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Commit 9cc7bf7e authored by Linas Vepstas's avatar Linas Vepstas Committed by Jeff Garzik
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[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: default avatarLinas Vepstas <linas@austin.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: James K Lewis <jklewis@us.ibm.com>
Signed-off-by: default avatarJeff Garzik <jeff@garzik.org>
parent 68a8c609

drivers/net/spider_net.c

+43 −52
Original line number Diff line number Diff line
@@ -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_free_chain(card, &card->tx_chain);

	spider_net_free_chain(card, &card->rx_chain);