diff mbox series

[v3,14/16] can: m_can: Use tx_fifo_in_flight for netif_queue control

Message ID 20230315110546.2518305-15-msp@baylibre.com
State New
Headers
Series can: m_can: Optimizations for m_can/tcan part 2 |

Commit Message

Markus Schneider-Pargmann March 15, 2023, 11:05 a.m. UTC 
  The network queue is currently always stopped in start_xmit and
continued in the interrupt handler. This is not possible anymore if we
want to keep multiple transmits in flight in parallel.

Use the previously introduced tx_fifo_in_flight counter to control the
network queue instead. This has the benefit of not needing to ask the
hardware about fifo status.

This patch stops the network queue in start_xmit if the number of
transmits in flight reaches the size of the fifo and wakes up the queue
from the interrupt handler once the transmits in flight drops below the
fifo size. This means any skbs over the limit will be rejected
immediately in start_xmit (it shouldn't be possible at all to reach that
state anyways).

The maximum number of transmits in flight is the size of the fifo.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
---
 drivers/net/can/m_can/m_can.c | 71 +++++++++++++----------------------
 1 file changed, 26 insertions(+), 45 deletions(-)

Comments

Simon Horman March 17, 2023, 4:04 p.m. UTC | #1 
On Wed, Mar 15, 2023 at 12:05:44PM +0100, Markus Schneider-Pargmann wrote:
> The network queue is currently always stopped in start_xmit and
> continued in the interrupt handler. This is not possible anymore if we
> want to keep multiple transmits in flight in parallel.
> 
> Use the previously introduced tx_fifo_in_flight counter to control the
> network queue instead. This has the benefit of not needing to ask the
> hardware about fifo status.
> 
> This patch stops the network queue in start_xmit if the number of
> transmits in flight reaches the size of the fifo and wakes up the queue
> from the interrupt handler once the transmits in flight drops below the
> fifo size. This means any skbs over the limit will be rejected
> immediately in start_xmit (it shouldn't be possible at all to reach that
> state anyways).
> 
> The maximum number of transmits in flight is the size of the fifo.
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> ---
>  drivers/net/can/m_can/m_can.c | 71 +++++++++++++----------------------
>  1 file changed, 26 insertions(+), 45 deletions(-)
> 
> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> index 4ad8f08f8284..3cb3d01e1a61 100644
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/drivers/net/can/m_can/m_can.c

...

> @@ -1033,17 +1023,31 @@ static void m_can_finish_tx(struct m_can_classdev *cdev, int transmitted)
>  	unsigned long irqflags;
>  
>  	spin_lock_irqsave(&cdev->tx_handling_spinlock, irqflags);
> +	if (cdev->tx_fifo_in_flight >= cdev->tx_fifo_size && transmitted > 0)
> +		netif_wake_queue(cdev->net);
>  	cdev->tx_fifo_in_flight -= transmitted;
>  	spin_unlock_irqrestore(&cdev->tx_handling_spinlock, irqflags);
>  }
>  
> -static void m_can_start_tx(struct m_can_classdev *cdev)
> +static netdev_tx_t m_can_start_tx(struct m_can_classdev *cdev)
>  {
>  	unsigned long irqflags;
> +	int tx_fifo_in_flight;
>  
>  	spin_lock_irqsave(&cdev->tx_handling_spinlock, irqflags);
> -	++cdev->tx_fifo_in_flight;
> +	tx_fifo_in_flight = cdev->tx_fifo_in_flight + 1;
> +	if (tx_fifo_in_flight >= cdev->tx_fifo_size) {
> +		netif_stop_queue(cdev->net);
> +		if (tx_fifo_in_flight > cdev->tx_fifo_size) {
> +			netdev_err(cdev->net, "hard_xmit called while TX FIFO full\n");

Perhaps I misunderstand things.
But it seems that this message is triggered in the datapath.
Thus I think it should be rate limited, or perhaps only logged once.

> +			spin_unlock_irqrestore(&cdev->tx_handling_spinlock, irqflags);
> +			return NETDEV_TX_BUSY;
> +		}
> +	}
> +	cdev->tx_fifo_in_flight = tx_fifo_in_flight;
>  	spin_unlock_irqrestore(&cdev->tx_handling_spinlock, irqflags);
> +
> +	return NETDEV_TX_OK;
>  }
>  
>  static int m_can_echo_tx_event(struct net_device *dev)

...

> @@ -1830,11 +1810,6 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev,
>  		m_can_write(cdev, M_CAN_TXBAR, (1 << putidx));
>  		cdev->tx_fifo_putidx = (++cdev->tx_fifo_putidx >= cdev->can.echo_skb_max ?
>  					0 : cdev->tx_fifo_putidx);
> -
> -		/* stop network queue if fifo full */
> -		if (m_can_tx_fifo_full(cdev) ||
> -		    m_can_next_echo_skb_occupied(dev, putidx))
> -			netif_stop_queue(dev);
>  	}

smatch tells me that m_can_next_echo_skb_occupied is now defined but unused.

