Hi On Mon, May 26, 2025 at 8:27 AM Markus Armbruster <arm...@redhat.com> wrote:
> marcandre.lur...@redhat.com writes: > > > From: BALATON Zoltan <bala...@eik.bme.hu> > > > > 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 <bala...@eik.bme.hu> > > Acked-by: Marc-André Lureau <marcandre.lur...@redhat.com> > > [ Marc-André - Updated QAPI and CLI doc ] > > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com> > > Message-Id: <20250316002046.d066a4e6...@zero.eik.bme.hu> > > --- > > 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? > > I doubt anyone will care as long as it doesn't break (that we can't know). I added a note to https://wiki.qemu.org/ChangeLog/10.1#Audio We normally record incompatible changes in docs/about/deprecated.rst and > then docs/about/removed-features.rst, but these don't fit here. > > [...] > >
