[PATCH] powerpc/cell spidernet refine locking

The transmit side of the spider ethernet driver currently
places locks around some very large chunks of code. This
results in a fair amount of lock contention is some cases.
This patch makes the locks much more fine-grained, protecting
only the cirtical sections. One lock is used to protect
three locations: the queue head and tail pointers, and the
queue low-watermark location.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: James K Lewis <jklewis@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/net/spider_net.c b/drivers/net/spider_net.c
index e429abc1e947c1663194fa368f73313cd2fb755d..f8d7d0d91a6dca9251bbb2a256408924d4b9005c 100644 (file)
--- a/drivers/net/spider_net.c
+++ b/drivers/net/spider_net.c
@@ -646,8 +646,9 @@ static int
 spider_net_prepare_tx_descr(struct spider_net_card *card,
                            struct sk_buff *skb)
 {
-       struct spider_net_descr *descr = card->tx_chain.head;
+       struct spider_net_descr *descr;
        dma_addr_t buf;
+       unsigned long flags;
        int length;
 
        length = skb->len;
@@ -666,6 +667,10 @@ spider_net_prepare_tx_descr(struct spider_net_card *card,
                return -ENOMEM;
        }
 
+       spin_lock_irqsave(&card->tx_chain.lock, flags);
+       descr = card->tx_chain.head;
+       card->tx_chain.head = descr->next;
+
        descr->buf_addr = buf;
        descr->buf_size = length;
        descr->next_descr_addr = 0;
@@ -674,6 +679,8 @@ spider_net_prepare_tx_descr(struct spider_net_card *card,
 
        descr->dmac_cmd_status =
                        SPIDER_NET_DESCR_CARDOWNED | SPIDER_NET_DMAC_NOCS;
+       spin_unlock_irqrestore(&card->tx_chain.lock, flags);
+
        if (skb->protocol == htons(ETH_P_IP))
                switch (skb->nh.iph->protocol) {
                case IPPROTO_TCP:
@@ -691,42 +698,17 @@ spider_net_prepare_tx_descr(struct spider_net_card *card,
        return 0;
 }
 
-/**
- * spider_net_release_tx_descr - processes a used tx descriptor
- * @card: card structure
- * @descr: descriptor to release
- *
- * releases a used tx descriptor (unmapping, freeing of skb)
- */
-static inline void
-spider_net_release_tx_descr(struct spider_net_card *card)
-{
-       struct spider_net_descr *descr = card->tx_chain.tail;
-       struct sk_buff *skb;
-       unsigned int len;
-
-       card->tx_chain.tail = card->tx_chain.tail->next;
-       descr->dmac_cmd_status |= SPIDER_NET_DESCR_NOT_IN_USE;
-
-       /* unmap the skb */
-       skb = descr->skb;
-       if (!skb)
-               return;
-       len = skb->len < ETH_ZLEN ? ETH_ZLEN : skb->len;
-       pci_unmap_single(card->pdev, descr->buf_addr, len,
-                       PCI_DMA_TODEVICE);
-       dev_kfree_skb(skb);
-}
-
 static void
 spider_net_set_low_watermark(struct spider_net_card *card)
 {
+       unsigned long flags;
        int status;
        int cnt=0;
        int i;
        struct spider_net_descr *descr = card->tx_chain.tail;
 
-       /* Measure the length of the queue. */
+       /* Measure the length of the queue. Measurement does not
+        * need to be precise -- does not need a lock. */
        while (descr != card->tx_chain.head) {
                status = descr->dmac_cmd_status & SPIDER_NET_DESCR_NOT_IN_USE;
                if (status == SPIDER_NET_DESCR_NOT_IN_USE)
@@ -746,11 +728,13 @@ spider_net_set_low_watermark(struct spider_net_card *card)
                descr = descr->next;
 
        /* Set the new watermark, clear the old watermark */
+       spin_lock_irqsave(&card->tx_chain.lock, flags);
        descr->dmac_cmd_status |= SPIDER_NET_DESCR_TXDESFLG;
        if (card->low_watermark && card->low_watermark != descr)
                card->low_watermark->dmac_cmd_status =
                     card->low_watermark->dmac_cmd_status & ~SPIDER_NET_DESCR_TXDESFLG;
        card->low_watermark = descr;
+       spin_unlock_irqrestore(&card->tx_chain.lock, flags);
 }
 
