[alsa-devel] Buffer size for ALSA USB PCM audio

Clemens Ladisch clemens at ladisch.de
Tue Aug 27 22:03:26 CEST 2013

Alan Stern wrote:
> On Tue, 27 Aug 2013, Clemens Ladisch wrote:
>> The current algorithm uses very short capture URBs to ensure that _some_
>> URB is completed as soon as possible after a period ends.
>> [...]
>> I'd suggest to keep the old calculation for capture URBs.  It would
>> make sense to use longer capture URBs only if the period size is
>> relatively large.
> Okay.  What about playback endpoints with implicit sync?  The current
> driver treats them the same as capture endpoints.  Is that really the
> right thing to do?

The only reason to not have an interrupt after each packet is to avoid
the interrupt overhead (for both CPU and power); shorter URBs would
result in a more precise DMA position reported to user space.  If there
is already an interrupt for some capture URB (or for the feedback packet
in case of explicit feedback), we might as well handle the playback
packets so far.


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