1421148 - CPU usage on idle YouTube video playback multiplies under High Performance power profile

Status: UNCONFIRMED

(Core :: Audio/Video: Playback, defect, P3)

Description

[smartfon.reddit]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20171123161455

Steps to reproduce:

CPU usage is 2-3x higher during an idle playback with High Performance power profile on Windows 10, compared to Balanced profile. Is this supposed to be this way? Sometimes the fans will swirl loud. Other browsers use much less power.

Intel i7-7700HQ with VP9 hardware/software decoding with the latest graphics drivers. Tested on this video at 720p https://www.youtube.com/watch?v=Dls5srDb2pI
I've created fresh power profiles under Power Options with default Windows 10 settings.

Firefox & Balanced = 3.6%
Firefox & Performance = 8.5%
Chrome & Balanced = 1.7%
Chrome & Performance = 3.5%

With Firefox & Balanced, this is the Task Manager https://i.imgur.com/Vx82PsO.png
There are no child processes that constantly use the graphics. Child 1 and 3 only appear under "GPU" tab a for a split of a second then disappear. 

With Firefox & Performance, this is the Task Manager https://i.imgur.com/DkwMGDJ.png
Child 1 and 3 constantly use graphics and they appear to be responsible for the increased CPU usage too.

If I reduce Performance profile's CPU processor state from 100% Min/100% Max to 70% both, https://i.imgur.com/D1sWGZW.png
I'll get similar low CPU usage on YouTube as in Balanced mode.

70%/70% = low CPU (Performance profile)
5%/70% = low CPU (Performance profile)
5%/100% = high CPU (Performance profile)
5%/100% = low CPU (Balanced profile)

Balanced profile also has 5%/100% setup, yet it has low CPU usage. This means there is something else under Performance profile that's responsible for higher CPU, not the fact that its Max is 100%.

Forgive me if this is an obvious thing and it's supposed to be this way, but why does Performance use much more power while playing an idle video? I'd expect high CPU while loading the page, then a reduction to lower single digits once the page has finished loading, just like in Balanced mode. Hence the decision to file a bug report just in case.
This is not a new problem. It's unrelated to new software installation or updates. I'm only discovering that power profile is the culprit after many months of investigation to increase the battery life.  

Related conversation https://www.reddit.com/r/firefox/comments/7fphoa/i_found_the_reason_why_firefox_uses_3x_more_cpu/

Comment 1

[Anthony Jones (:ajones, :kentuckyfriedtakahe, :k17e)]

Firefox uses ffvp9 which is more parallel than libvpx and therefore can decode a higher peak framerate, it therefore shouldn't come as a surprise to see different figures from other browsers. Edge and Chrome both use libvpx. You could try setting media.ffvpx.enabled=false if you want to figure out if it is the browser or the decoder.

There may also be differences in the graphics path, so can you please attach the information from about:support ?

Comment 2

[smartfon.reddit]

Attachment: about_support.txt

Comment 3

[smartfon.reddit]

(In reply to Anthony Jones (:kentuckyfriedtakahe, :k17e) from comment #1)

No difference with media.ffvpx.enabled=false.

Comment 4

[Graham Perrin]

1445470 - [tracking] video playback performance
<https://bugzilla.mozilla.org/show_bug.cgi?id=1445470>