RX packet loss on i.MX6Q running 4.2-rc7

[Jon Nettleton]

On Fri, Aug 21, 2015 at 12:30 AM, Clemens Gruber
<clemens.gruber at pqgruber.com> wrote:
> Hi,
>
> I am experiencing massive RX packet loss on my i.MX6Q (Chip rev 1.3) on Linux
> 4.2-rc7 with a Marvell 88E1510 Gigabit Ethernet PHY connected over RGMII.
> I noticed it when doing an UDP benchmark with iperf3. When sending UDP packets
> from a Debian PC to the i.MX6 with a rate of 100 Mbit/s, 99% of the packets are
> lost. With a rate of 10 Mbit/s, we are still losing 93% of all packets. TCP RX
> does suffer from packet loss too, but still achieves about 211 Mbit/s.
> TX is not affected.
>
> Steps to reproduce:
> On the i.MX6: iperf3 -s
> On a desktop PC:  iperf3 -b 10M -u -c MX6IP
>
> The iperf3 results:
> [ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total
> [  4]   0.00-10.00  sec  11.8 MBytes  9.90 Mbits/sec  0.687 ms  1397/1497 (93%)
>
> During the 10 Mbit UDP test, the IEEE_rx_macerr counter increased to 5371.
> ifconfig eth0 shows:
>  RX packets:9216 errors:5248 dropped:170 overruns:5248 frame:5248
>  TX packets:83 errors:0 dropped:0 overruns:0 carrier:0
>  collisions:0
>
> Here are the TCP results with iperf3 -c MX6IP:
> [ ID] Interval           Transfer     Bandwidth       Retr
> [  4]   0.00-10.00  sec   252 MBytes   211 Mbits/sec  4343             sender
> [  4]   0.00-10.00  sec   251 MBytes   211 Mbits/sec                  receiver
>
> During the TCP test, IEEE_rx_macerr increased to 4059.
> ifconfig eth0 shows:
> RX packets:186368 errors:4206 dropped:50 overruns:4206 frame:4206
> TX packets:41861 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0
>
> Freescale errata entry ERR004512 did mention a RX FIFO overrun. Is this related?
>
> Forcing pause frames via ethtool -A eth0 rx on tx on, does not improve it:
> Same amount of UDP packet loss with reduced TCP throughput of 190 Mbit/s.
> IEEE_rx_macerr increased up to 5232 during UDP 10Mbit and up to 4270 for TCP.
>
> I am already using the MX6QDL_PAD_GPIO_6__ENET_IRQ workaround, which solved the
> ping latency issues from ERR006687 but not the packet loss problem.
>
> I read through the mailing list archives and found a discussion between Russell
> King, Marek Vasut, Eric Nelson, Fugang Duan and others about a similar problem.
> I therefore added you and contributors to fec_main.c to the CC.
>
> One suggestion I found, was adding udelay(210); to fec_enet_rx():
> https://lkml.org/lkml/2014/8/22/88
> But this also did not reduce the packet loss. (I added it to the fec_enet_rx
> function just before return pkt_received; but I still got 93% packet loss)
>
> Does anyone have the equipment/setup to trace an i.MX6Q during UDP RX traffic
> from iperf3 to find the root cause of this packet loss problem?
>
> What else could we do to fix this?
>

This is a bug in iperf3's UDP tests.  Do the same test with iperf2 and
you will see expected performance.  I believe there is a bug open in
github about it.

-Jon