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