 /**
@@ -769,21 +753,31 @@ static int
 spider_net_release_tx_chain(struct spider_net_card *card, int brutal)
 {
        struct spider_net_descr_chain *chain = &card->tx_chain;
+       struct spider_net_descr *descr;
+       struct sk_buff *skb;
+       u32 buf_addr;
+       unsigned long flags;
        int status;
 
        spider_net_read_reg(card, SPIDER_NET_GDTDMACCNTR);
 
        while (chain->tail != chain->head) {
-               status = spider_net_get_descr_status(chain->tail);
+               spin_lock_irqsave(&chain->lock, flags);
+               descr = chain->tail;
+
+               status = spider_net_get_descr_status(descr);
                switch (status) {
                case SPIDER_NET_DESCR_COMPLETE:
                        card->netdev_stats.tx_packets++;
-                       card->netdev_stats.tx_bytes += chain->tail->skb->len;
+                       card->netdev_stats.tx_bytes += descr->skb->len;
                        break;
 
                case SPIDER_NET_DESCR_CARDOWNED:
-                       if (!brutal)
+                       if (!brutal) {
+                               spin_unlock_irqrestore(&chain->lock, flags);
                                return 1;
+                       }
+
                        /* fallthrough, if we release the descriptors
                         * brutally (then we don't care about
                         * SPIDER_NET_DESCR_CARDOWNED) */
@@ -800,12 +794,25 @@ spider_net_release_tx_chain(struct spider_net_card *card, int brutal)
 
                default:
                        card->netdev_stats.tx_dropped++;
-                       if (!brutal)
+                       if (!brutal) {
+                               spin_unlock_irqrestore(&chain->lock, flags);
                                return 1;
+                       }
                }
-               spider_net_release_tx_descr(card);
-       }
 
+               chain->tail = descr->next;
+               descr->dmac_cmd_status |= SPIDER_NET_DESCR_NOT_IN_USE;
+               skb = descr->skb;
+               buf_addr = descr->buf_addr;
+               spin_unlock_irqrestore(&chain->lock, flags);
+
+               /* unmap the skb */
+               if (skb) {
+                       int len = skb->len < ETH_ZLEN ? ETH_ZLEN : skb->len;
+                       pci_unmap_single(card->pdev, buf_addr, len, PCI_DMA_TODEVICE);
+                       dev_kfree_skb(skb);
+               }
+       }
        return 0;
 }
 
@@ -857,27 +864,19 @@ spider_net_xmit(struct sk_buff *skb, struct net_device *netdev)
 {
        struct spider_net_card *card = netdev_priv(netdev);
        struct spider_net_descr_chain *chain = &card->tx_chain;
-       struct spider_net_descr *descr = chain->head;
-       unsigned long flags;
-
-       spin_lock_irqsave(&chain->lock, flags);
 
        spider_net_release_tx_chain(card, 0);
 
        if ((chain->head->next == chain->tail->prev) ||
-          (spider_net_get_descr_status(descr) != SPIDER_NET_DESCR_NOT_IN_USE) ||
           (spider_net_prepare_tx_descr(card, skb) != 0)) {
 
                card->netdev_stats.tx_dropped++;
-               spin_unlock_irqrestore(&chain->lock, flags);
                netif_stop_queue(netdev);
                return NETDEV_TX_BUSY;
        }
 
        spider_net_set_low_watermark(card);
        spider_net_kick_tx_dma(card);
-       card->tx_chain.head = card->tx_chain.head->next;
-       spin_unlock_irqrestore(&chain->lock, flags);
        return NETDEV_TX_OK;
 }
 
@@ -893,16 +892,11 @@ spider_net_xmit(struct sk_buff *skb, struct net_device *netdev)
 static void
 spider_net_cleanup_tx_ring(struct spider_net_card *card)
 {
-       unsigned long flags;
-
-       spin_lock_irqsave(&card->tx_chain.lock, flags);
-
        if ((spider_net_release_tx_chain(card, 0) != 0) &&
            (card->netdev->flags & IFF_UP)) {
                spider_net_kick_tx_dma(card);
                netif_wake_queue(card->netdev);
        }
-       spin_unlock_irqrestore(&card->tx_chain.lock, flags);
 }
 
 /**
@@ -1930,10 +1924,7 @@ spider_net_stop(struct net_device *netdev)
        spider_net_disable_rxdmac(card);
 
        /* release chains */
-       if (spin_trylock(&card->tx_chain.lock)) {
-               spider_net_release_tx_chain(card, 1);
-               spin_unlock(&card->tx_chain.lock);
-       }
+       spider_net_release_tx_chain(card, 1);
 
        spider_net_free_chain(card, &card->tx_chain);
        spider_net_free_chain(card, &card->rx_chain);