[LAU] anyone checked out new USB reduced latency patch?

Robin Gareus robin at gareus.org
Mon Jun 7 17:11:57 CEST 2021

On 6/6/21 8:16 PM, Clemens Ladisch wrote:
> Chris Caudle wrote:
>> I just saw that this is probably going in the 5.14 kernel:
>> https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/commit/?h=for-next&id=9ce650a75a3b262c90789b42aedee8fc2ee04d53
>> "USB-audio driver behaves a bit strangely for the playback stream --
>> namely, it starts sending silent packets at PCM prepare state while
>> the actual data is submitted at first when the trigger START is kicked
>> off. [...]
>> This patch tries to revert the workaround and lets the URB submission
>> starting at PCM trigger for the playback again.
> Please note that this reduces only the time between the stream being
> started and the first sample actually being played.  It does _not_
> reduce the latency in the steady state, because the USB queue length
> does not change.

Does this help to reduce the random systemic latency of USB/ALSA devices?

Currently with USB device there is up to the buffer size (but at most
20ms) additional I/O latency. The delay is different every time the
device is started, or after an xrun occurs. It would be great if this
doesn't need to be measured every time.


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