netdev - Re: [PATCH net-next v3 09/10] net: ethernet: mtk-star-emac: separate tx/rx handling with two NAPIs

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Date:   Tue, 28 Jun 2022 13:44:31 +0800
From:   Biao Huang <biao.huang@...iatek.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     David Miller <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Fabien Parent <fparent@...libre.com>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        Yinghua Pan <ot_yinghua.pan@...iatek.com>,
        <srv_heupstream@...iatek.com>,
        Macpaul Lin <macpaul.lin@...iatek.com>
Subject: Re: [PATCH net-next v3 09/10] net: ethernet: mtk-star-emac:
 separate tx/rx handling with two NAPIs

Dear Jakub,
	Thanks for your comments~

On Thu, 2022-06-23 at 21:34 -0700, Jakub Kicinski wrote:
> On Wed, 22 Jun 2022 17:05:44 +0800 Biao Huang wrote:
> > +	if (rx || tx) {
> > +		spin_lock_irqsave(&priv->lock, flags);
> > +		/* mask Rx and TX Complete interrupt */
> > +		mtk_star_disable_dma_irq(priv, rx, tx);
> > +		spin_unlock_irqrestore(&priv->lock, flags);
> 
> You do _irqsave / _irqrestore here
We should invoke spin_lock, no need save/store irq here.
> 
> > +		if (rx)
> > +			__napi_schedule_irqoff(&priv->rx_napi);
> > +		if (tx)
> > +			__napi_schedule_irqoff(&priv->tx_napi);
> 
> Yet assume _irqoff here.
> 
> So can this be run from non-IRQ context or not?
seems __napi_schedule is more proper for our case, we'll modify it in
next send.
> 
> > -	if (mtk_star_ring_full(ring))
> > +	if (unlikely(mtk_star_tx_ring_avail(ring) < MAX_SKB_FRAGS + 1))
> >  		netif_stop_queue(ndev);
> 
> Please look around other drivers (like ixgbe) and copy the way they
> handle safe stopping of the queues. You need to add some barriers and
> re-check after disabling.
Yes, we look drivers from other vendors, and will do similar thing in
next send.
> 
> > -	spin_unlock_bh(&priv->lock);
> > -
> >  	mtk_star_dma_resume_tx(priv);
> >  
> >  	return NETDEV_TX_OK;
> 
> 
> > +	while ((entry != head) && (count < MTK_STAR_RING_NUM_DESCS -
> > 1)) {
> >  
> 
> Parenthesis unnecessary, so is the empty line after the while ().
Yes, the empty line will be removed in next send.
> 
> >  		ret = mtk_star_tx_complete_one(priv);
> >  		if (ret < 0)
> >  			break;
> > +
> > +		count++;
> > +		pkts_compl++;
> > +		bytes_compl += ret;
> > +		entry = ring->tail;
> >  	}
> >  
> > +	__netif_tx_lock_bh(netdev_get_tx_queue(priv->ndev, 0));
> >  	netdev_completed_queue(ndev, pkts_compl, bytes_compl);
> > +	__netif_tx_unlock_bh(netdev_get_tx_queue(priv->ndev, 0));
> 
> what are you taking this lock for?
In this version, we encounter some issue related to
__QUEUE_STATE_STACK_OFF, 
and if we add __netif_tx_lock_bh here, it disappears.

When recieve your comments, we survey netdev_completed_queue handles in
drivers from other vendors, we beleive the __QUEUE_STATE_STACK_OFF
issue may caused by unproper usage of __napi_schedule_irqoff in
previous lines, and we'll remove __netif_tx_lock_bh, and have another
try.

If our local stress test pass, corresponding modification will be added
in next send.
> 
> > -	if (wake && netif_queue_stopped(ndev))
> > +	if (unlikely(netif_queue_stopped(ndev)) &&
> > +	    (mtk_star_tx_ring_avail(ring) > MTK_STAR_TX_THRESH))
> >  		netif_wake_queue(ndev);
> >  
> > -	spin_unlock(&priv->lock);
> > +	if (napi_complete(napi)) {
> > +		spin_lock_irqsave(&priv->lock, flags);
> > +		mtk_star_enable_dma_irq(priv, false, true);
> > +		spin_unlock_irqrestore(&priv->lock, flags);
> > +	}
> > +
> > +	return 0;
> >  }
> > @@ -1475,6 +1514,7 @@ static int mtk_star_set_timing(struct
> > mtk_star_priv *priv)
> >  
> >  	return regmap_write(priv->regs, MTK_STAR_REG_TEST0, delay_val);
> >  }
> > +
> >  static int mtk_star_probe(struct platform_device *pdev)
> >  {
> >  	struct device_node *of_node;
> 
> spurious whitespace change
Yes, will fix it in next send.

Best Regards!
Biao