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

[Pierre-Louis Bossart]

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);
-- 
1.7.6.5