>  
>  	return NETDEV_TX_OK;

...
diff mbox series

Patch

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 4ad8f08f8284..3cb3d01e1a61 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -370,16 +370,6 @@  m_can_txe_fifo_read(struct m_can_classdev *cdev, u32 fgi, u32 offset, u32 *val)
 	return cdev->ops->read_fifo(cdev, addr_offset, val, 1);
 }
 
-static inline bool _m_can_tx_fifo_full(u32 txfqs)
-{
-	return !!(txfqs & TXFQS_TFQF);
-}
-
-static inline bool m_can_tx_fifo_full(struct m_can_classdev *cdev)
-{
-	return _m_can_tx_fifo_full(m_can_read(cdev, M_CAN_TXFQS));
-}
-
 static void m_can_config_endisable(struct m_can_classdev *cdev, bool enable)
 {
 	u32 cccr = m_can_read(cdev, M_CAN_CCCR);
@@ -1033,17 +1023,31 @@  static void m_can_finish_tx(struct m_can_classdev *cdev, int transmitted)
 	unsigned long irqflags;
 
 	spin_lock_irqsave(&cdev->tx_handling_spinlock, irqflags);
+	if (cdev->tx_fifo_in_flight >= cdev->tx_fifo_size && transmitted > 0)
+		netif_wake_queue(cdev->net);
 	cdev->tx_fifo_in_flight -= transmitted;
 	spin_unlock_irqrestore(&cdev->tx_handling_spinlock, irqflags);
 }
 
-static void m_can_start_tx(struct m_can_classdev *cdev)
+static netdev_tx_t m_can_start_tx(struct m_can_classdev *cdev)
 {
 	unsigned long irqflags;
+	int tx_fifo_in_flight;
 
 	spin_lock_irqsave(&cdev->tx_handling_spinlock, irqflags);
-	++cdev->tx_fifo_in_flight;
+	tx_fifo_in_flight = cdev->tx_fifo_in_flight + 1;
+	if (tx_fifo_in_flight >= cdev->tx_fifo_size) {
+		netif_stop_queue(cdev->net);
+		if (tx_fifo_in_flight > cdev->tx_fifo_size) {
+			netdev_err(cdev->net, "hard_xmit called while TX FIFO full\n");
+			spin_unlock_irqrestore(&cdev->tx_handling_spinlock, irqflags);
+			return NETDEV_TX_BUSY;
+		}
+	}
+	cdev->tx_fifo_in_flight = tx_fifo_in_flight;
 	spin_unlock_irqrestore(&cdev->tx_handling_spinlock, irqflags);
+
+	return NETDEV_TX_OK;
 }
 
 static int m_can_echo_tx_event(struct net_device *dev)
@@ -1187,7 +1191,6 @@  static irqreturn_t m_can_isr(int irq, void *dev_id)
 			if (cdev->is_peripheral)
 				timestamp = m_can_get_timestamp(cdev);
 			m_can_tx_update_stats(cdev, 0, timestamp);
-			netif_wake_queue(dev);
 			m_can_finish_tx(cdev, 1);
 		}
 	} else  {
@@ -1195,10 +1198,6 @@  static irqreturn_t m_can_isr(int irq, void *dev_id)
 			/* New TX FIFO Element arrived */
 			if (m_can_echo_tx_event(dev) != 0)
 				goto out_fail;
-
-			if (netif_queue_stopped(dev) &&
-			    !m_can_tx_fifo_full(cdev))
-				netif_wake_queue(dev);
 		}
 	}
 
@@ -1719,7 +1718,6 @@  static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev,
 	struct net_device *dev = cdev->net;
 	struct id_and_dlc fifo_header;
 	u32 cccr, fdflags;
-	u32 txfqs;
 	int err;
 	int putidx;
 
@@ -1776,24 +1774,6 @@  static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev,
 		u8 len_padded = DIV_ROUND_UP(cf->len, 4);
 		/* Transmit routine for version >= v3.1.x */
 
-		txfqs = m_can_read(cdev, M_CAN_TXFQS);
-
-		/* Check if FIFO full */
-		if (_m_can_tx_fifo_full(txfqs)) {
-			/* This shouldn't happen */
-			netif_stop_queue(dev);
-			netdev_warn(dev,
-				    "TX queue active although FIFO is full.");
-
-			if (cdev->is_peripheral) {
-				kfree_skb(skb);
-				dev->stats.tx_dropped++;
-				return NETDEV_TX_OK;
-			} else {
-				return NETDEV_TX_BUSY;
-			}
-		}
-
 		/* get put index for frame */
 		putidx = cdev->tx_fifo_putidx;
 
@@ -1830,11 +1810,6 @@  static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev,
 		m_can_write(cdev, M_CAN_TXBAR, (1 << putidx));
 		cdev->tx_fifo_putidx = (++cdev->tx_fifo_putidx >= cdev->can.echo_skb_max ?
 					0 : cdev->tx_fifo_putidx);
-
-		/* stop network queue if fifo full */
-		if (m_can_tx_fifo_full(cdev) ||
-		    m_can_next_echo_skb_occupied(dev, putidx))
-			netif_stop_queue(dev);
 	}
 
 	return NETDEV_TX_OK;
@@ -1868,14 +1843,16 @@  static void m_can_tx_queue_skb(struct m_can_classdev *cdev, struct sk_buff *skb)
 static netdev_tx_t m_can_start_peripheral_xmit(struct m_can_classdev *cdev,
 					       struct sk_buff *skb)
 {
+	netdev_tx_t err;
+
 	if (cdev->can.state == CAN_STATE_BUS_OFF) {
 		m_can_clean(cdev->net);
 		return NETDEV_TX_OK;
 	}
 
-	netif_stop_queue(cdev->net);
-
-	m_can_start_tx(cdev);
+	err = m_can_start_tx(cdev);
+	if (err != NETDEV_TX_OK)
+		return err;
 
 	m_can_tx_queue_skb(cdev, skb);
 
@@ -1885,7 +1862,11 @@  static netdev_tx_t m_can_start_peripheral_xmit(struct m_can_classdev *cdev,
 static netdev_tx_t m_can_start_fast_xmit(struct m_can_classdev *cdev,
 					 struct sk_buff *skb)
 {
-	m_can_start_tx(cdev);
+	netdev_tx_t err;
+
+	err = m_can_start_tx(cdev);
+	if (err != NETDEV_TX_OK)
+		return err;
 
 	return m_can_tx_handler(cdev, skb);
 }