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

Anna-Maria Gleixner
2017-10-22T21:43:36Z

[-- Attachment #1: ALSAdummy_Replace_tasklet_with_softirq_hrtimer.patch --]
[-- Type: text/plain, Size: 4008 bytes --]

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>
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;
}