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

From Takashi Sakamoto <o-takashi@sakamocchi.jp>
Newsgroups linux.kernel
Subject Re: [PATCH 23/25 v3] ALSA/dummy: Replace tasklet with softirq hrtimer
Date 2017-09-06 06:40 +0200
Message-ID <umAi6-4Cl-19@gated-at.bofh.it> (permalink)
References (2 earlier) <ukSMb-3T0-31@gated-at.bofh.it> <ul5q1-4ET-1@gated-at.bofh.it> <umoqB-4Dm-5@gated-at.bofh.it> <umoAj-4Y9-39@gated-at.bofh.it> <umoJX-51S-7@gated-at.bofh.it>
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On Sep 6 2017 01:18, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@linutronix.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@linutronix.de>
> Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
> Cc: Jaroslav Kysela <perex@perex.cz>
> Cc: Takashi Iwai <tiwai@suse.com>
> Cc: Takashi Sakamoto <o-takashi@sakamocchi.jp>
> Cc: alsa-devel@alsa-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@sakamocchi.jp>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.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@sakamocchi.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

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Thread

[PATCH 00/25] hrtimer: Provide softirq context hrtimers Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 07/25] hrtimer: Reduce conditional code (hres_active) Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 05/25] hrtimer: Switch for loop to _ffs() evaluation Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 24/25] net/cdc_ncm: Replace tasklet with softirq hrtimer Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
    Re: [PATCH 24/25] net/cdc_ncm: Replace tasklet with softirq hrtimer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-08-31 15:40 +0200
    Re: [PATCH 24/25] net/cdc_ncm: Replace tasklet with softirq hrtimer Bjørn Mork <bjorn@mork.no> - 2017-08-31 16:00 +0200
      [PATCH 24/25 v2] net/cdc_ncm: Replace tasklet with softirq hrtimer Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-09-05 17:50 +0200
  [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
    Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Iwai <tiwai@suse.de> - 2017-08-31 16:30 +0200
    Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-08-31 16:30 +0200
    Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Iwai <tiwai@suse.de> - 2017-08-31 17:40 +0200
      Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-09-01 12:30 +0200
        Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Iwai <tiwai@suse.de> - 2017-09-01 14:00 +0200
          Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-09-02 03:30 +0200
            Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-09-04 14:50 +0200
            [PATCH 23/25 v2] ALSA/dummy: Replace tasklet with softirq hrtimer Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-09-05 18:00 +0200
              Re: [PATCH 23/25 v2] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Iwai <tiwai@suse.de> - 2017-09-05 18:10 +0200
              Re: [PATCH 23/25 v2] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-09-05 18:10 +0200
                [PATCH 23/25 v3] ALSA/dummy: Replace tasklet with softirq hrtimer Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-09-05 18:20 +0200
                Re: [PATCH 23/25 v3] ALSA/dummy: Replace tasklet with softirq hrtimer Takashi Sakamoto <o-takashi@sakamocchi.jp> - 2017-09-06 06:40 +0200
                Re: [alsa-devel] [PATCH 23/25 v3] ALSA/dummy: Replace tasklet with     softirq hrtimer Takashi Iwai <tiwai@suse.de> - 2017-09-08 10:30 +0200
  [PATCH 22/25] softirq: Remove tasklet_hrtimer Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 21/25] xfrm: Replace hrtimer tasklet with softirq hrtimer Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 06/25] hrtimer: Store running timer in hrtimer_clock_base Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 19/25] can/bcm: Replace hrtimer_tasklet with softirq based  hrtimer Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
    Re: [PATCH 19/25] can/bcm: Replace hrtimer_tasklet with softirq  based hrtimer Thomas Gleixner <tglx@linutronix.de> - 2017-09-01 18:00 +0200
      Re: [PATCH 19/25] can/bcm: Replace hrtimer_tasklet with softirq based  hrtimer Oliver Hartkopp <socketcan@hartkopp.net> - 2017-09-01 19:10 +0200
    Re: [PATCH 19/25] can/bcm: Replace hrtimer_tasklet with softirq based  hrtimer Oliver Hartkopp <socketcan@hartkopp.net> - 2017-09-01 18:00 +0200
    Re: [PATCH 19/25] can/bcm: Replace hrtimer_tasklet with softirq based  hrtimer Oliver Hartkopp <socketcan@hartkopp.net> - 2017-09-02 20:10 +0200
  [PATCH 10/25] hrtimer: Make handling of hrtimer reprogramming and  enqueuing not conditional Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 14/25] hrtimer: Split out code from __hrtimer_get_next_event()  for reuse Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 25/25] usb/gadget/NCM: Replace tasklet with softirq hrtimer Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 03/25] hrtimer: Fix kerneldoc for struct hrtimer_cpu_base Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  [PATCH 09/25] hrtimer: Reduce conditional code (hrtimer_reprogram()) Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:30 +0200
  Re: [PATCH 00/25] hrtimer: Provide softirq context hrtimers Anna-Maria Gleixner <anna-maria@linutronix.de> - 2017-08-31 14:40 +0200

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