netdev - Re: [RFT net-next] net: stmmac: Rework coalesce timer and fix multi-queue races

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Date:   Mon, 3 Sep 2018 10:36:47 +0100
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>, <netdev@...r.kernel.org>
CC:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        "David S. Miller" <davem@...emloft.net>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>
Subject: Re: [RFT net-next] net: stmmac: Rework coalesce timer and fix
 multi-queue races

Hi Jerome,

On 03-09-2018 09:56, Jerome Brunet wrote:
> On Thu, 2018-08-30 at 11:37 +0100, Jose Abreu wrote:
>> [ As for now this is only for testing! ]
>>
>> This follows David Miller advice and tries to fix coalesce timer in
>> multi-queue scenarios.
>>
>> We are now using per-queue coalesce values and per-queue TX timer. This
>> assumes that tx_queues == rx_queues, which can not be necessarly true.
>> Official patch will need to have this fixed.
>>
>> Coalesce timer default values was changed to 1ms and the coalesce frames
>> to 25.
>>
>> Tested in B2B setup between XGMAC2 and GMAC5.
> Tested on Amlogic meson-axg-s400. No regression seen so far.
> (arch/arm64/boot/dts/amlogic/meson-axg-s400.dts)
>
> As far as I understand from the device tree parsing, this platform (and all
> other amlogic platforms) use single queue.

Thanks for testing! I will send a formal patch once I get around
the problem of rx queues != tx queues.

>
> ---
>
> Jose,
>
> On another topic doing iperf3 test on amlogic's devices we seen a strange
> behavior.
>
> Doing Tx or Rx test usually works fine (700MBps to 900MBps depending on the
> platform). However, when doing both Rx and Tx at the same time, We see the Tx
> throughput dropping significantly (~30MBps) and lot of TCP retries.
>
> Would you any idea what might be our problem ? or how to start investigating
> this ?
>

I'm not able to reproduce this here but I'm using multiple queue.
I will try with single queue. In the meantime please try this
patch (it shall be applied directly on top of this RFT):


--->8
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index ae26a6e8608e..1407975320aa 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2210,8 +2210,7 @@ static int stmmac_init_dma_engine(struct
stmmac_priv *priv)
                stmmac_init_tx_chan(priv, priv->ioaddr,
priv->plat->dma_cfg,
                                    tx_q->dma_tx_phy, chan);
 
-               tx_q->tx_tail_addr = tx_q->dma_tx_phy +
-                           (DMA_TX_SIZE * sizeof(struct dma_desc));
+               tx_q->tx_tail_addr = tx_q->dma_tx_phy;
                stmmac_set_tx_tail_ptr(priv, priv->ioaddr,
                                       tx_q->tx_tail_addr, chan);
        }
@@ -3004,6 +3003,7 @@ static netdev_tx_t stmmac_tso_xmit(struct
sk_buff *skb, struct net_device *dev)
 
        netdev_tx_sent_queue(netdev_get_tx_queue(dev, queue),
skb->len);
 
+       tx_q->tx_tail_addr = tx_q->dma_tx_phy + (tx_q->cur_tx *
sizeof(*desc));
        stmmac_set_tx_tail_ptr(priv, priv->ioaddr,
tx_q->tx_tail_addr, queue);
 
        if (priv->tx_coal_timer && !tx_q->tx_timer_active) {
@@ -3223,6 +3223,8 @@ static netdev_tx_t stmmac_xmit(struct
sk_buff *skb, struct net_device *dev)
        netdev_tx_sent_queue(netdev_get_tx_queue(dev, queue),
skb->len);
 
        stmmac_enable_dma_transmission(priv, priv->ioaddr);
+
+       tx_q->tx_tail_addr = tx_q->dma_tx_phy + (tx_q->cur_tx *
sizeof(*desc));
        stmmac_set_tx_tail_ptr(priv, priv->ioaddr,
tx_q->tx_tail_addr, queue);
 
        if (priv->tx_coal_timer && !tx_q->tx_timer_active) {
--->8

Thanks and Best Regards,
Jose Miguel Abreu