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Message-ID: <CANn89iKz61-TNya=cQpaUECoQuEGd6pLBUcuJAoKHA2rKZoDEA@mail.gmail.com>
Date: Mon, 16 Oct 2023 17:06:29 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>, Wei Fang <wei.fang@....com>,
Shenwei Wang <shenwei.wang@....com>, Clark Wang <xiaoning.wang@....com>, davem@...emloft.net,
kuba@...nel.org, pabeni@...hat.com, linux-imx@....com, netdev@...r.kernel.org,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Alexandre Belloni <alexandre.belloni@...tlin.com>,
Maxime Chevallier <maxime.chevallier@...tlin.com>, Andrew Lunn <andrew@...n.ch>,
Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: Ethernet issue on imx6
On Mon, Oct 16, 2023 at 3:59 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
>
> Hi Eric,
>
> edumazet@...gle.com wrote on Mon, 16 Oct 2023 13:49:25 +0200:
>
> > On Fri, Oct 13, 2023 at 10:40 AM Miquel Raynal
> > <miquel.raynal@...tlin.com> wrote:
> > >
> > > Hi Russell,
> > >
> > > linux@...linux.org.uk wrote on Thu, 12 Oct 2023 20:39:11 +0100:
> > >
> > > > On Thu, Oct 12, 2023 at 07:34:10PM +0200, Miquel Raynal wrote:
> > > > > Hello,
> > > > >
> > > > > I've been scratching my foreheads for weeks on a strange imx6
> > > > > network issue, I need help to go further, as I feel a bit clueless now.
> > > > >
> > > > > Here is my setup :
> > > > > - Custom imx6q board
> > > > > - Bootloader: U-Boot 2017.11 (also tried with a 2016.03)
> > > > > - Kernel : 4.14(.69,.146,.322), v5.10 and v6.5 with the same behavior
> > > > > - The MAC (fec driver) is connected to a Micrel 9031 PHY
> > > > > - The PHY is connected to the link partner through an industrial cable
> > > >
> > > > "industrial cable" ?
> > >
> > > It is a "unique" hardware cable, the four Ethernet pairs are foiled
> > > twisted pair each and the whole cable is shielded. Additionally there
> > > is the 24V power supply coming from this cable. The connector is from
> > > ODU S22LOC-P16MCD0-920S. The structure of the cable should be similar
> > > to a CAT7 cable with the additional power supply line.
> > >
> > > > > - Testing 100BASE-T (link is stable)
> > > >
> > > > Would that be full or half duplex?
> > >
> > > Ah, yeah, sorry for forgetting this detail, it's full duplex.
> > >
> > > > > The RGMII-ID timings are probably not totally optimal but offer
> > > > > rather good performance. In UDP with iperf3:
> > > > > * Downlink (host to the board) runs at full speed with 0% drop
> > > > > * Uplink (board to host) runs at full speed with <1% drop
> > > > >
> > > > > However, if I ever try to limit the bandwidth in uplink (only), the
> > > > > drop rate rises significantly, up to 30%:
> > > > >
> > > > > //192.168.1.1 is my host, so the below lines are from the board:
> > > > > # iperf3 -c 192.168.1.1 -u -b100M
> > > > > [ 5] 0.00-10.05 sec 113 MBytes 94.6 Mbits/sec 0.044 ms
> > > > > 467/82603 (0.57%) receiver # iperf3 -c 192.168.1.1 -u -b90M
> > > > > [ 5] 0.00-10.04 sec 90.5 MBytes 75.6 Mbits/sec 0.146 ms
> > > > > 12163/77688 (16%) receiver # iperf3 -c 192.168.1.1 -u -b80M
> > > > > [ 5] 0.00-10.05 sec 66.4 MBytes 55.5 Mbits/sec 0.162 ms
> > > > > 20937/69055 (30%) receiver
> > > >
> > > > My setup:
> > > >
> > > > i.MX6DL silicon rev 1.3
> > > > Atheros AR8035 PHY
> > > > 6.3.0+ (no significant changes to fec_main.c)
> > > > Link, being BASE-T, is standard RJ45.
> > > >
> > > > Connectivity is via a bridge device (sorry, can't change that as it
> > > > would be too disruptive, as this is my Internet router!)
> > > >
> > > > Running at 1000BASE-T (FD):
> > > > [ ID] Interval Transfer Bitrate Jitter
> > > > Lost/Total Datagrams [ 5] 0.00-10.01 sec 114 MBytes 95.4
> > > > Mbits/sec 0.030 ms 0/82363 (0%) receiver [ 5] 0.00-10.00 sec
> > > > 107 MBytes 90.0 Mbits/sec 0.103 ms 0/77691 (0%) receiver [ 5]
> > > > 0.00-10.00 sec 95.4 MBytes 80.0 Mbits/sec 0.101 ms 0/69060 (0%)
> > > > receiver
> > > >
> > > > Running at 100BASE-Tx (FD):
> > > > [ ID] Interval Transfer Bitrate Jitter
> > > > Lost/Total Datagrams [ 5] 0.00-10.01 sec 114 MBytes 95.4
> > > > Mbits/sec 0.008 ms 0/82436 (0%) receiver [ 5] 0.00-10.00 sec
> > > > 107 MBytes 90.0 Mbits/sec 0.088 ms 0/77692 (0%) receiver [ 5]
> > > > 0.00-10.00 sec 95.4 MBytes 80.0 Mbits/sec 0.108 ms 0/69058 (0%)
> > > > receiver
> > > >
> > > > Running at 100bASE-Tx (HD):
> > > > [ ID] Interval Transfer Bitrate Jitter
> > > > Lost/Total Datagrams [ 5] 0.00-10.01 sec 114 MBytes 95.3
> > > > Mbits/sec 0.056 ms 0/82304 (0%) receiver [ 5] 0.00-10.00 sec
> > > > 107 MBytes 90.0 Mbits/sec 0.101 ms 1/77691 (0.0013%) receiver [
> > > > 5] 0.00-10.00 sec 95.4 MBytes 80.0 Mbits/sec 0.105 ms 0/69058
> > > > (0%) receiver
> > > >
> > > > So I'm afraid I don't see your issue.
> > >
> > > I believe the issue cannot be at an higher level than the MAC. I also
> > > do not think the MAC driver and PHY driver are specifically buggy. I
> > > ruled out the hardware issue given the fact that under certain
> > > conditions (high load) the network works rather well... But I certainly
> > > see this issue, and when switching to TCP the results are dramatic:
> > >
> > > # iperf3 -c 192.168.1.1
> > > Connecting to host 192.168.1.1, port 5201
> > > [ 5] local 192.168.1.2 port 37948 connected to 192.168.1.1 port 5201
> > > [ ID] Interval Transfer Bitrate Retr Cwnd
> > > [ 5] 0.00-1.00 sec 11.3 MBytes 94.5 Mbits/sec 43 32.5 KBytes
> > > [ 5] 1.00-2.00 sec 3.29 MBytes 27.6 Mbits/sec 26 1.41 KBytes
> > > [ 5] 2.00-3.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
> > > [ 5] 3.00-4.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
> > > [ 5] 4.00-5.00 sec 0.00 Bytes 0.00 bits/sec 5 1.41 KBytes
> > > [ 5] 5.00-6.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
> > > [ 5] 6.00-7.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
> > > [ 5] 7.00-8.00 sec 0.00 Bytes 0.00 bits/sec 1 1.41 KBytes
> > > [ 5] 8.00-9.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
> > > [ 5] 9.00-10.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
> > >
> > > Thanks,
> > > Miquèl
> >
> > Can you experiment with :
> >
> > - Disabling TSO on your NIC (ethtool -K eth0 tso off)
> > - Reducing max GSO size (ip link set dev eth0 gso_max_size 16384)
> >
> > I suspect some kind of issues with fec TX completion, vs TSO emulation.
>
> Wow, appears to have a significant effect. I am using Busybox's iproute
> implementation which does not know gso_max_size, but I hacked directly
> into netdevice.h just to see if it would have an effect. I'm adding
> iproute2 to the image for further testing.
>
> Here is the diff:
>
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2364,7 +2364,7 @@ struct net_device {
> /* TCP minimal MSS is 8 (TCP_MIN_GSO_SIZE),
> * and shinfo->gso_segs is a 16bit field.
