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Commit 9a1654ba authored by Jarek Poplawski's avatar Jarek Poplawski Committed by David S. Miller
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net: Optimize hard_start_xmit() return checking 



Recent changes in the TX error propagation require additional checking
and masking of values returned from hard_start_xmit(), mainly to
separate cases where skb was consumed. This aim can be simplified by
changing the order of NETDEV_TX and NET_XMIT codes, because the latter
are treated similarly to negative (ERRNO) values.

After this change much simpler dev_xmit_complete() is also used in
sch_direct_xmit(), so it is moved to netdevice.h.

Additionally NET_RX definitions in netdevice.h are moved up from
between TX codes to avoid confusion while reading the TX comment.

Signed-off-by: default avatarJarek Poplawski <jarkao2@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent cb43e234

include/linux/netdevice.h

+30 −12
Original line number Diff line number Diff line
@@ -63,6 +63,10 @@ struct wireless_dev; 
#define HAVE_FREE_NETDEV		/* free_netdev() */

#define HAVE_NETDEV_PRIV		/* netdev_priv() */



/* Backlog congestion levels */

#define NET_RX_SUCCESS		0	/* keep 'em coming, baby */

#define NET_RX_DROP		1	/* packet dropped */



/*

 * Transmit return codes: transmit return codes originate from three different

 * namespaces:
@@ -82,14 +86,10 @@ struct wireless_dev; 


/* qdisc ->enqueue() return codes. */

#define NET_XMIT_SUCCESS	0x00

#define NET_XMIT_DROP		0x10	/* skb dropped			*/

#define NET_XMIT_CN		0x20	/* congestion notification	*/

#define NET_XMIT_POLICED	0x30	/* skb is shot by police	*/

#define NET_XMIT_MASK		0xf0	/* qdisc flags in net/sch_generic.h */



/* Backlog congestion levels */

#define NET_RX_SUCCESS		0	/* keep 'em coming, baby */

#define NET_RX_DROP		1	/* packet dropped */

#define NET_XMIT_DROP		0x01	/* skb dropped			*/

#define NET_XMIT_CN		0x02	/* congestion notification	*/

#define NET_XMIT_POLICED	0x03	/* skb is shot by police	*/

#define NET_XMIT_MASK		0x0f	/* qdisc flags in net/sch_generic.h */



/* NET_XMIT_CN is special. It does not guarantee that this packet is lost. It

 * indicates that the device will soon be dropping packets, or already drops
@@ -98,16 +98,34 @@ struct wireless_dev; 
#define net_xmit_errno(e)	((e) != NET_XMIT_CN ? -ENOBUFS : 0)



/* Driver transmit return codes */

#define NETDEV_TX_MASK		0xf

#define NETDEV_TX_MASK		0xf0



enum netdev_tx {

	__NETDEV_TX_MIN	 = INT_MIN,	/* make sure enum is signed */

	NETDEV_TX_OK	 = 0,		/* driver took care of packet */

	NETDEV_TX_BUSY	 = 1,		/* driver tx path was busy*/

	NETDEV_TX_LOCKED = 2,		/* driver tx lock was already taken */

	NETDEV_TX_OK	 = 0x00,	/* driver took care of packet */

	NETDEV_TX_BUSY	 = 0x10,	/* driver tx path was busy*/

	NETDEV_TX_LOCKED = 0x20,	/* driver tx lock was already taken */

};

typedef enum netdev_tx netdev_tx_t;



/*

 * Current order: NETDEV_TX_MASK > NET_XMIT_MASK >= 0 is significant;

 * hard_start_xmit() return < NET_XMIT_MASK means skb was consumed.

 */

static inline bool dev_xmit_complete(int rc)

{

	/*

	 * Positive cases with an skb consumed by a driver:

	 * - successful transmission (rc == NETDEV_TX_OK)

	 * - error while transmitting (rc < 0)

	 * - error while queueing to a different device (rc & NET_XMIT_MASK)

	 */

	if (likely(rc < NET_XMIT_MASK))

		return true;



	return false;

}



#endif



#define MAX_ADDR_LEN	32		/* Largest hardware address length */

net/core/dev.c

+0 −17
Original line number Diff line number Diff line
@@ -1924,23 +1924,6 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q, 
	return rc;

}



static inline bool dev_xmit_complete(int rc)

{

	/* successful transmission */

	if (rc == NETDEV_TX_OK)

		return true;



	/* error while transmitting, driver consumed skb */

	if (rc < 0)

		return true;



	/* error while queueing to a different device, driver consumed skb */

	if (rc & NET_XMIT_MASK)

		return true;



	return false;

}



/**

 *	dev_queue_xmit - transmit a buffer

 *	@skb: buffer to transmit

net/sched/sch_generic.c

+5 −18
Original line number Diff line number Diff line
@@ -119,39 +119,26 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q, 
	spin_unlock(root_lock);



	HARD_TX_LOCK(dev, txq, smp_processor_id());

	if (!netif_tx_queue_stopped(txq) &&

	    !netif_tx_queue_frozen(txq)) {

	if (!netif_tx_queue_stopped(txq) && !netif_tx_queue_frozen(txq))

		ret = dev_hard_start_xmit(skb, dev, txq);



		/* an error implies that the skb was consumed */

		if (ret < 0)

			ret = NETDEV_TX_OK;

		/* all NET_XMIT codes map to NETDEV_TX_OK */

		ret &= ~NET_XMIT_MASK;

	}

	HARD_TX_UNLOCK(dev, txq);



	spin_lock(root_lock);



	switch (ret) {

	case NETDEV_TX_OK:

		/* Driver sent out skb successfully */

	if (dev_xmit_complete(ret)) {

		/* Driver sent out skb successfully or skb was consumed */

		ret = qdisc_qlen(q);

		break;



	case NETDEV_TX_LOCKED:

	} else if (ret == NETDEV_TX_LOCKED) {

		/* Driver try lock failed */

		ret = handle_dev_cpu_collision(skb, txq, q);

		break;



	default:

	} else {

		/* Driver returned NETDEV_TX_BUSY - requeue skb */

		if (unlikely (ret != NETDEV_TX_BUSY && net_ratelimit()))

			printk(KERN_WARNING "BUG %s code %d qlen %d\n",

			       dev->name, ret, q->q.qlen);



		ret = dev_requeue_skb(skb, q);

		break;

	}



	if (ret && (netif_tx_queue_stopped(txq) ||