On Mon, Oct 05, 2015 at 07:27:23PM +0530, Jayan John wrote: > We are developing a custom USB device on a iMX6q platform with a Chipidea > HDRC. The device uses a single NCM interface for communication with another > OTG device i.e. Chipidea HDRC again. I see very poor iperf UDP performance > after role reversal with iperf server running on gadget. > > Kernel: 3.10.17 using Wandboard config > > Test sequence: > 1. Connect both boards (board A and board B) using OTG cable > 2. Board A is assigned as A device and board B is assigned as B device > 3. B device initiates role reversal > echo -n host > /sys/kernel/debug/ci_hdrc.0/role > 4. A device switches to gadget mode > echo -n gadget > /sys/kernel/debug/ci_hdrc.0/role > 5. Assign IPV6 address on board A (now gadget).. ifconfig usb0 2012::1/64 up > 6. Assign IPV6 address on board B (now host).. ifconfig usb0 2012::2/64 up > 7. Run iperf server on board A.. iperf -V -s -u > 8. Run iperf client on board B.. iperf -u -t 10 -V -c 2012::1 -b 150M > > iperf server logs: > [ 4] local fe80::6cc9:b6ff:fec5:be28 port 5001 connected with > fe80::54e0:86ff:fea6:8987 port 35629 > [ 4] 0.0-10.0 sec 63.7 MBytes 53.4 Mbits/sec 0.171 ms 61701/107109 (58%) > [ 4] 0.0-10.0 sec 1 datagrams received out-of-order > [ 3] local fe80::6cc9:b6ff:fec5:be28 port 5001 connected with > fe80::54e0:86ff:fea6:8987 port 33609 > [ 3] 0.0-10.0 sec 62.1 MBytes 52.1 Mbits/sec 0.215 ms 62551/106825 (59%) > [ 3] 0.0-10.0 sec 1 datagrams received out-of-order > > Query: > 1. The UDP packet loss is seen only in the case of iperf server on gadget > after role reversal. I see there are patches (12) from Peter for performance > improvements on the newer kernels. Will they help? If you only see this problem after role switch, compare the controller registers may help it. > 2. The issue is not seen if UDP socket buffer size/ datagram size on iperf is > increased i.e. iperf -u -t 10 -l 32k -V -c 2012::1 -b 150M. Is this only > hiding an issue with Chipidea driver e.g. TXFIFO or burst size? > 3. Should ncm be tweaked to have different buffer size or NTB handling? NCM stack may be updated from v3.10, I just tried (without role switch), it can get 110Mbps, and about 3% loss rate using your command at v4.3-rc1. -- Best Regards, Peter Chen -- 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
