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

[David Henningsson]

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