[pulseaudio-tickets] [Bug 49608] periodic audio skips with Intel HDA

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=49608

--- Comment #57 from rkfg <rkfg at rkfg.me> ---
Some more info. On my new laptop that also has a VIA sound chipset I managed to
greatly leverage the problem by installing the low-latency Ubuntu kernel. I
have Ubuntu MATE 14.04 on it so it was effortless. Unfortunately, for
(presumably) performance reasons it doesn't have CONFIG_SND_PCM_XRUN_DEBUG
enabled so I can't see if it also misses interrupts. However, on the default
stock kernel which has this option it misses interrupts indeed. I tried various
position_fix and enable_msi values and nothing helped. I had underruns in the
log while doing usual things like opening sites, now on the low-latency kernel
it's all good even on PA's timer-based scheduling.

I can only guess but it could be because the CPU has only two cores and
sometimes it can't schedule an interrupt in time. The low-latency kernel has
1000 Hz timer compared to 250 Hz in the default one. It also has various
NO_HZ_* options enabled. I'll try two options on Monday with my own kernel for
Debian: one would be using the BFS scheduler and another one will feature
CONFIG_NO_HZ_FULL_ALL and alike options which are disabled when BFS is used.
I'll check if either of them will help with the missed interrupts.

The problem as I see it is that my work PC and this laptop isn't powerful
enough to server IRQs in time. They both have VIA sound although a bit
different models and 2 core CPUs. My home PC has 4 cores that are also more
powerful. I tried to output some sound via PA to its Realtek ALC889 card and
enabled xrun_debug. There were no messages about lost interrupts and I'm using
the same kernel that's used on the work PC. So the different behavior is either
because of different codecs/chipsets or CPUs.

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