ASoC: SOF: Use high-priority workqueue for PCM period elapsed

The snd_sof_pcm_period_elapsed function currently schedules work on the
system-wide workqueue. This can lead to potential delays or jitter in
audio processing if the system workqueue is busy with other tasks.

To improve real-time performance and ensure timely processing of PCM
periods, create a dedicated high-priority, unbound workqueue
("sof_pcm_wq") specifically for this purpose.

Update the period elapsed handling to queue work onto this new
workqueue, while maintaining a fallback to the system workqueue if the
dedicated one is not initialized.

Signed-off-by: Yu-Hsuan Hsu <yuhsuan@google.com>

Author: Yu-Hsuan Hsu

sound/soc/sof/core.c

@@ -696,6 +696,12 @@ int snd_sof_device_probe(struct device *dev, struct snd_sof_pdata *plat_data)
 	mutex_init(&sdev->client_event_handler_mutex);
 	mutex_init(&sdev->dsp_fw_boot_mutex);
 
+	/* Create high-priority workqueue for PCM period elapsed work */
+	sdev->pcm_period_wq = alloc_workqueue("sof_pcm_wq", WQ_HIGHPRI | WQ_UNBOUND, 0);
+	if (!sdev->pcm_period_wq) {
+		dev_err(dev, "error: failed to create sof_pcm_wq\n");
+	}
+
 	/* set default timeouts if none provided */
 	if (plat_data->desc->ipc_timeout == 0)
 		sdev->ipc_timeout = TIMEOUT_DEFAULT_IPC_MS;
@@ -797,6 +803,12 @@ int snd_sof_device_remove(struct device *dev)
 	/* release firmware */
 	snd_sof_fw_unload(sdev);
 
+	/* Destroy the PCM workqueue */
+	if (sdev->pcm_period_wq) {
+		destroy_workqueue(sdev->pcm_period_wq);
+		sdev->pcm_period_wq = NULL;
+	}
+
 	return 0;
 }
 EXPORT_SYMBOL(snd_sof_device_remove);

sound/soc/sof/pcm.c

@@ -45,6 +45,7 @@ void snd_sof_pcm_period_elapsed(struct snd_pcm_substream *substream)
 	struct snd_soc_pcm_runtime *rtd = snd_soc_substream_to_rtd(substream);
 	struct snd_soc_component *component =
 		snd_soc_rtdcom_lookup(rtd, SOF_AUDIO_PCM_DRV_NAME);
+	struct snd_sof_dev *sdev = snd_soc_component_get_drvdata(component);
 	struct snd_sof_pcm *spcm;
 
 	spcm = snd_sof_find_spcm_dai(component, rtd);
@@ -62,7 +63,12 @@ void snd_sof_pcm_period_elapsed(struct snd_pcm_substream *substream)
 	 * To avoid sending IPC before the previous IPC is handled, we
 	 * schedule delayed work here to call the snd_pcm_period_elapsed().
 	 */
-	schedule_work(&spcm->stream[substream->stream].period_elapsed_work);
+	if (sdev->pcm_period_wq) {
+		queue_work(sdev->pcm_period_wq, &spcm->stream[substream->stream].period_elapsed_work);
+	} else {
+		// Fallback to system workqueue
+		schedule_work(&spcm->stream[substream->stream].period_elapsed_work);
+	}
 }
 EXPORT_SYMBOL(snd_sof_pcm_period_elapsed);
 

sound/soc/sof/sof-priv.h

@@ -701,6 +701,8 @@ struct snd_sof_dev {
 	/* used to store the FW filename and path passed from userspace for DSP ops testing */
 	struct sof_loadable_file_profile test_profile;
 
+	struct workqueue_struct *pcm_period_wq; /* WQ for PCM period elapsed */
+
 	void *private;			/* core does not touch this */
 };