After moving from Sarpi kernel/modules 4.19.34 to any newer kernel/modules, I started experiencing audio stuttering in Retroarch when launching any game. The stuttering would normally stop after some minutes of running the game. Displaying the framerate on the screen showed that framerate was below 60fps while the stuttering was going on.

Having sound disabled (which happened accidentally when a recent kernel broke the sound module) allowed a normal 60fps framerate. This suggested that the problem was with sound, and I ran across a report of someone having the same issue on an RPi4 so it didn't appear the issue was a performance/computing limitation of the RPi3.

For months I tried various retroarch.cfg settings, changing the selected audio driver, trying different audio/video sync settings and various other suggested tweaks. Nothing helped.

Today, completely by accident (I don't remember how in fact), I ran across a post discussing how to fix audio stutter in Steam on a Raspberry Pi:

https://steamcommunity.com/app/35338...2464753800526/

It suggested to edit /etc/pulse/default.pa

And change this line:

to:

After making this change and rebooting, the change can be verified by running this command below and looking for tsched=no in the ouput:

Accorcing to the ArchWiki, tsched controls how audio scheduling is done, and this section is relevant:
As to why it was newer kernels that made this problem appear? No idea. Maybe some change in kernel timing/scheduling behavior that somehow impacted the sound timing. Or maybe the ALSA driver that comes with newer kernels/modules exposes some issue which is triggered if tsched is enabled.

Total luck finding this solution - not something I'd ever figure out in this lifetime.

References:

Raspberry pi 4 poor audio, stuttering potential fix
https://steamcommunity.com/app/35338...2464753800526/

For pulseaudio what does tsched do (and what are the defaults)?
https://askubuntu.com/questions/371595

PulseAudio/Troubleshooting -> Glitches, skips or crackling
https://wiki.archlinux.org/index.php...roubleshooting

This fix is reported (in the Steam forum post) to help not just with Steam and Retroarch, but also with sound in various browsers (playing videos etc), and in rdesktop.

This is quite interesting. I've done some reading into this and learned a thing or two. Not being much of a desktop user on Slackware ARM, Raspberry Pi sound output isn't something I deal with, ever.

It seems there may be inferences for tsched on ARM64. That's certainly something to watch for the future.

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