starting from kernel 5.10.x latency test fails systematically on multiple platforms

Wed Nov 23 08:51:37 CET 2022

alsa-project/alsa-lib issue #285 was edited from bondagit:

If I try the latency test application ([test/latency.c](https://github.com/alsa-project/alsa-lib/blob/master/test/latency.c)) using a **Linux Kernel 5.9.x** with alsa-lib v1.2.4 on the following audio card:
_PCH [HDA Intel PCH], device 1: ALC269VC Analog [ALC269VC Analog]_ (for example)
I get the following result:

```
sudo ./latency -C hw:1 -P hw:1 -f S16_LE -r 48000 -c 2  -s 10 -m 128 -M 128 
Scheduler set to Round Robin with priority 99...
Playback device is hw:1
Capture device is hw:1
Parameters are 48000Hz, S16_LE, 2 channels, non-blocking mode
Poll mode: no
Loop limit is 480000 frames, minimum latency = 128, maximum latency = 128
Hardware PCM card 1 'HDA Intel PCH' device 0 subdevice 0
Its setup is:
  stream       : PLAYBACK
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 2
  rate         : 48000
  exact rate   : 48000 (48000/1)
  msbits       : 16
  buffer_size  : 128
  period_size  : 64
  period_time  : 1333
  tstamp_mode  : NONE
  tstamp_type  : MONOTONIC
  period_step  : 1
  avail_min    : 64
  period_event : 0
  start_threshold  : 2147483647
  stop_threshold   : 128
  silence_threshold: 0
  silence_size : 0
  boundary     : 4611686018427387904
  appl_ptr     : 0
  hw_ptr       : 0
Hardware PCM card 1 'HDA Intel PCH' device 0 subdevice 0
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  : 128
  period_size  : 64
  period_time  : 1333
  tstamp_mode  : NONE
  tstamp_type  : MONOTONIC
  period_step  : 1
  avail_min    : 64
  period_event : 0
  start_threshold  : 2147483647
  stop_threshold   : 128
  silence_threshold: 0
  silence_size : 0
  boundary     : 4611686018427387904
  appl_ptr     : 0
  hw_ptr       : 0
Trying latency 128 frames, 2666.667us, 2.666667ms (375.0000Hz)
Success
Playback:
*** frames = 480128 ***
  state       : RUNNING
  trigger_time: 1907393.672215
  tstamp      : 0.000000
  delay       : 80
  avail       : 48
  avail_max   : 64
Capture:
*** frames = 480000 ***
  state       : RUNNING
  trigger_time: 1907393.672215
  tstamp      : 0.000000
  delay       : 0
  avail       : 0
  avail_max   : 16
Maximum read: 16 frames
Maximum read latency: 333.333us, 0.333333ms (3000.0000Hz)
Hardware sync
Playback time = 1907393.672215, Record time = 1907393.672215, diff = 0
```

The tests succeeded and final state is **RUNNING**

If I try the same tests on the same audio device and distribution but with a **Linux Kernel >= 5.10.x** it fails systematically and I get:

```
sudo ./lantency -C hw:1 -P hw:1 -f S16_LE -r 48000 -c 2  -s 10 -m 128 -M 128 
Scheduler set to Round Robin with priority 99...
Playback device is hw:0
Capture device is hw:0
Parameters are 48000Hz, S16_LE, 2 channels, non-blocking mode
Poll mode: no
Loop limit is 480000 frames, minimum latency = 128, maximum latency = 128
Hardware PCM card 0 'HDA Intel PCH' device 0 subdevice 0
Its setup is:
  stream       : PLAYBACK
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 2
  rate         : 48000
  exact rate   : 48000 (48000/1)
  msbits       : 16
  buffer_size  : 128
  period_size  : 64
  period_time  : 1333
  tstamp_mode  : NONE
  tstamp_type  : MONOTONIC
  period_step  : 1
  avail_min    : 64
  period_event : 0
  start_threshold  : 2147483647
  stop_threshold   : 128
  silence_threshold: 0
  silence_size : 0
  boundary     : 4611686018427387904
  appl_ptr     : 0
  hw_ptr       : 0
Hardware PCM card 0 'HDA Intel PCH' device 0 subdevice 0
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  : 128
  period_size  : 64
  period_time  : 1333
  tstamp_mode  : NONE
  tstamp_type  : MONOTONIC
  period_step  : 1
  avail_min    : 64
  period_event : 0
  start_threshold  : 2147483647
  stop_threshold   : 128
  silence_threshold: 0
  silence_size : 0
  boundary     : 4611686018427387904
  appl_ptr     : 0
  hw_ptr       : 0
Trying latency 128 frames, 2666.667us, 2.666667ms (375.0000Hz)
Failure
Playback:
*** frames = 90720 ***
  state       : XRUN
  trigger_time: 967.658489
  tstamp      : 0.000000
  delay       : 0
  avail       : 216
  avail_max   : 216
Capture:
*** frames = 90592 ***
  state       : XRUN
  trigger_time: 967.658489
  tstamp      : 0.000000
  delay       : 0
  avail       : 88
  avail_max   : 88
Maximum read: 16 frames
Maximum read latency: 333.333us, 0.333333ms (3000.0000Hz)
Hardware sync
```

I get an **XRUN** during the test execution.
I can reproduce the same error on multiple boards for multiple audio cards and on different Linux distribution just changing the Linux kernel version.
The problem was originally reported at:
[AES67 Linux daemon: Latency test fails with Linux kernel starting from 5.10.0x](https://github.com/bondagit/aes67-linux-daemon/issues/79)

I am interested in testing a with low latency (-m 128 -M 128).
My guess is that something changed in the Linux audio core and the latency application has to be adapted.
Any idea ?

Issue URL     : https://github.com/alsa-project/alsa-lib/issues/285
Repository URL: https://github.com/alsa-project/alsa-lib