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Date: Mon, 16 Oct 2023 17:36:52 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Eric Dumazet <edumazet@...gle.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
Hello again,
> > > # 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?
Apparently I've been too enthusiastic. After sending this e-mail I've
re-generated an image with iproute2 and dd'ed the whole image into an
SD card, while until now I was just updating the kernel/DT manually and
got the same performances as above without the gro size trick. I need
to clarify this further.
Thanks,
Miquèl
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