I just read the notes from the last two weeks of USB latency debugging. Very interesting results! Could somebody who was there please document whether any of the tests were performed with a hub in the system, and what the topology was in that case?
Sarah says: - Re-try the experiment of putting more load on the bus, but rather than using a kernel driver to create the load, use some existing libusb-based application. Perhaps a gphoto2-based camera? Hypothesis under test: There's something wrong with usbfs, and creating load with a kernel driver is bypassing it somehow. If creating load using only usbfs doesn't improve the latency measurements, then this hypothesis looks likely. - Ask Alan Stern for advice, CC'ing the linux-usb and libusb mailing lists. If there's a problem in the UHCI driver, or a documented limitation in the specification, writing a kernel driver isn't going to help. If there's an issue with usbfs, that should get fixed. - Try turning on CONFIG_USB_EHCI_TT_NEWSCHED and seeing if that helps when the device is behind a high-speed hub. (It won't have any effect when the GFE is plugged into a host port directly, since in that case the UHCI driver will claim the device, rather than the EHCI driver.) - Try turning off CONFIG_USB_DEBUG and seeing if that makes the delay go away. Jamey _______________________________________________ psas-avionics mailing list psas-avionics@lists.psas.pdx.edu http://lists.psas.pdx.edu/mailman/listinfo/psas-avionics
