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

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Date:   Mon, 03 Sep 2018 12:16:25 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     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

On Mon, 2018-09-03 at 10:36 +0100, Jose Abreu wrote:
> 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):

No notable change. Rx is fine but Tx:
[  5]   3.00-4.00   sec  3.55 MBytes  29.8 Mbits/sec   51   12.7 KBytes

I suppose the problem as something to do with the retries. When doing Tx test
alone, we don't have such a things a throughput where we expect it to be.

By the way, your mailer (and its auto 80 column rule I suppose) made the patch
below a bit harder to apply

> 
> 
> --->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