[pulseaudio-discuss] [PATCH] Fix unused buffer size to avoid xrun

[David Henningsson]

On 04/05/2012 10:59 AM, Feng Wei wrote:
> David,
> I'd met xrun on some embedded platform, which will only report hw_ptr
> at period boundary. Maybe it shouldn't use tsched, I'm not sure. Sorry
> for inconvenience.

Actually it does raise an important question about how we deal with 
platforms that have bad hw_ptr granularity. We don't to that very well 
today.

Also is there much difference, powersave wise, between running in 
non-tsched and tsched mode? If there isn't, maybe using non-tsched for 
your particular device is the best option (if it works).

>
> 2012/4/5 David Henningsson<david.henningsson at canonical.com>:
>> On 04/05/2012 10:22 AM, Feng Wei wrote:
>>>
>>> When set latency is less than period time, we will assgin working
>>> buffer less than a period size, which will cause unnecessary xrun
>>> and wrong message indicating alsa driver bug.
>>
>>
>> NAK, I don't think this is correct.
>>
>> This is tricky stuff though, so don't take my word for it! ;-)
>>
>> On what machine was this solving a problem for you?
>>
>> Have you verified it leads to better behaviour (or at least not worse) on
>> both tsched and non-tsched systems?
>>
>> I e, try a VOIP call with ~20 ms of latency, on a desktop machine that has 2
>> x 1s periods, running in tsched mode. I'm guessing the latency will be
>> unacceptable with this patch applied.
>>
>>>
>>> Signed-off-by: Feng Wei<feng.wei at linaro.org>
>>> ---
>>>   src/modules/alsa/alsa-sink.c   |    6 +++---
>>>   src/modules/alsa/alsa-source.c |    6 +++---
>>>   2 files changed, 6 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/src/modules/alsa/alsa-sink.c b/src/modules/alsa/alsa-sink.c
>>> index 5a4b606..a53fb6f 100644
>>> --- a/src/modules/alsa/alsa-sink.c
>>> +++ b/src/modules/alsa/alsa-sink.c
>>> @@ -953,10 +953,10 @@ static int update_sw_params(struct userdata *u) {
>>>
>>>               b = pa_usec_to_bytes(latency,&u->sink->sample_spec);
>>>
>>>
>>> -            /* We need at least one sample in our buffer */
>>> +            /* We need at least one period and one sample in our buffer
>>> to avoid underflow */
>>>
>>> -            if (PA_UNLIKELY(b<    u->frame_size))
>>> -                b = u->frame_size;
>>> +            if (PA_UNLIKELY(b<    u->frame_size + u->fragment_size))
>>> +                b = u->frame_size + u->fragment_size;
>>>
>>>               u->hwbuf_unused = PA_LIKELY(b<    u->hwbuf_size) ?
>>> (u->hwbuf_size - b) : 0;
>>>           }
>>> diff --git a/src/modules/alsa/alsa-source.c
>>> b/src/modules/alsa/alsa-source.c
>>> index 27fd3b9..8c41ca6 100644
>>> --- a/src/modules/alsa/alsa-source.c
>>> +++ b/src/modules/alsa/alsa-source.c
>>> @@ -876,10 +876,10 @@ static int update_sw_params(struct userdata *u) {
>>>
>>>               b = pa_usec_to_bytes(latency,&u->source->sample_spec);
>>>
>>>
>>> -            /* We need at least one sample in our buffer */
>>> +            /* We need at least one period and one sample in our buffer
>>> to avoid overflow */
>>>
>>> -            if (PA_UNLIKELY(b<    u->frame_size))
>>> -                b = u->frame_size;
>>> +            if (PA_UNLIKELY(b<    u->frame_size + u->fragment_size))
>>> +                b = u->frame_size + u->fragment_size;
>>>
>>>               u->hwbuf_unused = PA_LIKELY(b<    u->hwbuf_size) ?
>>> (u->hwbuf_size - b) : 0;
>>>           }
>>
>>
>>
>>
>> --
>> David Henningsson, Canonical Ltd.
>> http://launchpad.net/~diwic
>
>
>



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