On Wed, 15 May 2019 08:26:37 +0200,
<vanitha.channaiah@xxxxxxxxxxxx> wrote:
>
> From: Vanitha Channaiah <vanitha.channaiah@xxxxxxxxxxxx>
>
> This Fix was analyzed for below usecase :
>
> alsa configuration:
> pcm.line_in {
> type dsnoop
> ipc_key INT
> slave {
> pcm hardware
> channels 2
> period_time 8000
> rate 48000
> format S16_LE
> }
> bindings {
> 0 0
> 1 1
> }
> }
> pcm.hardware {
> type hw
> card "gmd-card"
> device 0
> subdevice 0
> channels 2
> period_time 2000
> rate 48000
> format S16_LE
> }
>
> command:
> $arecord -v -D line_in -r 48000 -c 2 -f S16_LE recordfile.wav
> Direct Snoop PCM
> Its setup is:
> stream : CAPTURE
> access : RW_INTERLEAVED
> format : S16_LE
> subformat : STD
> channels : 2
> rate : 48000
> exact rate : 48000 (48000/1)
> msbits : 16
> buffer_size : 1536
> period_size : 384
> period_time : 8000
> tstamp_mode : NONE
> tstamp_type : MONOTONIC
> period_step : 1
> avail_min : 384
> period_event : 0
> start_threshold : 1
> stop_threshold : 1536
> silence_threshold: 0
> silence_size : 0
> boundary : huge value
> Hardware PCM card 3 'gmd-card' device 0 subdevice 0
> Its setup is:
> stream : CAPTURE
> access : MMAP_INTERLEAVED
> format : S16_LE
> subformat : STD
> channels : 2
> rate : 48000
> exact rate : 48000 (48000/1)
> msbits : 16
> buffer_size : 1536
> period_size : 96
> period_time : 2000
> tstamp_mode : ENABLE
> tstamp_type : MONOTONIC
> period_step : 1
> avail_min : 96
> period_event : 0
> start_threshold : 1
> stop_threshold : huge value
> silence_threshold: 0
> silence_size : 0
> boundary : huge value
> appl_ptr : 0
> hw_ptr : 576
>
> Here, there are no other plugins apart from Dsnoop.
>
> Issue: After partial read of unaligned frames(not one period frames),
> snd_pcm_wait() would block for the pcm->avail_min which would result in
> blocking for longer periods i.e more than one period as specified by
> pcm->avail_min
>
> For e.g.:
> Slave period size = 0x60
> Client period-size=0x180
> No. of Ticks = 4
> pcm->avail_min = one period size = 0x180
>
> Issue:
> - During the start of streaming, the position of slave hw_ptr returned
> from the driver is 0x20.
> - avail is 0x20
> - hw_ptr is calculated by new_slave_hw_ptr - old_slave_hw_ptr i.e.
> 0x20 - 0 = 0x20
> - hw_ptr updated to 0x20
> - avail is 0x20
> - app_ptr updated to 0x20
> - Now, avail = 0
> - snd_pcm_wait() waits till avail=0x180 because pcm->avail_min = 0x180
> - After 4 snd_pcm_elapsed(), slave_hw_ptr = 0x180
> - Since app_ptr has updated with 0x20, avail becomes 0x160
> There is a shortage of 0x20 frames and hence snd_pcm_wait()
> goes back to wait again.
> - Now, snd_pcm_wait is locked.
> - After another 4 snd_pcm_elapsed() slave_hw_ptr = 0x300
> - avail = 0x2e0
> - snd_pcm_wait() unlocks.
> So, here snd_pcm_wait() is locked for more than 1 period(exactly 2 periods)
>
> Also, this issue can be seen without dsnoop plugin, when HW reports unaligned hw_ptr
> For e.g.
> period size = 0x60
> pcm->avail_min = 0x60
> - During the start of streaming, the position of slave hw_ptr returned
> from the driver is 0x20.
> - hw_ptr is calculated by new_slave_hw_ptr - old_slave_hw_ptr i.e.
> 0x20 - 0 = 0x20
> - hw_ptr updated to 0x20
> - avail is 0x20
> - app_ptr updated to 0x20
> - Now, avail = 0
> - snd_pcm_wait() waits till avail=0x60 because pcm->avail_min=0x60
> - After 1 snd_pcm_elapsed(), slave_hw_ptr = 0x60
> - Since app_ptr has updated with 0x20, avail becomes 0x40
> There is a shortage of 0x20 frames and hence snd_pcm_wait()
> goes back to wait again.
> - Now, snd_pcm_wait is locked.
> - After another 1 snd_pcm_elapsed(), slave_hw_ptr = 0x120
> - avail = 0xe0
> - snd_pcm_wait() unlocks.
> So, here snd_pcm_wait() is locked for more than 1 period (exactly 2 periods)
>
> Fix: After reading unaligned frames(not one period frames),
> set the pcm->avail_min to the needed_avail_slave_min frames
> so that snd_pcm_wait() blocks till needed_avail_slave_min available
> Once needed_avail_slave_min frames are read, set back the original
> pcm->avail_min
>
> For ex:
> Slave period size = 0x60
> Client period-size=0x180
> No. of Ticks = 4
> pcm->avail_min = one period size = 0x180
>
> Fix:
> - During the start of streaming, the position of slave_hw_ptr returned
> from the driver is 0x20.
> - hw_ptr is calculated by new_slave_hw_ptr - old_slave_hw_ptr
> i.e. 0x20 - 0 = 0x20
> - hw_ptr updated to 0x20
> - avail is 0x20
> - app_ptr updated to 0x20
> - Now, avail = 0
> - calculate needed_avail_slave_min = 0x160
> - update the needed_avail_slave_min to pcm->avail_min
> i.e. pcm->avail_min = 0x160
> - snd_pcm_wait() waits till avail=0x160
> - After 4 snd_pcm_elapsed(), slave_hw_ptr = 0x180
> - snd_pcm_wait() unlocks.
> - Once needed_avail_slave_min frames are read, set back the
> original pcm->avail_min to 0x180
> So, here snd_pcm_wait() is locked for 1 period only.
>
> Signed-off-by: Vanitha Channaiah <vanitha.channaiah@xxxxxxxxxxxx>
> ---
> src/pcm/pcm.c | 21 +++++++++++++++++++++
> src/pcm/pcm_local.h | 2 ++
> 2 files changed, 23 insertions(+)
>
> diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
> index f0db545..f361eb1 100644
> --- a/src/pcm/pcm.c
> +++ b/src/pcm/pcm.c
> @@ -973,6 +973,7 @@ int snd_pcm_sw_params(snd_pcm_t *pcm, snd_pcm_sw_params_t *params)
> __snd_pcm_unlock(pcm);
> return err;
> }
> + pcm->original_avail_min = pcm->avail_min;
> __snd_pcm_unlock(pcm);
> return 0;
> }
> @@ -7267,6 +7268,17 @@ void snd_pcm_areas_from_bufs(snd_pcm_t *pcm, snd_pcm_channel_area_t *areas,
> snd_pcm_unlock(pcm);
> }
>
> +static void snd_pcm_set_avail_min(snd_pcm_t *pcm, snd_pcm_uframes_t avail)
> +{
> + if (avail != pcm->avail_min) {
> + snd_pcm_sw_params_t swparams;
> +
> + snd_pcm_sw_params_current(pcm, &swparams);
> + swparams.avail_min = avail;
> + _snd_pcm_sw_params_internal(pcm, &swparams);
> + }
> +}
> +
> snd_pcm_sframes_t snd_pcm_read_areas(snd_pcm_t *pcm, const snd_pcm_channel_area_t *areas,
> snd_pcm_uframes_t offset, snd_pcm_uframes_t size,
> snd_pcm_xfer_areas_func_t func)
> @@ -7274,6 +7286,7 @@ snd_pcm_sframes_t snd_pcm_read_areas(snd_pcm_t *pcm, const snd_pcm_channel_area_
> snd_pcm_uframes_t xfer = 0;
> snd_pcm_sframes_t err = 0;
> snd_pcm_state_t state;
> + snd_pcm_uframes_t needed_slave_avail_min = 0;
>
> if (size == 0)
> return 0;
> @@ -7332,6 +7345,14 @@ snd_pcm_sframes_t snd_pcm_read_areas(snd_pcm_t *pcm, const snd_pcm_channel_area_
> if (err < 0)
> break;
> frames = err;
> + pcm->unaligned_frames += frames;
> + pcm->unaligned_frames %= pcm->period_size;
> + if (pcm->unaligned_frames) {
> + needed_slave_avail_min = pcm->period_size - pcm->unaligned_frames;
> + snd_pcm_set_avail_min(pcm, needed_slave_avail_min);
> + } else {
> + snd_pcm_set_avail_min(pcm, pcm->original_avail_min);
> + }
> offset += frames;
> size -= frames;
> xfer += frames;
> diff --git a/src/pcm/pcm_local.h b/src/pcm/pcm_local.h
> index e103f72..3fdffb4 100644
> --- a/src/pcm/pcm_local.h
> +++ b/src/pcm/pcm_local.h
> @@ -210,6 +210,8 @@ struct _snd_pcm {
> snd_pcm_tstamp_type_t tstamp_type; /* timestamp type */
> unsigned int period_step;
> snd_pcm_uframes_t avail_min; /* min avail frames for wakeup */
> + snd_pcm_uframes_t unaligned_frames;
> + snd_pcm_uframes_t original_avail_min;
> int period_event;
> snd_pcm_uframes_t start_threshold;
> snd_pcm_uframes_t stop_threshold;
Can we avoid adding such a hack in the core code?
Basically the issue is very specific to direct-plugins, so this sort
of workaround should be implemented locally there instead. I guess we
can do similar tricks by overriding the calls in the callbacks.
thanks,
Takashi
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