Watt the fox?

How do websites waste CPU and Battery and Firefox cycles in Firefox

by H43Z

I recently got a new notebook and noticed that speakers sometimes released a weak but annoying white noise. This issue was found only in a quiet room without music or other audio playing speakers.

After digging, I found the following command

pactl list sinks short

(Check powercfg / Windows Requests?!)

This command lists all available audio sunks for Pulseaudio in Linux with their current status. States can be one of the following: idle, suspended, or run.

I find that speakers remain silent if the audio sink is in suspended condition. However, white noise occurs when the sink is in lazy or running, even if no music or sound is played.

Although I have a setting to automatically suspend audio after 10 seconds inactive:

% grep -R module-suspend-on-idle /etc/pulse/
/etc/pulse/default.pa:load-module module-suspend-on-idle
/etc/pulse/system.pa:load-module module-suspend-on-idle

But sometimes, the sink never wasted and therefore never had been suspended.

Manual for module-suspind-on-idle says:

Since 0.9.11. Disconnects sinks and sources from their backend after a
predetermined amount of idle time. Idle time is accumulated when the sink/source
in question is not connected to any streams.

Advantages: Saves power. ALSA uses considerably more CPU cycles when pulseaudio
has to send empty data to the soundcard during idle. If you don't plan to have
an active stream all the time, set the timer to a low value for best power savings.

I started using the command:

pactl list sink-inputs

Whenever I noticed the white noise, trying to figure out which program uses the audio sink.

It turns out to be Firefox. However, no one of the open tabs should play any sound-not even muted videos.

To get the reason for what happened, I made a small script for my i3 status bar. The script shows a red indicator at a time when the audio sinking went into a running condition.

Culprit looks like a notice sound from my pinned tab to Outlook.office.com. Whenever I received an email, the white noise starts and never stop until the tab is reloaded or restarted firefox.

This issue is not just about the annoying white noise – it also drains my notebook battery.

Here is the CPU / Power Consume without the white noise:

$ htop -F pulseaudio
    PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+ ▽Command
   3770 h43z        9 -11 1094M 30924 21580 S  0.0  0.1 10:57.51 /usr/bin/pulseaudio --daemonize=no --log-target=journal

$ powerstat -d0 3
  Time    User  Nice   Sys  Idle    IO  Run Ctxt/s  IRQ/s  Watts
20:54:31   0.8   0.1   0.5  98.6   0.0    1    957    900   4.42
20:54:34   0.0   0.1   0.2  99.7   0.0    1    728    591   4.34
20:54:37   0.3   0.1   1.3  98.2   0.1    1   1444   1241   4.32
20:54:40   0.0   0.1   0.1  99.8   0.0    1    695    556   4.46
20:54:43   0.4   0.1   0.4  99.1   0.0    1   1322    935   5.08
20:54:46   0.1   0.1   0.4  99.4   0.0    1   1216    944   4.50
20:54:49   0.0   0.1   0.1  99.8   0.0    1   1032    742   4.45
20:54:52   0.0   0.1   0.2  99.7   0.1    1    952    667   4.44
20:54:55   0.0   0.0   0.3  99.7   0.0    1    873    676   4.31
20:54:58   0.2   0.1   1.1  98.4   0.1    1   1508   1244   4.26
20:55:01   0.1   0.1   0.3  99.5   0.0    1   1191    877   4.42
20:55:04   0.1   0.1   0.3  99.6   0.0    1    994    757   4.44
20:55:07   0.6   0.1   0.3  99.0   0.0    1   1304    947   4.20
20:55:10   0.1   0.1   0.2  99.6   0.0    1    953    696   4.30
20:55:13   0.0   0.2   0.3  99.5   0.0    1    903    701   4.17

$ htop -F pulseaudio
    PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+ ▽Command
   3770 h43z        9 -11 1094M 30924 21580 S  4.7  0.1 10:56.31 /usr/bin/pulseaudio --daemonize=no --log-target=journal

$ powerstat -d0 3
  Time    User  Nice   Sys  Idle    IO  Run Ctxt/s  IRQ/s  Watts
20:52:42   0.7   0.1   1.3  98.0   0.0    1   3460   1542   5.98
20:52:45   0.7   0.1   1.4  97.8   0.0    2   3723   1788   6.00
20:52:48   0.7   0.1   1.4  97.8   0.0    3   3487   1719   5.99
20:52:51   1.1   0.1   1.4  97.5   0.0    1   3916   1861   6.34
20:52:54   0.6   0.1   1.3  98.0   0.0    1   3514   1692   5.89
20:52:57   0.7   0.1   1.8  97.3   0.1    1   3956   2067   6.57
20:53:00   0.8   0.1   1.1  98.0   0.0    1   3534   1522   5.88
20:53:03   0.6   0.1   1.2  98.0   0.0    1   3437   1626   5.87
20:53:06   0.7   0.0   1.2  98.0   0.0    1   3400   1700   5.94
20:53:09   0.8   0.1   1.3  97.9   0.0    2   3474   1421   5.88
20:53:12   0.7   0.1   1.2  98.0   0.0    1   3317   1441   5.84
20:53:15   1.3   0.1   1.6  97.0   0.0    4   3841   1777   5.83
20:53:18   1.1   0.1   1.6  97.1   0.1    1   4161   1906   5.87
20:53:21   0.7   0.1   1.3  97.9   0.0    1   3422   1505   5.90
20:53:24   1.5   0.1   1.7  96.8   0.0    3   3430   1707   5.91
20:53:27   0.7   0.1   1.3  97.9   0.0    1   3375   1511   6.73
20:53:30   0.7   0.0   1.2  98.0   0.0    1   3572   1563   6.13

const audioCtx = new AudioContext();

AudioContext.suspend()
Suspends the progression of time in the audio context, temporarily halting
audio hardware access and reducing CPU/battery usage in the process.

AudioContext.resume()
Resumes the progression of time in an audio context that has previously
been suspended.