[pulseaudio-discuss] [PATCH] module-virtual-sink: Speed up draining

[David Henningsson]

On 2014-10-19 12:57, Tanu Kaskinen wrote:
> On Thu, 2014-10-02 at 15:58 +0200, David Henningsson wrote:
>> The drain speed increase done a while ago, only worked when directly connected
>> to ALSA sinks. Playing through an module-virtual-sink would cause slower drains.
>
> What about other virtual sinks? Shouldn't the same fix be applied to
> those too?

Yes, but let's start with the simplest case first.

>> This fix has two parts:
>>   1) We now refuse to process handed out silence. This has the effect
>>      that it tells ALSAs sink input that we're draining, and that we want to
>
> s/ALSAs sink input/the ALSA sink/ ?

Both, module-virtual-sink has an "alsa sink input" which in turn tells 
the alsa sink.

>>      be woken up exactly at this sample based point in time.
>>   2) When we're being called to process input underruns, we know this has
>>      happened, so we can just forward the call up the sink chain to get
>>      to protocol-native, which can acknowledge that the drain has completed.
>>
>> This fix is incomplete, because if more than one sink input is playing back
>> into the sink, only the last one will be drained in time. But it's better
>> than nothing.
>
> A comment about this shortcoming in the code would be good.

Ok.

>> Signed-off-by: David Henningsson <david.henningsson at canonical.com>
>> ---
>>
>> Happy for testing of this patch - Ubuntu runs HDA-intel with 64K buffers instead of the 2M that
>> some distros use, so I'm not seeing that much difference that you do anyway.
>
> The buffer size can be changed at runtime:
> echo 2048 > /proc/asound/card0/pcm0p/sub0/prealloc

Right, I keep forgetting about that.

>> Also, when I was testing, I also noticed a bigger startup latency when playing
>> back through a virtual sink. This is nothing I have looked deeper at.
>>
>>   src/modules/module-virtual-sink.c | 22 ++++++++++++++++++++++
>>   1 file changed, 22 insertions(+)
>>
>> diff --git a/src/modules/module-virtual-sink.c b/src/modules/module-virtual-sink.c
>> index 66fd8a9..c1e5969 100644
>> --- a/src/modules/module-virtual-sink.c
>> +++ b/src/modules/module-virtual-sink.c
>> @@ -216,6 +216,10 @@ static int sink_input_pop_cb(pa_sink_input *i, size_t nbytes, pa_memchunk *chunk
>>           pa_memchunk nchunk;
>>
>>           pa_sink_render(u->sink, nbytes, &nchunk);
>> +        if (nchunk.memblock == u->sink->silence.memblock) {
>> +            pa_memblock_unref(nchunk.memblock);
>> +            return -1;
>> +        }
>
> I think this needs a comment explaining what it implies if
> pa_sink_render() returns silence and why it makes sense to return -1 in
> that case.

Ok.

-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic