firewire: net: throttle TX queue before running out of tlabels

This prevents firewire-net from submitting write requests in fast
succession until failure due to all 64 transaction labels were used up
for unfinished split transactions.  The netif_stop/wake_queue API is
used for this purpose.

Without this stop/wake mechanism, datagrams were simply lost whenever
the tlabel pool was exhausted.  Plus, tlabel exhaustion by firewire-net
also prevented other unrelated outbound transactions to be initiated.

The chosen queue depth was checked by me to hit the maximum possible
throughput with an OS X peer whose receive DMA is good enough to never
reject requests due to busy inbound request FIFO.  Current Linux peers
show a mixed picture of -5%...+15% change in bandwidth; their current
bottleneck are RCODE_BUSY situations (fewer or more, depending on TX
queue depth) due to too small AR buffer in firewire-ohci.

Maxim Levitsky tested this change with similar watermarks with a Linux
peer and some pending firewire-ohci improvements that address the
RCODE_BUSY problem and confirmed that these TX queue limits are good.

Note:  This removes some netif_wake_queue from reception code paths.
They were apparently copy&paste artefacts from a nonsensical
netif_wake_queue use in the older eth1394 driver.  This belongs only
into the transmit path.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Tested-by: Maxim Levitsky <maximlevitsky@gmail.com>

1 files changed, 35 insertions, 24 deletions

diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
index d2d488b9cd9..1a467a91fb0 100644
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -27,8 +27,14 @@
 #include <asm/unaligned.h>
 #include <net/arp.h>
 
-#define FWNET_MAX_FRAGMENTS     25      /* arbitrary limit */
-#define FWNET_ISO_PAGE_COUNT    (PAGE_SIZE < 16 * 1024 ? 4 : 2)
+/* rx limits */
+#define FWNET_MAX_FRAGMENTS             30 /* arbitrary, > TX queue depth */
+#define FWNET_ISO_PAGE_COUNT            (PAGE_SIZE < 16*1024 ? 4 : 2)
+
+/* tx limits */
+#define FWNET_MAX_QUEUED_DATAGRAMS      20 /* < 64 = number of tlabels */
+#define FWNET_MIN_QUEUED_DATAGRAMS      10 /* should keep AT DMA busy enough */
+#define FWNET_TX_QUEUE_LEN              FWNET_MAX_QUEUED_DATAGRAMS /* ? */
 
 #define IEEE1394_BROADCAST_CHANNEL      31
 #define IEEE1394_ALL_NODES              (0xffc0 | 0x003f)
@@ -640,8 +646,6 @@ static int fwnet_finish_incoming_packet(struct net_device *net,
                 net->stats.rx_packets++;
                 net->stats.rx_bytes += skb->len;
         }
-        if (netif_queue_stopped(net))
-                netif_wake_queue(net);
 
         return 0;
 
@@ -650,8 +654,6 @@ static int fwnet_finish_incoming_packet(struct net_device *net,
         net->stats.rx_dropped++;
 
         dev_kfree_skb_any(skb);
-        if (netif_queue_stopped(net))
-                netif_wake_queue(net);
 
         return -ENOENT;
 }
@@ -783,15 +785,10 @@ static int fwnet_incoming_packet(struct fwnet_device *dev, __be32 *buf, int len,
          * Datagram is not complete, we're done for the
          * moment.
          */
-        spin_unlock_irqrestore(&dev->lock, flags);
-
-        return 0;
+        retval = 0;
  fail:
         spin_unlock_irqrestore(&dev->lock, flags);
 
-        if (netif_queue_stopped(net))
-                netif_wake_queue(net);
-
         return retval;
 }
 
@@ -891,6 +888,13 @@ static void fwnet_free_ptask(struct fwnet_packet_task *ptask)
         kmem_cache_free(fwnet_packet_task_cache, ptask);
 }
 
