7 Jun
2021
7 Jun
'21
7:12 p.m.
On 6/6/21 8:16 PM, Clemens Ladisch wrote:
Chris Caudle wrote:
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.
--
robin
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=f…
"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.