On Wed, Nov 20, 2013 at 05:16:12PM -0000, David Laight wrote: > > Ok, so the networking layer should be fine. However, with the current > > patch, if the mass storage driver sends down a scatter-gather list > > that's bigger than a ring segment, or needs to be split up so it doesn't > > cross 64K boundaries, then the URB submission will fail. We don't want > > that to happen. > > My suspicion is that long SG lists are unusual - otherwise the > ring expansion code would have been needed much earlier. > > Can anyone remember whether that was needed because of long SG lists > or because of large numbers of outstanding requests? > > I've seen it for network cards - but only because usbnet sends > down far too many tx buffers. It was added because USB video and audio drivers queue isochronous URBs with lots of buffers for each service interval. So basically, lots of outstanding requests, not long SG lists was the driving motivation to add the ring expansion. Sarah Sharp -- 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
