no_period_wakeup, axfer and --sched-model=timer

[Amadeusz Sławiński]

On 5/13/2021 3:25 PM, Takashi Sakamoto wrote:
> Hi,
> 
> On Thu, May 13, 2021 at 01:34:25PM +0200, Amadeusz Sławiński wrote:
>> I was checking some stuff relater to NO_PERIOD_WAKEUP and noticed that axfer
>> has support for using either --sched-model=irq or --sched-model=timer.
>> However from few quick tests it seems like it doesn't work?
>>
>> $ aplay -l
>> **** List of PLAYBACK Hardware Devices ****
>> card 0: PCH [HDA Intel PCH], device 0: ALC283 Analog [ALC283 Analog]
>>    Subdevices: 1/1
>>    Subdevice #0: subdevice #0
>>
>>
>> When using  --sched-model=irq  it transfers data until I press Ctrl+C
>>
>> $ axfer transfer playback --sched-model=irq -D hw:0,0 -r 48000 -c2 -f S16_LE
>> /dev/urandom
>> PLAYBACK: Format 'Signed 16 bit Little Endian', Rate 48000 Hz, Channels
>> 'Stereo'
>> ^CPLAYBACK: Expected 4611686018427387903frames, Actual 163960frames
>> Aborted by signal: Interrupt
>>
>>
>> However with  --sched-model=timer  it time outs by itself:
>>
>> $ axfer transfer playback --sched-model=timer -D hw:0,0 -r 48000 -c2 -f
>> S16_LE /dev/urandom
>> PLAYBACK: Format 'Signed 16 bit Little Endian', Rate 48000 Hz, Channels
>> 'Stereo'
>> Fail to process frames: Connection timed out
>> PLAYBACK: Expected 4611686018427387903frames, Actual 16304frames
>>
>>
>> How well is NO_PERIOD_WAKEUP tested/supported? Is it a bug in axfer or
>> perhaps some issue in kernel code?
>>
>>  From some debugging I did, I have my suspicions that it gets stuck on poll
>> in:
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/core/pcm_native.c?id=c06a2ba62fc401b7aaefd23f5d0bc06d2457ccc1#n3489
>> waiting for runtime->sleep to wake it, but seems like it never happens.
>>
>> What do you think?
> 
> It's a regression added by a commit e5e6a7838b06 ("axfer: return ETIMEDOUT
> when no event occurs after waiter expiration"), and the -ETIMEDOUT come
> neither from ALSA PCM core nor alsa-lib. Thanks for your reporting!
> 
>   * https://github.com/alsa-project/alsa-utils/commit/e5e6a7838b06
> 
> As a quick fix, please revert the commit. I'll post better fixes later.
> 
> After the revert, it looks work well under my hardware:
> 

Yes, I can confirm, that it fixes the problem. Thanks for quick workaround!