From f6ccfd5d166acf495f5d6d320da503fae8dc14a4 Mon Sep 17 00:00:00 2001 From: BALATON Zoltan Date: Sun, 16 Mar 2025 01:20:46 +0100 Subject: [PATCH] alsaaudio: Set try-poll to false by default MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Acked-by: Marc-André Lureau [ Marc-André - Updated QAPI and CLI doc ] Signed-off-by: Marc-André Lureau Message-Id: <20250316002046.D066A4E6004@zero.eik.bme.hu> --- audio/alsaaudio.c | 2 +- qapi/audio.json | 2 +- qemu-options.hx | 4 ++-- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/audio/alsaaudio.c b/audio/alsaaudio.c index cacae1ea59..9b6c01c0ef 100644 --- a/audio/alsaaudio.c +++ b/audio/alsaaudio.c @@ -899,7 +899,7 @@ static void alsa_enable_in(HWVoiceIn *hw, bool enable) static void alsa_init_per_direction(AudiodevAlsaPerDirectionOptions *apdo) { if (!apdo->has_try_poll) { - apdo->try_poll = true; + apdo->try_poll = false; apdo->has_try_poll = true; } } 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 ## diff --git a/qemu-options.hx b/qemu-options.hx index aab53bcfe8..7eb8e02b4b 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -965,7 +965,7 @@ SRST Sets the period length in microseconds. ``in|out.try-poll=on|off`` - Attempt to use poll mode with the device. Default is on. + Attempt to use poll mode with the device. Default is off. ``threshold=threshold`` Threshold (in microseconds) when playback starts. Default is 0. @@ -1002,7 +1002,7 @@ SRST ``in|out.buffer-count=count`` Sets the count of the buffers. - ``in|out.try-poll=on|of`` + ``in|out.try-poll=on|off`` Attempt to use poll mode with the device. Default is on. ``try-mmap=on|off`` -- 2.39.5