-linkedin-firefox opt 2%
• raptor-tp6-sheets-firefox opt 3%
• raptor-tp6-yahoo-news-firefox opt 2.62%

Only move off-main-thread when entire listener chain supports, all decompression
Regresses the following:

• raptor-tp6-imgur-firefox opt 5.18%
• raptor-tp6-instagram-firefox opt 28.44%
  Improves the following:
• raptor-tp6-wikipedia-firefox opt 2.28%
  Improves the following:
• raptor-tp6-google-firefox opt 3.10%

Always move off-main-thread, only Brotli
Like the patch posted for review, this will always re-target off-the-main thread and dispatch the listener back to the main thread when it doesn't support re-targeting.
Regresses the following:
raptor-tp6-facebook-firefox-cold opt 33.20%

Improves the following:

• raptor-tp6-google-firefox opt 3.15%
• raptor-tp6-reddit-firefox opt 3.48%
• raptor-tp6-youtube-firefox opt 3.10%

Only move off-main-thread when entire listener chain supports, only Brotli
Regresses the following:

• raptor-tp6-facebook-firefox-cold opt 49.73%
• raptor-tp6-imgur-firefox opt 4.44%
• raptor-tp6-instagram-firefox opt 30.12%
• raptor-tp6-linkedin-firefox opt 2.21%

I'm going to get this compiling again and re-evaluate it with our latest performance tests which include features like visual metrics.

Current nightly still seeing about 65ms in the content process during facebook pageload on a MacBook Pro.
https://share.firefox.dev/3eyoWLl

I've gotten the patches compiling again.

Nazim was kind enough to capture new profiles with these patches:

Baseline, 109ms of Brotli decompression on content process main thread:
https://share.firefox.dev/3ny3zhd

With Brotli moved omt: now only 4ms of Brotli decompression on content process main thread:
https://share.firefox.dev/3sXGHZx

Awaiting visual metric runs on try.

We have some interesting results from visual metrics.

I only rebuilt two of the variations from Comment 16
Always move off-main-thread, all decompression

While this regresses many sites, there are also numerous improvements of up to 50% in visual metrics.

Always move off-main-thread, only Brotli decompression

This regresses more sites than it improves, which is interesting.

I think a good next step would be to compare these variations on larger set of pages, ideally using live sites.

The Performance Priority Calculator has determined this bug's performance priority to be P1.

Platforms: macOS
Impact on site: Causes noticeable jank
Page load impact: Some
[x] Affects major website
[x] Able to reproduce locally

While this would be useful right now, to my understanding it will no longer be needed once we can move the network calls off the content process main thread, Bug 1639433.

The severity field for this bug is set to S3. However, the Performance Impact field flags this bug as having a high impact on the performance.
:jesup, could you consider increasing the severity of this performance-impacting bug? Alternatively, if you think the performance impact is lower than previously assessed, could you request a re-triage from the performance team by setting the Performance Impact flag to ??

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