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. -- robin
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