On Tue, 27 Aug 2013, James Stone wrote:

This does not help at all with running jackd at lower latencies.

With this patch, I get xruns at 128 frames/period or less with jackd (accompanied by iso underrun messages), whereas with vanilla 3.10.9 (which now has both yours and Clemen's patches applied), performance is extremely good (64 frames per period possible).

Was this was both recording and playback, or playback only? If you were doing both, what happens with just playback?

Assuming you see the same problem with just playback, please collect a usbmon trace showing one or two of those underruns at say 64 frames/period. And for comparison, it would be nice to have a usbmon trace showing a couple of seconds of normal operation under vanilla 3.10.9.

Alan Stern