On 11/14/2012 07:07 PM, Rémi Denis-Courmont wrote:
The current default value for prebuf is very high, almost the full virtual ALSA buffer. This breaks some application especially where low latency is involved.
This patch makes pcm_pulse implement the sw_params callback and get the prebuf value from the ALSA software parameters. Thus the trigger latency is much more like what an ALSA application should expect from an ALSA PCM device.
This seems reasonable I believe; see review comments below.
pulse/pcm_pulse.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)
diff --git a/pulse/pcm_pulse.c b/pulse/pcm_pulse.c index 0165120..08b6cea 100644 --- a/pulse/pcm_pulse.c +++ b/pulse/pcm_pulse.c @@ -859,6 +859,30 @@ static int pulse_hw_params(snd_pcm_ioplug_t * io, return err; }
+static int pulse_sw_params(snd_pcm_ioplug_t *io, snd_pcm_sw_params_t *params) +{
- snd_pcm_pulse_t *pcm = io->private_data;
- snd_pcm_uframes_t start_threshold;
- assert(pcm);
- if (!pcm->p || !pcm->p->mainloop)
return -EBADFD;- pa_threaded_mainloop_lock(pcm->p->mainloop);
- snd_pcm_sw_params_get_start_threshold(params, &start_threshold);
- if (start_threshold < io->period_size)
start_threshold = io->period_size;
Why do we need the above constraint?
- pcm->buffer_attr.prebuf = start_threshold * pcm->frame_size;
This works only if sw_params is set after hw_params. It would be better if the patch could handle also if hw_params is set after sw_params.
- pa_threaded_mainloop_unlock(pcm->p->mainloop);
- return 0;
+}
- static int pulse_close(snd_pcm_ioplug_t * io) { snd_pcm_pulse_t *pcm = io->private_data;
@@ -925,6 +949,7 @@ static const snd_pcm_ioplug_callback_t pulse_playback_callback = { .poll_revents = pulse_pcm_poll_revents, .prepare = pulse_prepare, .hw_params = pulse_hw_params,
- .sw_params = pulse_sw_params, .close = pulse_close, .pause = pulse_pause };