linux-kernel - Re: [PATCH 23/25 v3] ALSA/dummy: Replace tasklet with softirq hrtimer

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Message-ID: <4d532df1-1581-f390-322d-39de5595d26f@sakamocchi.jp>
Date:   Wed, 6 Sep 2017 13:30:03 +0900
From:   Takashi Sakamoto <o-takashi@...amocchi.jp>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     alsa-devel@...a-project.org, keescook@...omium.org,
        Takashi Iwai <tiwai@...e.de>, linux-kernel@...r.kernel.org,
        peterz@...radead.org, mingo@...hat.com, john.stultz@...aro.org,
        tglx@...utronix.de, anna-maria@...utronix.de, hch@....de
Subject: Re: [PATCH 23/25 v3] ALSA/dummy: Replace tasklet with softirq hrtimer

On Sep 6 2017 01:18, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The tasklet is used to defer the execution of snd_pcm_period_elapsed() to
> the softirq context. Using the CLOCK_MONOTONIC_SOFT base invokes the timer
> callback in softirq context as well which renders the tasklet useless.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> Cc: Jaroslav Kysela <perex@...ex.cz>
> Cc: Takashi Iwai <tiwai@...e.com>
> Cc: Takashi Sakamoto <o-takashi@...amocchi.jp>
> Cc: alsa-devel@...a-project.org
> [o-takashi: avoid stall due to a call of hrtimer_cancel() on a callback
>              of hrtimer]
> Signed-off-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> On 2017-09-06 01:05:43 [+0900], Takashi Sakamoto wrote:
>> As Iwai-san mentioned, in this function, .trigger can be called in two
>> cases; XRUN occurs and draining is done. Thus, let you change the comment as
>> 'In cases of XRUN and draining, this calls .trigger to stop PCM substream.'.
>> I'm sorry to trouble you.
>>
>> snd_pcm_period_elapsed()
>> ->snd_pcm_update_hw_ptr0()
>>    ->snd_pcm_update_state()
>>      ->snd_pcm_drain_done()
>>        ...
>>        ->.trigger(TRIGGER_STOP)
>>      ->xrun()
>>        ->snd_pcm_stop()
>>          ...
>>          ->.trigger(TRIGGER_STOP)
>>
> 
> I think you asked me just to update the comment. Did I do it right?
> 
> v2…v3: updated the comment as per Takashi Sakamoto's suggestion.
> v1…v2: merged Takashi Sakamoto fixup of the original patch into v2.
> 
>   sound/drivers/dummy.c | 25 +++++++++++--------------
>   1 file changed, 11 insertions(+), 14 deletions(-)

This Looks good to me. I did quick test and confirmed that it brings no 
stalls.

Tested-by: Takashi Sakamoto <o-takashi@...amocchi.jp>

> diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
> index dd5ed037adf2..cdd851286f92 100644
> --- a/sound/drivers/dummy.c
> +++ b/sound/drivers/dummy.c
> @@ -376,17 +376,9 @@ struct dummy_hrtimer_pcm {
>   	ktime_t period_time;
>   	atomic_t running;
>   	struct hrtimer timer;
> -	struct tasklet_struct tasklet;
>   	struct snd_pcm_substream *substream;
>   };
>   
> -static void dummy_hrtimer_pcm_elapsed(unsigned long priv)
> -{
> -	struct dummy_hrtimer_pcm *dpcm = (struct dummy_hrtimer_pcm *)priv;
> -	if (atomic_read(&dpcm->running))
> -		snd_pcm_period_elapsed(dpcm->substream);
> -}
> -
>   static enum hrtimer_restart dummy_hrtimer_callback(struct hrtimer *timer)
>   {
>   	struct dummy_hrtimer_pcm *dpcm;
> @@ -394,7 +386,14 @@ static enum hrtimer_restart dummy_hrtimer_callback(struct hrtimer *timer)
>   	dpcm = container_of(timer, struct dummy_hrtimer_pcm, timer);
>   	if (!atomic_read(&dpcm->running))
>   		return HRTIMER_NORESTART;
> -	tasklet_schedule(&dpcm->tasklet);
> +	/*
> +	 * In cases of XRUN and draining, this calls .trigger to stop PCM
> +	 * substream.
> +	 */
> +	snd_pcm_period_elapsed(dpcm->substream);
> +	if (!atomic_read(&dpcm->running))
> +		return HRTIMER_NORESTART;
> +
>   	hrtimer_forward_now(timer, dpcm->period_time);
>   	return HRTIMER_RESTART;
>   }
> @@ -414,14 +413,14 @@ static int dummy_hrtimer_stop(struct snd_pcm_substream *substream)
>   	struct dummy_hrtimer_pcm *dpcm = substream->runtime->private_data;
>   
>   	atomic_set(&dpcm->running, 0);
> -	hrtimer_cancel(&dpcm->timer);
> +	if (!hrtimer_callback_running(&dpcm->timer))
> +		hrtimer_cancel(&dpcm->timer);
>   	return 0;
>   }
>   
>   static inline void dummy_hrtimer_sync(struct dummy_hrtimer_pcm *dpcm)
>   {
>   	hrtimer_cancel(&dpcm->timer);
> -	tasklet_kill(&dpcm->tasklet);
>   }
>   
>   static snd_pcm_uframes_t
> @@ -466,12 +465,10 @@ static int dummy_hrtimer_create(struct snd_pcm_substream *substream)
>   	if (!dpcm)
>   		return -ENOMEM;
>   	substream->runtime->private_data = dpcm;
> -	hrtimer_init(&dpcm->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	hrtimer_init(&dpcm->timer, CLOCK_MONOTONIC_SOFT, HRTIMER_MODE_REL);
>   	dpcm->timer.function = dummy_hrtimer_callback;
>   	dpcm->substream = substream;
>   	atomic_set(&dpcm->running, 0);
> -	tasklet_init(&dpcm->tasklet, dummy_hrtimer_pcm_elapsed,
> -		     (unsigned long)dpcm);
>   	return 0;
>   }


Thanks

Takashi Sakamoto