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? 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? -- 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
