Date:	Mon, 15 Dec 2014 14:29:45 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Ding Tianhong <dingtianhong@...wei.com>, zhangfei.gao@...aro.org,
	davem@...emloft.net, linux@....linux.org.uk, f.fainelli@...il.com,
	sergei.shtylyov@...entembedded.com, mark.rutland@....com,
	David.Laight@...lab.com, eric.dumazet@...il.com,
	xuwei5@...ilicon.com, netdev@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH net-next v9 0/3] add hisilicon hip04 ethernet driver

On Thursday 11 December 2014 19:42:27 Ding Tianhong wrote:
> v9:
> - There is no tx completion interrupts to free DMAd Tx packets, it means taht
>   we rely on new tx packets arriving to run the destructors of completed packets,
>   which open up space in their sockets's send queues. Sometimes we don't get such
>   new packets causing Tx to stall, a single UDP transmitter is a good example of
>   this situation, so we need a clean up workqueue to reclaims completed packets,
>   the workqueue will only free the last packets which is already stay for several jiffies.
>   Also fix some format cleanups.

You must have missed the reply in which David Miller explained why
you can't call skb_orphan and rely on an occasional cleanup of the
queue. Please use something like the patch below:

- drop the broken skb_orphan call
- drop the workqueue
- batch cleanup based on tx_coalesce_frames/usecs for better throughput
- use a reasonable default tx timeout (200us, could be shorted
  based on measurements) with a range timer
- fix napi poll function return value
- use a lockless queue for cleanup

Signed-off-by: Arnd Bergmann <arnd@...db.de>

Feel free to fold this into your patch rather than keeping it separate.
Completely untested, probably contains some bugs. Please ask if you
have questions about this.

diff --git a/drivers/net/ethernet/hisilicon/hip04_eth.c b/drivers/net/ethernet/hisilicon/hip04_eth.c
index 9d37b670db6a..d85c5287654e 100644
--- a/drivers/net/ethernet/hisilicon/hip04_eth.c
+++ b/drivers/net/ethernet/hisilicon/hip04_eth.c
@@ -12,6 +12,7 @@
 #include <linux/etherdevice.h>
 #include <linux/platform_device.h>
 #include <linux/interrupt.h>
+#include <linux/ktime.h>
 #include <linux/of_address.h>
 #include <linux/phy.h>
 #include <linux/of_mdio.h>
@@ -157,9 +158,11 @@ struct hip04_priv {
 	struct sk_buff *tx_skb[TX_DESC_NUM];
 	dma_addr_t tx_phys[TX_DESC_NUM];
 	unsigned int tx_head;
-	unsigned int tx_tail;
-	int tx_count;
-	unsigned long last_tx;
+
+	/* FIXME: make these adjustable through ethtool */
+	int tx_coalesce_frames;
+	int tx_coalesce_usecs;
+	struct hrtimer tx_coalesce_timer;
 
 	unsigned char *rx_buf[RX_DESC_NUM];
 	dma_addr_t rx_phys[RX_DESC_NUM];
@@ -171,10 +174,15 @@ struct hip04_priv {
 	struct regmap *map;
 	struct work_struct tx_timeout_task;
 
-	struct workqueue_struct *wq;
-	struct delayed_work tx_clean_task;
+	/* written only by tx cleanup */
+	unsigned int tx_tail ____cacheline_aligned_in_smp;
 };
 
+static inline unsigned int tx_count(unsigned int head, unsigned int tail)
+{
+	return (head - tail) % (TX_DESC_NUM - 1);
+}
+
 static void hip04_config_port(struct net_device *ndev, u32 speed, u32 duplex)
 {
 	struct hip04_priv *priv = netdev_priv(ndev);
@@ -351,18 +359,21 @@ static int hip04_set_mac_address(struct net_device *ndev, void *addr)
 	return 0;
 }
 
-static void hip04_tx_reclaim(struct net_device *ndev, bool force)
+static int hip04_tx_reclaim(struct net_device *ndev, bool force)
 {
 	struct hip04_priv *priv = netdev_priv(ndev);
 	unsigned tx_tail = priv->tx_tail;
 	struct tx_desc *desc;
 	unsigned int bytes_compl = 0, pkts_compl = 0;
+	unsigned int count;
 
-	if (priv->tx_count == 0)
+	smp_rmb();
+	count = tx_count(ACCESS_ONCE(priv->tx_head), tx_tail);
+	if (count == 0)
 		goto out;
 
-	while ((tx_tail != priv->tx_head) || (priv->tx_count == TX_DESC_NUM)) {
-		desc = &priv->tx_desc[priv->tx_tail];
+	while (count) {
+		desc = &priv->tx_desc[tx_tail];
 		if (desc->send_addr != 0) {
 			if (force)
 				desc->send_addr = 0;
@@ -381,57 +392,37 @@ static void hip04_tx_reclaim(struct net_device *ndev, bool force)
 		dev_kfree_skb(priv->tx_skb[tx_tail]);
 		priv->tx_skb[tx_tail] = NULL;
 		tx_tail = TX_NEXT(tx_tail);
-		priv->tx_count--;
-
-		if (priv->tx_count <= 0)
-			break;
+		count--;
 	}
 
 	priv->tx_tail = tx_tail;
+	smp_wmb(); /* Ensure tx_tail visible to xmit */
 
-	/* Ensure tx_tail & tx_count visible to xmit */
-	smp_mb();
 out:
-
 	if (pkts_compl || bytes_compl)
 		netdev_completed_queue(ndev, pkts_compl, bytes_compl);
 
-	if (unlikely(netif_queue_stopped(ndev)) &&
-	    (priv->tx_count < TX_DESC_NUM))
+	if (unlikely(netif_queue_stopped(ndev)) && (count < (TX_DESC_NUM - 1)))
 		netif_wake_queue(ndev);
-}
 
-static void hip04_tx_clean_monitor(struct work_struct *work)
-{
-	struct hip04_priv *priv = container_of(work, struct hip04_priv,
-					       tx_clean_task.work);
-	struct net_device *ndev = priv->ndev;
-	int delta_in_ticks = msecs_to_jiffies(1000);
-
-	if (!time_in_range(jiffies, priv->last_tx,
-			   priv->last_tx + delta_in_ticks)) {
-		netif_tx_lock(ndev);
-		hip04_tx_reclaim(ndev, false);
-		netif_tx_unlock(ndev);
-	}
-	queue_delayed_work(priv->wq, &priv->tx_clean_task, delta_in_ticks);
+	return count;
 }
 
 static int hip04_mac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
 	struct hip04_priv *priv = netdev_priv(ndev);
 	struct net_device_stats *stats = &ndev->stats;
-	unsigned int tx_head = priv->tx_head;
+	unsigned int tx_head = priv->tx_head, count;
 	struct tx_desc *desc = &priv->tx_desc[tx_head];
 	dma_addr_t phys;
 
-	if (priv->tx_count >= TX_DESC_NUM) {
+	smp_rmb();
+	count = tx_count(tx_head, ACCESS_ONCE(priv->tx_tail));
+	if (count == (TX_DESC_NUM - 1)) {
 		netif_stop_queue(ndev);
 		return NETDEV_TX_BUSY;
 	}
 
-	hip04_tx_reclaim(ndev, false);
-
 	phys = dma_map_single(&ndev->dev, skb->data, skb->len, DMA_TO_DEVICE);
 	if (dma_mapping_error(&ndev->dev, phys)) {
 		dev_kfree_skb(skb);
@@ -447,20 +438,33 @@ static int hip04_mac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	desc->wb_addr = cpu_to_be32(phys);
 	skb_tx_timestamp(skb);
 
-	/* Don't wait up for transmitted skbs to be freed. */
-	skb_orphan(skb);
-
+	/* FIXME: eliminate this mmio access if xmit_more is set */
 	hip04_set_xmit_desc(priv, phys);
 	priv->tx_head = TX_NEXT(tx_head);
+	count++;
 	netdev_sent_queue(ndev, skb->len);
 
 	stats->tx_bytes += skb->len;
 	stats->tx_packets++;
-	priv->tx_count++;
-	priv->last_tx = jiffies;
 
-	/* Ensure tx_head & tx_count update visible to tx reclaim */
-	smp_mb();
+	/* Ensure tx_head update visible to tx reclaim */
+	smp_wmb();
+
+	/* queue is getting full, better start cleaning up now */
+	if (count >= priv->tx_coalesce_frames) {
+		if (napi_schedule_prep(&priv->napi)) {
+			/* disable rx interrupt and timer */
+			priv->reg_inten &= ~(RCV_INT);
+			writel_relaxed(DEF_INT_MASK & ~RCV_INT,
+				       priv->base + PPE_INTEN);
+			hrtimer_cancel(&priv->tx_coalesce_timer);
+			__napi_schedule(&priv->napi);
+		}
+	} else if (!hrtimer_is_queued(&priv->tx_coalesce_timer)) {
+		/* cleanup not pending yet, start a new timer */
+		hrtimer_start_expires(&priv->tx_coalesce_timer,
+				      HRTIMER_MODE_REL);
+	}
 
 	return NETDEV_TX_OK;
 }
@@ -477,6 +481,7 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
 	bool last = false;
 	dma_addr_t phys;
 	int rx = 0;
+	int tx_remaining;
 	u16 len;
 	u32 err;
 
@@ -513,11 +518,11 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
 
 		buf = netdev_alloc_frag(priv->rx_buf_size);
 		if (!buf)
-			return -ENOMEM;
+			goto done;
 		phys = dma_map_single(&ndev->dev, buf,
 				      RX_BUF_SIZE, DMA_FROM_DEVICE);
 		if (dma_mapping_error(&ndev->dev, phys))
-			return -EIO;
+			goto done;
 		priv->rx_buf[priv->rx_head] = buf;
 		priv->rx_phys[priv->rx_head] = phys;
 		hip04_set_recv_desc(priv, phys);
@@ -537,6 +542,11 @@ static int hip04_rx_poll(struct napi_struct *napi, int budget)
 	}
 	napi_complete(napi);
 done:
+	/* clean up tx descriptors and start a new timer if necessary */
+	tx_remaining = hip04_tx_reclaim(ndev, false);
+	if (rx < budget && tx_remaining)
+		hrtimer_start_expires(&priv->tx_coalesce_timer, HRTIMER_MODE_REL);
+
 	return rx;
 }
 
@@ -547,6 +557,9 @@ static irqreturn_t hip04_mac_interrupt(int irq, void *dev_id)
 	struct net_device_stats *stats = &ndev->stats;
 	u32 ists = readl_relaxed(priv->base + PPE_INTSTS);
 
+	if (!ists)
+		return IRQ_NONE;
+
 	writel_relaxed(DEF_INT_MASK, priv->base + PPE_RINT);
 
 	if (unlikely(ists & DEF_INT_ERR)) {
@@ -560,16 +573,32 @@ static irqreturn_t hip04_mac_interrupt(int irq, void *dev_id)
 		}
 	}
 
-	if (ists & RCV_INT) {
+	if (ists & RCV_INT && napi_schedule_prep(&priv->napi)) {
 		/* disable rx interrupt */
 		priv->reg_inten &= ~(RCV_INT);
-		writel_relaxed(priv->reg_inten, priv->base + PPE_INTEN);
-		napi_schedule(&priv->napi);
+		writel_relaxed(DEF_INT_MASK & ~RCV_INT, priv->base + PPE_INTEN);
+		hrtimer_cancel(&priv->tx_coalesce_timer);
+		__napi_schedule(&priv->napi);
 	}
 
 	return IRQ_HANDLED;
 }
 
+enum hrtimer_restart tx_done(struct hrtimer *hrtimer)
+{
+	struct hip04_priv *priv;
+	priv = container_of(hrtimer, struct hip04_priv, tx_coalesce_timer);
+
+	if (napi_schedule_prep(&priv->napi)) {
+		/* disable rx interrupt */
+		priv->reg_inten &= ~(RCV_INT);
+		writel_relaxed(DEF_INT_MASK & ~RCV_INT, priv->base + PPE_INTEN);
+		__napi_schedule(&priv->napi);
+	}
+
+	return HRTIMER_NORESTART;
+}
+
 static void hip04_adjust_link(struct net_device *ndev)
 {
 	struct hip04_priv *priv = netdev_priv(ndev);
@@ -589,7 +618,6 @@ static int hip04_mac_open(struct net_device *ndev)
 	priv->rx_head = 0;
 	priv->tx_head = 0;
 	priv->tx_tail = 0;
-	priv->tx_count = 0;
 	hip04_reset_ppe(priv);
 
 	for (i = 0; i < RX_DESC_NUM; i++) {
@@ -612,9 +640,6 @@ static int hip04_mac_open(struct net_device *ndev)
 	hip04_mac_enable(ndev);
 	napi_enable(&priv->napi);
 
-	INIT_DELAYED_WORK(&priv->tx_clean_task, hip04_tx_clean_monitor);
-	queue_delayed_work(priv->wq, &priv->tx_clean_task, 0);
-
 	return 0;
 }
 
@@ -623,8 +648,6 @@ static int hip04_mac_stop(struct net_device *ndev)
 	struct hip04_priv *priv = netdev_priv(ndev);
 	int i;
 
-	cancel_delayed_work_sync(&priv->tx_clean_task);
-
 	napi_disable(&priv->napi);
 	netif_stop_queue(ndev);
 	hip04_mac_disable(ndev);
@@ -725,6 +748,7 @@ static int hip04_mac_probe(struct platform_device *pdev)
 	struct hip04_priv *priv;
 	struct resource *res;
 	unsigned int irq;
+	ktime_t txtime;
 	int ret;
 
 	ndev = alloc_etherdev(sizeof(struct hip04_priv));
@@ -751,6 +775,21 @@ static int hip04_mac_probe(struct platform_device *pdev)
 	priv->port = arg.args[0];
 	priv->chan = arg.args[1] * RX_DESC_NUM;
 
+	hrtimer_init(&priv->tx_coalesce_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+
+	/*
+	 * BQL will try to keep the TX queue as short as possible, but it can't
+	 * be faster than tx_coalesce_usecs, so we need a fast timeout here,
+	 * but also long enough to gather up enough frames to ensure we don't
+	 * get more interrupts than necessary.
+	 * 200us is enough for 16 frames of 1500 bytes at gigabit ethernet rate
+	 */
+	priv->tx_coalesce_frames = TX_DESC_NUM * 3 / 4;
+	priv->tx_coalesce_usecs = 200;
+	/* allow timer to fire after half the time at the earliest */
+	txtime = ktime_set(0, priv->tx_coalesce_usecs * NSEC_PER_USEC / 2);
+	hrtimer_set_expires_range(&priv->tx_coalesce_timer, txtime, txtime);
+
 	priv->map = syscon_node_to_regmap(arg.np);
 	if (IS_ERR(priv->map)) {
 		dev_warn(d, "no syscon hisilicon,hip04-ppe\n");
@@ -788,12 +827,6 @@ static int hip04_mac_probe(struct platform_device *pdev)
 		}
 	}
 
-	priv->wq = create_singlethread_workqueue(ndev->name);
-	if (!priv->wq) {
-		ret = -ENOMEM;
-		goto init_fail;
-	}
-
 	INIT_WORK(&priv->tx_timeout_task, hip04_tx_timeout_task);
 
 	ether_setup(ndev);
@@ -848,8 +881,6 @@ static int hip04_remove(struct platform_device *pdev)
 	free_irq(ndev->irq, ndev);
 	of_node_put(priv->phy_node);
 	cancel_work_sync(&priv->tx_timeout_task);
-	if (priv->wq)
-		destroy_workqueue(priv->wq);
 	free_netdev(ndev);
 
 	return 0;

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