Re: [alsa-devel] [PATCH] ASoC: tlv320dac33: Remove deprecated create_singlethread_workqueue

[Peter Ujfalusi]

On 08/30/16 21:27, Bhaktipriya Shridhar wrote:
> The workqueue "dac33_wq" queues a single work item &dac33->work and hence
> doesn't require ordering. Also, it is not being used on a memory reclaim
> path. Hence, it has been converted to use system_wq.
>
> The work item has been flushed in dac33_soc_remove to ensure that
> there are no pending tasks while disconnecting the driver.

The reason why dac33 had it's own wq is that it is absolutely time critical
that the work is not going to be delayed by the scheduling needs with the
system_wq. If the work execution is delayed, we could run out of time in FIFO
mode, which can cause the chip to hang do to FIFO underrun.

Unfortunately I'm no longer able to test the dac33 as I don't have the HW any
more.

If you are 100% percent sure that this is not going to delay the work, then
I'm OK with the change, but I have used the dedicated queue at the time,
because the system_wq given unpredictable latencies.

> The workqueue "post_msg_wq" queues a single work item
> &drv->ipc_post_msg_wq and hence doesn't require ordering. Also, it is
> not being used on a memory reclaim path. Hence, it has been converted to
> use system_wq.
> 
> The work item has been flushed in sst_context_cleanup to ensure that
> there are no pending tasks while disconnecting the driver.
> 
> System workqueues have been able to handle high level of concurrency
> for a long time now and hence it's not required to have a singlethreaded
> workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
> created with create_singlethread_workqueue(), system_wq allows multiple
> work items to overlap executions even on the same CPU; however, a
> per-cpu workqueue doesn't have any CPU locality or global ordering
> guarantee unless the target CPU is explicitly specified and thus the
> increase of local concurrency shouldn't make any difference.
> 
> Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@xxxxxxxxx>
> ---
>  sound/soc/codecs/tlv320dac33.c | 17 ++++-------------
>  sound/soc/intel/atom/sst/sst.c | 14 +++++---------

two separate patch?

