Audio buffer underruns with ALSA (probably caused by alsartfix)

[Marco]

Since about 2 weeks, I have encountered some issues with increased audio buffer underruns in recent commits of Mixxx. Especially when I load a song into a deck while the other deck is playing, or open a dialog (e.g. settings), or playing song with key pitch enabled, or even when I'm browsing through the song library too fast.
Before this I've used commit 37a6a5327e23d24c3539ec22ad571af93a0705f4 even for gigs in my productive environment without any noticeable underruns even under heavy load.

So yesterday I've spent some time to find out what's the culprit for this issue. The last commit that works at least for me is https://github.com/mixxxdj/mixxx/tree/48781daed114e652338ffba76a3f4b6b4ab5beeb. The issue starts with https://github.com/mixxxdj/mixxx/tree/5d3c4670d6060ccb31da465a5cab7651803ac365 and all further commits. The culprit seems to be the alsartfix (https://github.com/mixxxdj/mixxx/pull/3160), so I did a quick test compiling the latest commit (9ddc5ae7bf38a26103f5d788ff2c3de72d795eae) and reverted all changes concerning the alsartfix. Et voila... everything is working again as expected.

I'm using ALSA directly (without Pulseaudio) and a Denon MC7000 controller. Kernel is 5.4 with applied and working RT patch (Gentoo Linux 64 Bit).

Thanks in advance!
Regards,
Marco

[Uwe Klotz (uklotzde-deactivatedaccount)]

https://github.com/mixxxdj/mixxx/pull/3277

[Be (be.ing)]

Thank you for taking the time to investigate the source of the issue.

[Uwe Klotz (uklotzde-deactivatedaccount)]

Thank you also from my side. Your thorough investigation and analysis was the base for finding the source of this critical issue quickly! Hopefully fixed now.

[Marco (c-moon)]

You're welcome, guys! Glad to hear that I could help to narrow down this issue for good.
But I'm still wondering why no one else has noticed this problem before? But to be honest, when these issues have occurred the first time here, I thought there must be something wrong with my setup. Until I tried an earlier version of Mixxx and realized the buffer underruns are suddenly all gone.
Thanks again for your excellent work on Mixxx!

[Be (be.ing)]

https://github.com/mixxxdj/mixxx/pull/3160 was merged only 17 days ago and there has not been any releases since then, so that's why no else has reported this. Personally I use JACK so I wasn't affected by this.

[Marco (c-moon)]

OK, so it's very helpful then that I'm always compiling recent Git commits myself. I will keep it up. ;-)

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/10206