linux-kernel - Re: [PATCH v2 34/37] ALSA/dummy: Replace tasklet with softirq hrtimer

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Message-ID: <s5hzi8hqczj.wl-tiwai@suse.de>
Date:   Tue, 24 Oct 2017 08:25:04 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Anna-Maria Gleixner" <anna-maria@...utronix.de>
Cc:     "LKML" <linux-kernel@...r.kernel.org>,
        <alsa-devel@...a-project.org>, <keescook@...omium.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "John Stultz" <john.stultz@...aro.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Christoph Hellwig" <hch@....de>,
        "Jaroslav Kysela" <perex@...ex.cz>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Takashi Sakamoto" <o-takashi@...amocchi.jp>
Subject: Re: [PATCH v2 34/37] ALSA/dummy: Replace tasklet with softirq hrtimer

On Sun, 22 Oct 2017 23:40:12 +0200,
Anna-Maria Gleixner 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 HRTIMER_MODE_SOFT mode invokes the timer
> callback in softirq context as well which renders the tasklet useless.
> 
> [o-takashi: avoid stall due to a call of hrtimer_cancel() on a callback
>             of hrtimer]
> 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>

Feel free to take my ack:
  Reviewed-by: Takashi Iwai <tiwai@...e.de>


thanks,

Takashi

> Cc: Takashi Sakamoto <o-takashi@...amocchi.jp>
> Cc: alsa-devel@...a-project.org
> Link: http://lkml.kernel.org/r/20170905161820.jtysvxtfleunbbmf@breakpoint.cc
> 
> ---
> 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 |   27 ++++++++++++---------------
>  1 file changed, 12 insertions(+), 15 deletions(-)
> 
> --- 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_hrtime
>  	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;
>  }
> @@ -404,7 +403,7 @@ static int dummy_hrtimer_start(struct sn
>  	struct dummy_hrtimer_pcm *dpcm = substream->runtime->private_data;
>  
>  	dpcm->base_time = hrtimer_cb_get_time(&dpcm->timer);
> -	hrtimer_start(&dpcm->timer, dpcm->period_time, HRTIMER_MODE_REL);
> +	hrtimer_start(&dpcm->timer, dpcm->period_time, HRTIMER_MODE_REL_SOFT);
>  	atomic_set(&dpcm->running, 1);
>  	return 0;
>  }
> @@ -414,14 +413,14 @@ static int dummy_hrtimer_stop(struct snd
>  	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 s
>  	if (!dpcm)
>  		return -ENOMEM;
>  	substream->runtime->private_data = dpcm;
> -	hrtimer_init(&dpcm->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	hrtimer_init(&dpcm->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
>  	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;
>  }
>  
> 
> 
>