+/* Caller must hold dev->lock. */
+static void dec_queued_datagrams(struct fwnet_device *dev)
+{
+        if (--dev->queued_datagrams == FWNET_MIN_QUEUED_DATAGRAMS)
+                netif_wake_queue(dev->netdev);
+}
+
 static int fwnet_send_packet(struct fwnet_packet_task *ptask);
 
 static void fwnet_transmit_packet_done(struct fwnet_packet_task *ptask)
@@ -907,7 +911,7 @@ static void fwnet_transmit_packet_done(struct fwnet_packet_task *ptask)
         /* Check whether we or the networking TX soft-IRQ is last user. */
         free = (ptask->outstanding_pkts == 0 && ptask->enqueued);
         if (free)
-                dev->queued_datagrams--;
+                dec_queued_datagrams(dev);
 
         if (ptask->outstanding_pkts == 0) {
                 dev->netdev->stats.tx_packets++;
@@ -978,7 +982,7 @@ static void fwnet_transmit_packet_failed(struct fwnet_packet_task *ptask)
         /* Check whether we or the networking TX soft-IRQ is last user. */
         free = ptask->enqueued;
         if (free)
-                dev->queued_datagrams--;
+                dec_queued_datagrams(dev);
 
         dev->netdev->stats.tx_dropped++;
         dev->netdev->stats.tx_errors++;
@@ -1063,7 +1067,7 @@ static int fwnet_send_packet(struct fwnet_packet_task *ptask)
                 if (!free)
                         ptask->enqueued = true;
                 else
-                        dev->queued_datagrams--;
+                        dec_queued_datagrams(dev);
 
                 spin_unlock_irqrestore(&dev->lock, flags);
 
@@ -1082,7 +1086,7 @@ static int fwnet_send_packet(struct fwnet_packet_task *ptask)
         if (!free)
                 ptask->enqueued = true;
         else
-                dev->queued_datagrams--;
+                dec_queued_datagrams(dev);
 
         spin_unlock_irqrestore(&dev->lock, flags);
 
@@ -1248,6 +1252,15 @@ static netdev_tx_t fwnet_tx(struct sk_buff *skb, struct net_device *net)
         struct fwnet_peer *peer;
         unsigned long flags;
 
+        spin_lock_irqsave(&dev->lock, flags);
+
+        /* Can this happen? */
+        if (netif_queue_stopped(dev->netdev)) {
+                spin_unlock_irqrestore(&dev->lock, flags);
+
+                return NETDEV_TX_BUSY;
+        }
+
         ptask = kmem_cache_alloc(fwnet_packet_task_cache, GFP_ATOMIC);
         if (ptask == NULL)
                 goto fail;
@@ -1266,9 +1279,6 @@ static netdev_tx_t fwnet_tx(struct sk_buff *skb, struct net_device *net)
         proto = hdr_buf.h_proto;
         dg_size = skb->len;
 
-        /* serialize access to peer, including peer->datagram_label */
-        spin_lock_irqsave(&dev->lock, flags);
-
         /*
          * Set the transmission type for the packet.  ARP packets and IP
          * broadcast packets are sent via GASP.
@@ -1290,7 +1300,7 @@ static netdev_tx_t fwnet_tx(struct sk_buff *skb, struct net_device *net)
 
                 peer = fwnet_peer_find_by_guid(dev, be64_to_cpu(guid));
                 if (!peer || peer->fifo == FWNET_NO_FIFO_ADDR)
-                        goto fail_unlock;
+                        goto fail;
 
                 generation         = peer->generation;
                 dest_node          = peer->node_id;
@@ -1344,7 +1354,8 @@ static netdev_tx_t fwnet_tx(struct sk_buff *skb, struct net_device *net)
                 max_payload += RFC2374_FRAG_HDR_SIZE;
         }
 
-        dev->queued_datagrams++;
+        if (++dev->queued_datagrams == FWNET_MAX_QUEUED_DATAGRAMS)
+                netif_stop_queue(dev->netdev);
 
         spin_unlock_irqrestore(&dev->lock, flags);
 
@@ -1355,9 +1366,9 @@ static netdev_tx_t fwnet_tx(struct sk_buff *skb, struct net_device *net)
 
         return NETDEV_TX_OK;
 
- fail_unlock:
-        spin_unlock_irqrestore(&dev->lock, flags);
  fail:
+        spin_unlock_irqrestore(&dev->lock, flags);
+
         if (ptask)
                 kmem_cache_free(fwnet_packet_task_cache, ptask);
 
@@ -1403,7 +1414,7 @@ static void fwnet_init_dev(struct net_device *net)
         net->addr_len           = FWNET_ALEN;
         net->hard_header_len    = FWNET_HLEN;
         net->type               = ARPHRD_IEEE1394;
-        net->tx_queue_len       = 10;
+        net->tx_queue_len       = FWNET_TX_QUEUE_LEN;
 }
 
 /* caller must hold fwnet_device_mutex */