[PATCH] Add NETIF_F_LLTX to e1000 driver

[Andi Kleen <ak@xxxxxx>]

This patch adds NETIF_F_LLTX to the e1000 driver.  With this
the driver can take one lock less in the TX path.

It will do a try lock on the tx_lock now and bail out when the lock is
already locked. I extended the use of tx_lock a bit to protect some
data structures that were previously only protected by the xmit_lock.
I also added taking of tx_lock to the set_multicast_list to
prevent any potential races here.

It requires the lltx patch I sent before to netdev applied first.

-Andi

diff -u linux-2.6.8-work/drivers/net/e1000/e1000_main.c-o 
linux-2.6.8-work/drivers/net/e1000/e1000_main.c
--- linux-2.6.8-work/drivers/net/e1000/e1000_main.c-o   2004-07-27 
14:44:07.000000000 +0200
+++ linux-2.6.8-work/drivers/net/e1000/e1000_main.c     2004-08-31 
14:43:43.000000000 +0200
@@ -486,6 +486,9 @@
 #endif
 #endif
 
+       /* hard_start_xmit is safe against parallel locking */
+       netdev->features |= NETIF_F_LLTX; 
+
        if(pci_using_dac)
                netdev->features |= NETIF_F_HIGHDMA;
 
@@ -1259,9 +1262,12 @@
        uint32_t rctl;
        uint32_t hash_value;
        int i;
+       unsigned long flags;
 
        /* Check for Promiscuous and All Multicast modes */
 
+       spin_lock_irqsave(&adapter->tx_lock, flags);
+
        rctl = E1000_READ_REG(hw, RCTL);
 
        if(netdev->flags & IFF_PROMISC) {
@@ -1310,6 +1316,8 @@
 
        if(hw->mac_type == e1000_82542_rev2_0)
                e1000_leave_82542_rst(adapter);
+
+       spin_unlock_irqrestore(&adapter->tx_lock, flags);
 }
 
 /* need to wait a few seconds after link up to get diagnostic information from 
the phy */
@@ -1785,7 +1793,13 @@
        if(adapter->pcix_82544)
                count += nr_frags;
        
-       spin_lock_irqsave(&adapter->tx_lock, flags);
+       local_irq_save(flags); 
+       if (!spin_trylock(&adapter->tx_lock)) { 
+               /* Collision - tell upper layer to requeue */ 
+               local_irq_restore(flags); 
+               return -1; 
+       } 
+
        /* need: count +  2 desc gap to keep tail from touching 
         * head, otherwise try next time */
        if(E1000_DESC_UNUSED(&adapter->tx_ring) < count + 2 ) {
@@ -1793,11 +1807,11 @@
                spin_unlock_irqrestore(&adapter->tx_lock, flags);
                return 1;
        }
-       spin_unlock_irqrestore(&adapter->tx_lock, flags);
 
        if(adapter->hw.mac_type == e1000_82547) {
                if(e1000_82547_fifo_workaround(adapter, skb)) {
                        netif_stop_queue(netdev);
+                       spin_unlock_irqrestore(&adapter->tx_lock, flags);
                        mod_timer(&adapter->tx_fifo_stall_timer, jiffies);
                        return 1;
                }
@@ -1821,6 +1835,7 @@
 
        netdev->trans_start = jiffies;
 
+       spin_unlock_irqrestore(&adapter->tx_lock, flags);
        return 0;
 }