[email protected] writes: > From: BALATON Zoltan <[email protected]> > > Quoting Volker Rümelin: "try-poll=on tells the ALSA backend to try to > use an event loop instead of the audio timer. This works most of the > time. But the poll event handler in the ALSA backend has a bug. For > example, if the guest can't provide enough audio frames in time, the > ALSA buffer is only partly full and the event handler will be called > again and again on every iteration of the main loop. This increases > the processor load and the guest has less processor time to provide > new audio frames in time. I have two examples where a guest can't > recover from this situation and the guest seems to hang." > > One reproducer I've found is booting MorphOS demo iso on > qemu-system-ppc -machine pegasos2 -audio alsa which should play a > startup sound but instead it freezes. Even when it does not hang it > plays choppy sound. Volker suggested using command line to set > try-poll=off saying: "The try-poll=off arguments are typically > necessary, because the alsa backend has a design issue with > try-poll=on. If the guest can't provide enough audio frames, it's > really unhelpful to ask for new audio frames on every main loop > iteration until the guest can provide enough audio frames. Timer based > playback doesn't have that problem." > > But users cannot easily find this option and having a non-working > default is really unhelpful so to make life easier just set it to > false by default which works until the issue with the alsa backend can > be fixed. > > Signed-off-by: BALATON Zoltan <[email protected]> > Acked-by: Marc-André Lureau <[email protected]> > [ Marc-André - Updated QAPI and CLI doc ] > Signed-off-by: Marc-André Lureau <[email protected]> > Message-Id: <[email protected]> > --- > qapi/audio.json | 2 +- > audio/alsaaudio.c | 2 +- > qemu-options.hx | 4 ++-- > 3 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/qapi/audio.json b/qapi/audio.json > index dd5a58d13e..49633cf317 100644 > --- a/qapi/audio.json > +++ b/qapi/audio.json > @@ -96,7 +96,7 @@ > # @period-length: the period length in microseconds > # > # @try-poll: attempt to use poll mode, falling back to non-polling > -# access on failure (default true) > +# access on failure (default false) > # > # Since: 4.0 > ##
Missed this when it was posted (it wasn't cc'ed to me). Flipping the default is technically an incompatible change. I understand the justification, and I'm not passing judgement on its validity; that's the audio maintainers job. I just want to ask: does this need a release note? We normally record incompatible changes in docs/about/deprecated.rst and then docs/about/removed-features.rst, but these don't fit here. [...]
