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Date: Mon, 16 Oct 2023 21:37:58 +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 5:37 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
>
> 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.
>
Looking a bit at fec, I think fec_enet_txq_put_hdr_tso() is bogus...
txq->tso_hdrs should be properly aligned by definition.
If FEC_QUIRK_SWAP_FRAME is requested, better copy the right thing, not
original skb->data ???
diff --git a/drivers/net/ethernet/freescale/fec_main.c
b/drivers/net/ethernet/freescale/fec_main.c
index 77c8e9cfb44562e73bfa89d06c5d4b179d755502..520436d579d66cc3263527373d754a206cb5bcd6
100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -753,7 +753,6 @@ fec_enet_txq_put_hdr_tso(struct fec_enet_priv_tx_q *txq,
struct fec_enet_private *fep = netdev_priv(ndev);
int hdr_len = skb_tcp_all_headers(skb);
struct bufdesc_ex *ebdp = container_of(bdp, struct bufdesc_ex, desc);
- void *bufaddr;
unsigned long dmabuf;
unsigned short status;
unsigned int estatus = 0;
@@ -762,11 +761,11 @@ fec_enet_txq_put_hdr_tso(struct fec_enet_priv_tx_q *txq,
status &= ~BD_ENET_TX_STATS;
status |= (BD_ENET_TX_TC | BD_ENET_TX_READY);
- bufaddr = txq->tso_hdrs + index * TSO_HEADER_SIZE;
dmabuf = txq->tso_hdrs_dma + index * TSO_HEADER_SIZE;
- if (((unsigned long)bufaddr) & fep->tx_align ||
- fep->quirks & FEC_QUIRK_SWAP_FRAME) {
- memcpy(txq->tx_bounce[index], skb->data, hdr_len);
+ if (fep->quirks & FEC_QUIRK_SWAP_FRAME) {
+ void *bufaddr = txq->tso_hdrs + index * TSO_HEADER_SIZE;
+
+ memcpy(txq->tx_bounce[index], bufaddr, hdr_len);
bufaddr = txq->tx_bounce[index];
if (fep->quirks & FEC_QUIRK_SWAP_FRAME)
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