ALSA: pcm_lib - optimize wake_up() calls for PCM I/O

As noted by pl bossart <bossart.nospam@gmail.com>, the PCM I/O routines
(snd_pcm_lib_write1, snd_pcm_lib_read1) should block wake_up() calls
until all samples are not processed.
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

include/sound/pcm.h

@@ -311,6 +311,7 @@ struct snd_pcm_runtime {
 	struct snd_pcm_mmap_control *control;
 
 	/* -- locking / scheduling -- */
+	unsigned int nowake: 1;		/* no wakeup (data-copy in progress) */
 	wait_queue_head_t sleep;
 	struct fasync_struct *fasync;
 
@@ -839,6 +840,8 @@ void snd_pcm_set_sync(struct snd_pcm_substream *substream);
 int snd_pcm_lib_interleave_len(struct snd_pcm_substream *substream);
 int snd_pcm_lib_ioctl(struct snd_pcm_substream *substream,
 		      unsigned int cmd, void *arg);                      
+int snd_pcm_update_state(struct snd_pcm_substream *substream,
+			 struct snd_pcm_runtime *runtime);
 int snd_pcm_update_hw_ptr(struct snd_pcm_substream *substream);
 int snd_pcm_playback_xrun_check(struct snd_pcm_substream *substream);
 int snd_pcm_capture_xrun_check(struct snd_pcm_substream *substream);

sound/core/pcm_lib.c

@@ -263,7 +263,7 @@ static void xrun_log_show(struct snd_pcm_substream *substream)
 
 #endif
 
-static int snd_pcm_update_hw_ptr_post(struct snd_pcm_substream *substream,
+int snd_pcm_update_state(struct snd_pcm_substream *substream,
 			 struct snd_pcm_runtime *runtime)
 {
 	snd_pcm_uframes_t avail;
@@ -285,7 +285,7 @@ static int snd_pcm_update_hw_ptr_post(struct snd_pcm_substream *substream,
 			return -EPIPE;
 		}
 	}
-	if (avail >= runtime->control->avail_min)
+	if (!runtime->nowake && avail >= runtime->control->avail_min)
 		wake_up(&runtime->sleep);
 	return 0;
 }
@@ -441,7 +441,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
 	if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE)
 		snd_pcm_gettime(runtime, (struct timespec *)&runtime->status->tstamp);
 
-	return snd_pcm_update_hw_ptr_post(substream, runtime);
+	return snd_pcm_update_state(substream, runtime);
 }
 
 /* CAUTION: call it with irq disabled */
@@ -1792,6 +1792,7 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream,
 		goto _end_unlock;
 	}
 
+	runtime->nowake = 1;
 	while (size > 0) {
 		snd_pcm_uframes_t frames, appl_ptr, appl_ofs;
 		snd_pcm_uframes_t avail;
@@ -1813,15 +1814,17 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream,
 		if (frames > cont)
 			frames = cont;
 		if (snd_BUG_ON(!frames)) {
+			runtime->nowake = 0;
 			snd_pcm_stream_unlock_irq(substream);
 			return -EINVAL;
 		}
 		appl_ptr = runtime->control->appl_ptr;
 		appl_ofs = appl_ptr % runtime->buffer_size;
 		snd_pcm_stream_unlock_irq(substream);
-		if ((err = transfer(substream, appl_ofs, data, offset, frames)) < 0)
-			goto _end;
+		err = transfer(substream, appl_ofs, data, offset, frames);
 		snd_pcm_stream_lock_irq(substream);
+		if (err < 0)
+			goto _end_unlock;
 		switch (runtime->status->state) {
 		case SNDRV_PCM_STATE_XRUN:
 			err = -EPIPE;
@@ -1850,8 +1853,10 @@ static snd_pcm_sframes_t snd_pcm_lib_write1(struct snd_pcm_substream *substream,
 		}
 	}
  _end_unlock:
+	runtime->nowake = 0;
+	if (xfer > 0 && err >= 0)
+		snd_pcm_update_state(substream, runtime);
 	snd_pcm_stream_unlock_irq(substream);
- _end:
 	return xfer > 0 ? (snd_pcm_sframes_t)xfer : err;
 }
 
@@ -2009,6 +2014,7 @@ static snd_pcm_sframes_t snd_pcm_lib_read1(struct snd_pcm_substream *substream,
 		goto _end_unlock;
 	}
 
+	runtime->nowake = 1;
 	while (size > 0) {
 		snd_pcm_uframes_t frames, appl_ptr, appl_ofs;
 		snd_pcm_uframes_t avail;
@@ -2037,15 +2043,17 @@ static snd_pcm_sframes_t snd_pcm_lib_read1(struct snd_pcm_substream *substream,
 		if (frames > cont)
 			frames = cont;
 		if (snd_BUG_ON(!frames)) {
+			runtime->nowake = 0;
 			snd_pcm_stream_unlock_irq(substream);
 			return -EINVAL;
 		}
 		appl_ptr = runtime->control->appl_ptr;
 		appl_ofs = appl_ptr % runtime->buffer_size;
 		snd_pcm_stream_unlock_irq(substream);
-		if ((err = transfer(substream, appl_ofs, data, offset, frames)) < 0)
-			goto _end;
+		err = transfer(substream, appl_ofs, data, offset, frames);
 		snd_pcm_stream_lock_irq(substream);
+		if (err < 0)
+			goto _end_unlock;
 		switch (runtime->status->state) {
 		case SNDRV_PCM_STATE_XRUN:
 			err = -EPIPE;
@@ -2068,8 +2076,10 @@ static snd_pcm_sframes_t snd_pcm_lib_read1(struct snd_pcm_substream *substream,
 		xfer += frames;
 	}
  _end_unlock:
+	runtime->nowake = 0;
+	if (xfer > 0 && err >= 0)
+		snd_pcm_update_state(substream, runtime);
 	snd_pcm_stream_unlock_irq(substream);
- _end:
 	return xfer > 0 ? (snd_pcm_sframes_t)xfer : err;
 }
 

sound/core/pcm_native.c

@@ -516,6 +516,7 @@ static int snd_pcm_sw_params(struct snd_pcm_substream *substream,
 			     struct snd_pcm_sw_params *params)
 {
 	struct snd_pcm_runtime *runtime;
+	int err;
 
 	if (PCM_RUNTIME_CHECK(substream))
 		return -ENXIO;
@@ -540,6 +541,7 @@ static int snd_pcm_sw_params(struct snd_pcm_substream *substream,
 		if (params->silence_threshold > runtime->buffer_size)
 			return -EINVAL;
 	}
+	err = 0;
 	snd_pcm_stream_lock_irq(substream);
 	runtime->tstamp_mode = params->tstamp_mode;
 	runtime->period_step = params->period_step;
@@ -553,10 +555,10 @@ static int snd_pcm_sw_params(struct snd_pcm_substream *substream,
 		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
 		    runtime->silence_size > 0)
 			snd_pcm_playback_silence(substream, ULONG_MAX);
-		wake_up(&runtime->sleep);
+		err = snd_pcm_update_state(substream, runtime);
 	}
 	snd_pcm_stream_unlock_irq(substream);
-	return 0;
+	return err;
 }
 
 static int snd_pcm_sw_params_user(struct snd_pcm_substream *substream,