[alsa-devel] [PATCHv2 1/1] pcm_pulse: set prebuf parameter according to software parameters

[David Henningsson]

On 11/19/2012 07:09 PM, Takashi Iwai wrote:
> At Sun, 18 Nov 2012 12:01:49 +0200,
> 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.
>
> Looks good to me.  David, could you review?

I think so too.

Acked-by: David Henningsson <david.henningsson at canonical.com>

> Also, the first patch isn't needed, right?

I think the "pcm_pulse: do not trigger immediately at start" patch 
should not be applied.

>
>
> Takashi
>
>> ---
>>   pulse/pcm_pulse.c |   32 ++++++++++++++++++++++++++++++--
>>   1 file changed, 30 insertions(+), 2 deletions(-)
>>
>> diff --git a/pulse/pcm_pulse.c b/pulse/pcm_pulse.c
>> index 24fd4da..4226d30 100644
>> --- a/pulse/pcm_pulse.c
>> +++ b/pulse/pcm_pulse.c
>> @@ -854,8 +854,9 @@ static int pulse_hw_params(snd_pcm_ioplug_t * io,
>>   		4 * 1024 * 1024;
>>   	pcm->buffer_attr.tlength =
>>   		io->buffer_size * pcm->frame_size;
>> -	pcm->buffer_attr.prebuf =
>> -	    (io->buffer_size - io->period_size) * pcm->frame_size;
>> +	if (pcm->buffer_attr.prebuf == (uint32_t)-1)
>> +		pcm->buffer_attr.prebuf =
>> +			(io->buffer_size - io->period_size) * pcm->frame_size;
>>   	pcm->buffer_attr.minreq = io->period_size * pcm->frame_size;
>>   	pcm->buffer_attr.fragsize = io->period_size * pcm->frame_size;
>>
>> @@ -865,6 +866,31 @@ 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);
>> +
>> +	/* At least one period to keep PulseAudio happy */
>> +	if (start_threshold < io->period_size)
>> +		start_threshold = io->period_size;
>> +
>> +	pcm->buffer_attr.prebuf = start_threshold * pcm->frame_size;
>> +
>> +	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;
>> @@ -931,6 +957,7 @@ 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
>>   };
>> @@ -1088,6 +1115,7 @@ SND_PCM_PLUGIN_DEFINE_FUNC(pulse)
>>   	}
>>
>>   	pcm->handle_underrun = handle_underrun;
>> +	pcm->buffer_attr.prebuf = -1;
>>
>>   	err = pulse_connect(pcm->p, server, fallback_name != NULL);
>>   	if (err < 0)
>> --
>> 1.7.10.4
>>
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>> Alsa-devel at alsa-project.org
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>>
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-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic