[pulseaudio-discuss] [PATCH] loopback: Always use the trivial resampler.

[pl bossart]

> The sink may be running in a low-latency mode even if the loopback
> stream doesn't have any latency requirements - there may be other
> streams active at the same time with stricter timing requirements.
>
> FWIW, the practical case here was a very simple test of looping null
> sink's monitor to a hw sink with default settings on Harmattan. It may
> be that our setup is more suspectible to this kind of problems than
> "normal" systems, but I still think that non-realtime-safe stuff should
> be kept out of the IO threads, regardless of the setup, especially if
> such stuff can very well be done outside the IO thread.

if you are still using 10ms periods on the hw sinks, then yes it's an
artifical use case in a constrained environment that doesn't use
timer-based scheduling...
I don't disagree that doing SRC in an io thread is not that kosher,
but keep in mind that we also do mixing and volume control in the IO
thread. There is some amount of DSP in this thread which will impact
response time to hw events.
Maybe your idea of linking latency with SRC quality makes sense. I
feel however that the speex SRC is not up to snuff and results in high
CPU usage. If we fixed the SRC to use a 'reasonable' MHz figure this
problem would go away.

Loopback is used in Medfield for FM playback only. I haven't heard of
any issues. The only bugs on loopback I've seen are on erratic src
adjustments on BT A2DP and RTP RX, but I haven't tried since Maarten
contributed patches.
-Pierre