On Thu, Oct 8, 2015 at 1:37 PM, Peter Chen <peter.c...@freescale.com> wrote:
> 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

Thanks Peter, I will try that. I saw the packet loss only after role
switch.

I will close this thread for now, as I intend to make a kernel upgrade
before I continue investigation on this issue.

I will update the community/ push a patch when I root cause/ fix this.

BR,
Jayan
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