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

Takashi Iwai
2017-10-24T06:25:16Z

On Sun, 22 Oct 2017 23:40:12 +0200,
Anna-Maria Gleixner 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 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@linutronix.de>
> Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
> Cc: Jaroslav Kysela <perex@perex.cz>
> Cc: Takashi Iwai <tiwai@suse.com>

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

thanks,

Takashi

> Cc: Takashi Sakamoto <o-takashi@sakamocchi.jp>
> Cc: alsa-devel@alsa-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;
> }
>
>
>
>