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Date: Wed, 21 Oct 2020 11:00:08 +1100
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: Joel Stanley <joel@....id.au>, Jakub Kicinski <kuba@...nel.org>,
"David S . Miller" <davem@...emloft.net>,
Dylan Hung <dylan_hung@...eedtech.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-aspeed@...ts.ozlabs.org
Subject: Re: [PATCH] net: ftgmac100: Ensure tx descriptor updates are visible
On Wed, 2020-10-21 at 08:36 +1030, Joel Stanley wrote:
> We must ensure the tx descriptor updates are visible before updating
> the tx pointer.
>
> This resolves the tx hangs observed on the 2600 when running iperf:
To clarify the comment here. This doesn't ensure they are visible to
the hardware but to other CPUs. This is the ordering vs start_xmit and
tx_complete.
Cheers,
Ben.
> root@...2600:~# iperf3 -c 192.168.86.146 -R
> Connecting to host 192.168.86.146, port 5201
> Reverse mode, remote host 192.168.86.146 is sending
> [ 5] local 192.168.86.173 port 43886 connected to 192.168.86.146
> port 5201
> [ ID] Interval Transfer Bitrate
> [ 5] 0.00-1.00 sec 90.7 MBytes 760 Mbits/sec
> [ 5] 1.00-2.00 sec 91.7 MBytes 769 Mbits/sec
> [ 5] 2.00-3.00 sec 91.7 MBytes 770 Mbits/sec
> [ 5] 3.00-4.00 sec 91.7 MBytes 769 Mbits/sec
> [ 5] 4.00-5.00 sec 91.8 MBytes 771 Mbits/sec
> [ 5] 5.00-6.00 sec 91.8 MBytes 771 Mbits/sec
> [ 5] 6.00-7.00 sec 91.9 MBytes 771 Mbits/sec
> [ 5] 7.00-8.00 sec 91.4 MBytes 767 Mbits/sec
> [ 5] 8.00-9.00 sec 91.3 MBytes 766 Mbits/sec
> [ 5] 9.00-10.00 sec 91.9 MBytes 771 Mbits/sec
> [ 5] 10.00-11.00 sec 91.8 MBytes 770 Mbits/sec
> [ 5] 11.00-12.00 sec 91.8 MBytes 770 Mbits/sec
> [ 5] 12.00-13.00 sec 90.6 MBytes 761 Mbits/sec
> [ 5] 13.00-14.00 sec 45.2 KBytes 370 Kbits/sec
> [ 5] 14.00-15.00 sec 0.00 Bytes 0.00 bits/sec
> [ 5] 15.00-16.00 sec 0.00 Bytes 0.00 bits/sec
> [ 5] 16.00-17.00 sec 0.00 Bytes 0.00 bits/sec
> [ 5] 17.00-18.00 sec 0.00 Bytes 0.00 bits/sec
> [ 67.031671] ------------[ cut here ]------------
> [ 67.036870] WARNING: CPU: 1 PID: 0 at net/sched/sch_generic.c:442
> dev_watchdog+0x2dc/0x300
> [ 67.046123] NETDEV WATCHDOG: eth2 (ftgmac100): transmit queue 0
> timed out
>
> Fixes: 52c0cae87465 ("ftgmac100: Remove tx descriptor accessors")
> Signed-off-by: Joel Stanley <joel@....id.au>
> ---
> drivers/net/ethernet/faraday/ftgmac100.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/net/ethernet/faraday/ftgmac100.c
> b/drivers/net/ethernet/faraday/ftgmac100.c
> index 331d4bdd4a67..15cdfeb135b0 100644
> --- a/drivers/net/ethernet/faraday/ftgmac100.c
> +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> @@ -653,6 +653,11 @@ static bool ftgmac100_tx_complete_packet(struct
> ftgmac100 *priv)
> ftgmac100_free_tx_packet(priv, pointer, skb, txdes, ctl_stat);
> txdes->txdes0 = cpu_to_le32(ctl_stat & priv-
> >txdes0_edotr_mask);
>
> + /* Ensure the descriptor config is visible before setting the
> tx
> + * pointer.
> + */
> + smp_wmb();
> +
> priv->tx_clean_pointer = ftgmac100_next_tx_pointer(priv,
> pointer);
>
> return true;
> @@ -806,6 +811,11 @@ static netdev_tx_t
> ftgmac100_hard_start_xmit(struct sk_buff *skb,
> dma_wmb();
> first->txdes0 = cpu_to_le32(f_ctl_stat);
>
> + /* Ensure the descriptor config is visible before setting the
> tx
> + * pointer.
> + */
> + smp_wmb();
> +
> /* Update next TX pointer */
> priv->tx_pointer = pointer;
>
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