[pulseaudio-discuss] [PATCH] alsa: get avail, delay, timestamps in a single kernel call

[David Henningsson]

Hi Pierre,

sorry for the long delay.

This seems to make a lot of sense, but a question - does this impose a 
requirement on a certain version of alsa-lib and/or the linux kernel?

// David


2012-07-30 02:46, Pierre-Louis Bossart skrev:
> Refactor code to fetch avail, delay and timestamp values
> in a single call to snd_pcm_status().
> The information reported is exactly the same as before,
> however it is extracted in a more atomic manner to
> improve timer-based scheduling.
>
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> ---
>   src/modules/alsa/alsa-sink.c   |   12 ++++--------
>   src/modules/alsa/alsa-source.c |   12 ++++--------
>   src/modules/alsa/alsa-util.c   |   17 ++++++++++++-----
>   src/modules/alsa/alsa-util.h   |    2 +-
>   4 files changed, 21 insertions(+), 22 deletions(-)
>
> diff --git a/src/modules/alsa/alsa-sink.c b/src/modules/alsa/alsa-sink.c
> index 544399e..e4baa1f 100644
> --- a/src/modules/alsa/alsa-sink.c
> +++ b/src/modules/alsa/alsa-sink.c
> @@ -825,6 +825,7 @@ static void update_smoother(struct userdata *u) {
>       int err;
>       pa_usec_t now1 = 0, now2;
>       snd_pcm_status_t *status;
> +    snd_htimestamp_t htstamp = { 0, 0 };
>   
>       snd_pcm_status_alloca(&status);
>   
> @@ -833,18 +834,13 @@ static void update_smoother(struct userdata *u) {
>   
>       /* Let's update the time smoother */
>   
> -    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, &delay, u->hwbuf_size, &u->sink->sample_spec, FALSE)) < 0)) {
> +    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, status, &delay, u->hwbuf_size, &u->sink->sample_spec, FALSE)) < 0)) {
>           pa_log_warn("Failed to query DSP status data: %s", pa_alsa_strerror(err));
>           return;
>       }
>   
> -    if (PA_UNLIKELY((err = snd_pcm_status(u->pcm_handle, status)) < 0))
> -        pa_log_warn("Failed to get timestamp: %s", pa_alsa_strerror(err));
> -    else {
> -        snd_htimestamp_t htstamp = { 0, 0 };
> -        snd_pcm_status_get_htstamp(status, &htstamp);
> -        now1 = pa_timespec_load(&htstamp);
> -    }
> +    snd_pcm_status_get_htstamp(status, &htstamp);
> +    now1 = pa_timespec_load(&htstamp);
>   
>       /* Hmm, if the timestamp is 0, then it wasn't set and we take the current time */
>       if (now1 <= 0)
> diff --git a/src/modules/alsa/alsa-source.c b/src/modules/alsa/alsa-source.c
> index 94d4a09..17566e7 100644
> --- a/src/modules/alsa/alsa-source.c
> +++ b/src/modules/alsa/alsa-source.c
> @@ -767,6 +767,7 @@ static void update_smoother(struct userdata *u) {
>       int err;
>       pa_usec_t now1 = 0, now2;
>       snd_pcm_status_t *status;
> +    snd_htimestamp_t htstamp = { 0, 0 };
>   
>       snd_pcm_status_alloca(&status);
>   
> @@ -775,18 +776,13 @@ static void update_smoother(struct userdata *u) {
>   
>       /* Let's update the time smoother */
>   
> -    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, &delay, u->hwbuf_size, &u->source->sample_spec, TRUE)) < 0)) {
> +    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, status, &delay, u->hwbuf_size, &u->source->sample_spec, TRUE)) < 0)) {
>           pa_log_warn("Failed to get delay: %s", pa_alsa_strerror(err));
>           return;
>       }
>   
> -    if (PA_UNLIKELY((err = snd_pcm_status(u->pcm_handle, status)) < 0))
> -        pa_log_warn("Failed to get timestamp: %s", pa_alsa_strerror(err));
> -    else {
> -        snd_htimestamp_t htstamp = { 0, 0 };
> -        snd_pcm_status_get_htstamp(status, &htstamp);
> -        now1 = pa_timespec_load(&htstamp);
> -    }
> +    snd_pcm_status_get_htstamp(status, &htstamp);
> +    now1 = pa_timespec_load(&htstamp);
>   
>       /* Hmm, if the timestamp is 0, then it wasn't set and we take the current time */
>       if (now1 <= 0)
> diff --git a/src/modules/alsa/alsa-util.c b/src/modules/alsa/alsa-util.c
> index bb4e307..4a29a9a 100644
> --- a/src/modules/alsa/alsa-util.c
> +++ b/src/modules/alsa/alsa-util.c
> @@ -1141,10 +1141,11 @@ snd_pcm_sframes_t pa_alsa_safe_avail(snd_pcm_t *pcm, size_t hwbuf_size, const pa
>       return n;
>   }
>   
> -int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_sframes_t *delay, size_t hwbuf_size, const pa_sample_spec *ss, pa_bool_t capture) {
> +int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_status_t *status, snd_pcm_sframes_t *delay, size_t hwbuf_size, const pa_sample_spec *ss,
> +                       pa_bool_t capture) {
>       ssize_t k;
>       size_t abs_k;
> -    int r;
> +    int err;
>       snd_pcm_sframes_t avail = 0;
>   
>       pa_assert(pcm);
> @@ -1154,10 +1155,16 @@ int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_sframes_t *delay, size_t hwbuf_si
>   
>       /* Some ALSA driver expose weird bugs, let's inform the user about
>        * what is going on. We're going to get both the avail and delay values so
> -     * that we can compare and check them for capture */
> +     * that we can compare and check them for capture.
> +     * This is done with snd_pcm_status() which provides
> +     * avail, delay and timestamp values in a single kernel call to improve
> +     * timer-based scheduling */
>   
> -    if ((r = snd_pcm_avail_delay(pcm, &avail, delay)) < 0)
> -        return r;
> +    if ((err = snd_pcm_status(pcm, status)) < 0)
> +        return err;
> +
> +    avail = snd_pcm_status_get_avail(status);
> +    *delay = snd_pcm_status_get_delay(status);
>   
>       k = (ssize_t) *delay * (ssize_t) pa_frame_size(ss);
>   
> diff --git a/src/modules/alsa/alsa-util.h b/src/modules/alsa/alsa-util.h
> index a4beed2..236a329 100644
> --- a/src/modules/alsa/alsa-util.h
> +++ b/src/modules/alsa/alsa-util.h
> @@ -125,7 +125,7 @@ int pa_alsa_recover_from_poll(snd_pcm_t *pcm, int revents);
>   pa_rtpoll_item* pa_alsa_build_pollfd(snd_pcm_t *pcm, pa_rtpoll *rtpoll);
>   
>   snd_pcm_sframes_t pa_alsa_safe_avail(snd_pcm_t *pcm, size_t hwbuf_size, const pa_sample_spec *ss);
> -int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_sframes_t *delay, size_t hwbuf_size, const pa_sample_spec *ss, pa_bool_t capture);
> +int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_status_t *status, snd_pcm_sframes_t *delay, size_t hwbuf_size, const pa_sample_spec *ss, pa_bool_t capture);
>   int pa_alsa_safe_mmap_begin(snd_pcm_t *pcm, const snd_pcm_channel_area_t **areas, snd_pcm_uframes_t *offset, snd_pcm_uframes_t *frames, size_t hwbuf_size, const pa_sample_spec *ss);
>   
>   char *pa_alsa_get_driver_name(int card);


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