> */
> -#define GSO_MAX_SIZE (8 * GSO_MAX_SEGS)
> +#define GSO_MAX_SIZE 16384u
>
> unsigned int gso_max_size;
> #define TSO_LEGACY_MAX_SIZE 65536
>
> And here are the results:
>
> # ethtool -K eth0 tso off
> # iperf3 -c 192.168.1.1 -u -b1M
> Connecting to host 192.168.1.1, port 5201
> [ 5] local 192.168.1.2 port 50490 connected to 192.168.1.1 port 5201
> [ ID] Interval Transfer Bitrate Total Datagrams
> [ 5] 0.00-1.00 sec 123 KBytes 1.01 Mbits/sec 87
> [ 5] 1.00-2.00 sec 122 KBytes 996 Kbits/sec 86
> [ 5] 2.00-3.00 sec 122 KBytes 996 Kbits/sec 86
> [ 5] 3.00-4.00 sec 123 KBytes 1.01 Mbits/sec 87
> [ 5] 4.00-5.00 sec 122 KBytes 996 Kbits/sec 86
> [ 5] 5.00-6.00 sec 122 KBytes 996 Kbits/sec 86
> [ 5] 6.00-7.00 sec 123 KBytes 1.01 Mbits/sec 87
> [ 5] 7.00-8.00 sec 122 KBytes 996 Kbits/sec 86
> [ 5] 8.00-9.00 sec 122 KBytes 996 Kbits/sec 86
> [ 5] 9.00-10.00 sec 123 KBytes 1.01 Mbits/sec 87
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
> [ 5] 0.00-10.00 sec 1.19 MBytes 1.00 Mbits/sec 0.000 ms 0/864 (0%) sender
> [ 5] 0.00-10.05 sec 1.11 MBytes 925 Kbits/sec 0.045 ms 62/864 (7.2%) receiver
> iperf Done.
> # iperf3 -c 192.168.1.1
> Connecting to host 192.168.1.1, port 5201
> [ 5] local 192.168.1.2 port 34792 connected to 192.168.1.1 port 5201
> [ ID] Interval Transfer Bitrate Retr Cwnd
> [ 5] 0.00-1.00 sec 1.63 MBytes 13.7 Mbits/sec 30 1.41 KBytes
> [ 5] 1.00-2.00 sec 7.40 MBytes 62.1 Mbits/sec 65 14.1 KBytes
> [ 5] 2.00-3.00 sec 7.83 MBytes 65.7 Mbits/sec 109 2.83 KBytes
> [ 5] 3.00-4.00 sec 2.49 MBytes 20.9 Mbits/sec 46 19.8 KBytes
> [ 5] 4.00-5.00 sec 7.89 MBytes 66.2 Mbits/sec 109 2.83 KBytes
> [ 5] 5.00-6.00 sec 255 KBytes 2.09 Mbits/sec 22 2.83 KBytes
> [ 5] 6.00-7.00 sec 4.35 MBytes 36.5 Mbits/sec 74 41.0 KBytes
> [ 5] 7.00-8.00 sec 10.9 MBytes 91.8 Mbits/sec 34 45.2 KBytes
> [ 5] 8.00-9.00 sec 5.35 MBytes 44.9 Mbits/sec 82 1.41 KBytes
> [ 5] 9.00-10.00 sec 1.37 MBytes 11.5 Mbits/sec 73 1.41 KBytes
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval Transfer Bitrate Retr
> [ 5] 0.00-10.00 sec 49.5 MBytes 41.5 Mbits/sec 644 sender
> [ 5] 0.00-10.05 sec 49.3 MBytes 41.1 Mbits/sec receiver
> iperf Done.
>
> There is still a noticeable amount of drop/retries, but overall the
> results are significantly better. What is the rationale behind the
> choice of 16384 in particular? Could this be further improved?
Use of fec driver was the common trigger with another thread discussed
in netdev@
Can you go back to standard gso_max_size, and apply the patch found here :
https://lore.kernel.org/netdev/CANn89iJUBujG2AOBYsr0V7qyC5WTgzx0GucO=2ES69tTDJRziw@mail.gmail.com/
You could possibly compile a more recent iproute2/ip command, and play
with gso_max_size,
I wonder if soft tso used in fec driver could have some corner cases.
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