On Fri, 4 Dec 2009, Pete Zaitcev wrote: > On Fri, 4 Dec 2009 11:59:25 -0800, Greg KH <greg@xxxxxxxxx> wrote: > > On Fri, Dec 04, 2009 at 12:46:57PM -0700, Pete Zaitcev wrote: > > > > A user found that copying to a USB disk crowds out ISO transfers > > > to audio. How is this even possible? > > > > > > https://bugzilla.redhat.com/show_bug.cgi?id=517438 > > > > > > > Whilst starting a Torrent with Transmission on a VFAT USB hard drive, audio > > > > (through a USB 5.1 sound card) started skipping like nobody's business. > > > > > > > ALSA sound/usb/usbaudio.c:882: cannot submit datapipe for urb 0, error -28: not enough bandwidth > > > > ALSA sound/usb/usbaudio.c:882: cannot submit datapipe for urb 0, error -28: not enough bandwidth I would guess that the problem is the extra computational load caused by running Torrent. It could prevent the usbaudio driver from running in a timely fashion (because of the added interrupt latency), thereby losing its bandwidth allocation. A usbmon trace would tell whether this is really what's happening. > > > On 2.6.31-rc5-git2. > > > > That should be normal, bulk is taking up the bandwidth for the bus, so > > iso can't be scheduled. > > > > Or am I missing something? > > The whole reason for ISO to exist is to receive the guaranteed bandwidth, > isn't it (see clause 3.3 of 2.0 spec)? > > I understand that until the ISO URB is submitted, there's no way for the > HCD to know that it should allocate the bandwidth. What is our solution, > then? Should we create some sort of "channels" that allocate the bandwidth > (what spec calls "prenegotiated")? That is more or less our plan (preallocate periodic bandwidth as soon as a config or an altsetting is installed). It's going to take a while to implement, however. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