>  2 files changed, 9 insertions(+), 22 deletions(-)
> 
> diff --git a/sound/soc/codecs/tlv320dac33.c b/sound/soc/codecs/tlv320dac33.c
> index f7a6ce7..6822ac1 100644
> --- a/sound/soc/codecs/tlv320dac33.c
> +++ b/sound/soc/codecs/tlv320dac33.c
> @@ -90,7 +90,6 @@ static const char *dac33_supply_names[DAC33_NUM_SUPPLIES] = {
> 
>  struct tlv320dac33_priv {
>  	struct mutex mutex;
> -	struct workqueue_struct *dac33_wq;
>  	struct work_struct work;
>  	struct snd_soc_codec *codec;
>  	struct regulator_bulk_data supplies[DAC33_NUM_SUPPLIES];
> @@ -771,7 +770,7 @@ static irqreturn_t dac33_interrupt_handler(int irq, void *dev)
> 
>  	/* Do not schedule the workqueue in Mode7 */
>  	if (dac33->fifo_mode != DAC33_FIFO_MODE7)
> -		queue_work(dac33->dac33_wq, &dac33->work);
> +		schedule_work(&dac33->work);
> 
>  	return IRQ_HANDLED;
>  }
> @@ -1127,7 +1126,7 @@ static int dac33_pcm_trigger(struct snd_pcm_substream *substream, int cmd,
>  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>  		if (dac33->fifo_mode) {
>  			dac33->state = DAC33_PREFILL;
> -			queue_work(dac33->dac33_wq, &dac33->work);
> +			schedule_work(&dac33->work);
>  		}
>  		break;
>  	case SNDRV_PCM_TRIGGER_STOP:
> @@ -1135,7 +1134,7 @@ static int dac33_pcm_trigger(struct snd_pcm_substream *substream, int cmd,
>  	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
>  		if (dac33->fifo_mode) {
>  			dac33->state = DAC33_FLUSH;
> -			queue_work(dac33->dac33_wq, &dac33->work);
> +			schedule_work(&dac33->work);
>  		}
>  		break;
>  	default:
> @@ -1410,14 +1409,6 @@ static int dac33_soc_probe(struct snd_soc_codec *codec)
>  			dac33->irq = -1;
>  		}
>  		if (dac33->irq != -1) {
> -			/* Setup work queue */
> -			dac33->dac33_wq =
> -				create_singlethread_workqueue("tlv320dac33");
> -			if (dac33->dac33_wq == NULL) {
> -				free_irq(dac33->irq, codec);
> -				return -ENOMEM;
> -			}
> -
>  			INIT_WORK(&dac33->work, dac33_work);
>  		}
>  	}
> @@ -1437,7 +1428,7 @@ static int dac33_soc_remove(struct snd_soc_codec *codec)
> 
>  	if (dac33->irq >= 0) {
>  		free_irq(dac33->irq, dac33->codec);
> -		destroy_workqueue(dac33->dac33_wq);
> +		flush_work(&dac33->work);
>  	}
>  	return 0;
>  }
> diff --git a/sound/soc/intel/atom/sst/sst.c b/sound/soc/intel/atom/sst/sst.c
> index a4b458e..8cfd0cf 100644
> --- a/sound/soc/intel/atom/sst/sst.c
> +++ b/sound/soc/intel/atom/sst/sst.c
> @@ -76,7 +76,7 @@ static irqreturn_t intel_sst_interrupt_mrfld(int irq, void *context)
>  		spin_unlock(&drv->ipc_spin_lock);
> 
>  		/* we can send more messages to DSP so trigger work */
> -		queue_work(drv->post_msg_wq, &drv->ipc_post_msg_wq);
> +		schedule_work(&drv->ipc_post_msg_wq);
>  		retval = IRQ_HANDLED;
>  	}
> 
> @@ -212,10 +212,6 @@ static int sst_workqueue_init(struct intel_sst_drv *ctx)
>  	INIT_WORK(&ctx->ipc_post_msg_wq, sst_process_pending_msg);
>  	init_waitqueue_head(&ctx->wait_queue);
> 
> -	ctx->post_msg_wq =
> -		create_singlethread_workqueue("sst_post_msg_wq");
> -	if (!ctx->post_msg_wq)
> -		return -EBUSY;
>  	return 0;
>  }
> 
> @@ -318,7 +314,6 @@ int sst_context_init(struct intel_sst_drv *ctx)
>  	return 0;
> 
>  do_free_mem:
> -	destroy_workqueue(ctx->post_msg_wq);
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(sst_context_init);
> @@ -330,7 +325,7 @@ void sst_context_cleanup(struct intel_sst_drv *ctx)
>  	sst_unregister(ctx->dev);
>  	sst_set_fw_state_locked(ctx, SST_SHUTDOWN);
>  	flush_scheduled_work();
> -	destroy_workqueue(ctx->post_msg_wq);
> +	flush_work(&ctx->ipc_post_msg_wq);
>  	pm_qos_remove_request(ctx->qos);
>  	kfree(ctx->fw_sg_list.src);
>  	kfree(ctx->fw_sg_list.dst);
> @@ -414,7 +409,7 @@ static int intel_sst_runtime_suspend(struct device *dev)
>  	sst_set_fw_state_locked(ctx, SST_RESET);
> 
>  	synchronize_irq(ctx->irq_num);
> -	flush_workqueue(ctx->post_msg_wq);
> +	flush_work(&ctx->ipc_post_msg_wq);
> 
>  	ctx->ops->reset(ctx);
>  	/* save the shim registers because PMC doesn't save state */
> @@ -445,8 +440,9 @@ static int intel_sst_suspend(struct device *dev)
>  			return -EBUSY;
>  		}
>  	}
> +
>  	synchronize_irq(ctx->irq_num);
> -	flush_workqueue(ctx->post_msg_wq);
> +	flush_work(ctx->ipc_post_msg_wq);
> 
>  	/* Move the SST state to Reset */
>  	sst_set_fw_state_locked(ctx, SST_RESET);
> --
> 2.1.4
> 
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