[pulseaudio-discuss] [PATCH] alsa: disable period wakeups in tsched mode if possible

[Pierre-Louis Bossart]

This patch reflects a new capability that Lennart was wishing
for. Wish granted...

Re-submitting it now that alsa-lib 1.0.24
provides additional entry points to disable period
wakeups in timer-scheduling mode if hardware can
work without it (HDAudio, oxygen and Intel SST).

    Example with standard playback on HDAudio output
    Before change:

    Top causes for wakeups:
       3.8% (  5.4)   [hda_intel] <interrupt>
       2.8% (  4.0)   alsa-sink

    After change:
    Top causes for wakeups:
       2.3% (  3.0)   alsa-sink

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at intel.com>
---
 src/modules/alsa/alsa-util.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/src/modules/alsa/alsa-util.c b/src/modules/alsa/alsa-util.c
index 5a726ff..786e664 100644
--- a/src/modules/alsa/alsa-util.c
+++ b/src/modules/alsa/alsa-util.c
@@ -251,6 +251,22 @@ int pa_alsa_set_hw_params(
     if (!pa_alsa_pcm_is_hw(pcm_handle))
         _use_tsched = FALSE;
 
+#if (SND_LIB_VERSION >= ((1<<16)|(0<<8)|24)) /* API additions in 1.0.24 */
+    if (_use_tsched) {
+
+        /* try to disable period wakeups if hardware can do so */
+        if (snd_pcm_hw_params_can_disable_period_wakeup(hwparams)) {
+
+            if (snd_pcm_hw_params_set_period_wakeup(pcm_handle, hwparams, FALSE) < 0)
+                /* don't bail, keep going with default mode with period wakeups */
+                pa_log_debug("snd_pcm_hw_params_set_period_wakeup() failed: %s", pa_alsa_strerror(ret));
+            else
+                pa_log_info("Trying to disable ALSA period wakeups, using timers only");
+        } else
+            pa_log_info("cannot disable ALSA period wakeups");
+    }
+#endif
+
     if ((ret = set_format(pcm_handle, hwparams, &_ss.format)) < 0)
         goto finish;
 
@@ -378,6 +394,18 @@ success:
         goto finish;
     }
 
+#if (SND_LIB_VERSION >= ((1<<16)|(0<<8)|24)) /* API additions in 1.0.24 */
+    if (_use_tsched) {
+        unsigned int no_wakeup;
+        /* see if period wakeups were disabled */
+        snd_pcm_hw_params_get_period_wakeup(pcm_handle, hwparams, &no_wakeup);
+        if (no_wakeup == 0)
+            pa_log_info("ALSA period wakeups disabled");
+        else
+            pa_log_info("ALSA period wakeups were not disabled");
+    }
+#endif
+
     ss->rate = _ss.rate;
     ss->channels = _ss.channels;
     ss->format = _ss.format;
-- 
1.7.3.2