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: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 35 insertions, 47 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 61425d0c6123..7043f85e643d 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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 */
diff --git a/net/core/dev.c b/net/core/dev.c
index 32045df1da5c..4b24d79414e3 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -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
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index b13821ad2fb6..5173c1e1b19c 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -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) ||