On Wed, 03 May 2023 22:00:37 +0200, Oswald Buddenhagen wrote: > > On Wed, May 03, 2023 at 09:32:02PM +0200, Jaroslav Kysela wrote: > > On 03. 05. 23 18:10, Takashi Iwai wrote: > >> The dmix uses the silence_size=boundary as a fill-all operation, and > >> it's a free-wheel mode, so supposedly something was overlooked in your > >> code refactoring. > >> > >> Could you check it and address quickly? I'd like to fix it before > >> 6.4-rc1 release, so if no fix comes up in a couple of days, I'll have > >> to revert the change for 6.4-rc1. > > > > I would revert this patch. > > > It seems that this "do silence right after the playback is finished" > > mechanism is not handled in the updated code (and I overlooked that, > > too): > > > no, there is nothing wrong with the code _per se_. > > what's happening is that the dmix plugin doesn't update the > application pointer, and somehow gets away with it. > > that means that it would have never worked with thresholded silencing > mode, either, but, well, it uses top-up mode. Well, the code made just a wrong interpretation for the behavior with silence_size == boundary. This mode is actually a kind of tailored operation for dmix. In the description of alsa-lib snd_pcm_sw_params_set_silence_size(), you can find it: /** * \brief Set silence size inside a software configuration container * \param pcm PCM handle * \param params Software configuration container * \param val Silence size in frames (0 for disabled) * \return 0 otherwise a negative error code * * A portion of playback buffer is overwritten with silence when playback * underrun is nearer than silence threshold (see * #snd_pcm_sw_params_set_silence_threshold) * * The special case is when silence size value is equal or greater than * boundary. The unused portion of the ring buffer (initial written samples * are untouched) is filled with silence at start. Later, only just processed * sample area is filled with silence. Note: silence_threshold must be set to zero. */ So, the "top-up" silencing happens only at start, but not after that. In the code path of hw_ptr update, it doesn't check the appl_ptr any longer, but fills the processed area by the hw_ptr update with silence. That's the intended behavior for use cases of free-wheel mode without appl_ptr updates like dmix. Takashi
