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Commit a664ccf4 authored by Linas Vepstas's avatar Linas Vepstas Committed by Jeff Garzik
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[PATCH] powerpc/cell spidernet reduce DMA kicking 



The current code attempts to start the TX dma every time a packet
is queued. This is too conservative, and wastes CPU time. This
patch changes behaviour to call the kick-dma function less often,
only when the tx queue is at risk of emptying.

This reduces cpu usage, improves performance.

Signed-off-by: default avatarLinas Vepstas <linas@austin.ibm.com>
Cc: James K Lewis <jklewis@us.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarJeff Garzik <jeff@garzik.org>
parent 499eea18

drivers/net/spider_net.c

+13 −6
Original line number Diff line number Diff line
@@ -698,7 +698,7 @@ spider_net_prepare_tx_descr(struct spider_net_card *card, 
	return 0;

}



static void

static int

spider_net_set_low_watermark(struct spider_net_card *card)

{

	unsigned long flags;
@@ -719,7 +719,7 @@ spider_net_set_low_watermark(struct spider_net_card *card) 


	/* If TX queue is short, don't even bother with interrupts */

	if (cnt < card->tx_desc/4)

		return;

		return cnt;



	/* Set low-watermark 3/4th's of the way into the queue. */

	descr = card->tx_chain.tail;
@@ -735,6 +735,7 @@ spider_net_set_low_watermark(struct spider_net_card *card) 
		     card->low_watermark->dmac_cmd_status & ~SPIDER_NET_DESCR_TXDESFLG;

	card->low_watermark = descr;

	spin_unlock_irqrestore(&card->tx_chain.lock, flags);

	return cnt;

}



/**
@@ -819,8 +820,12 @@ spider_net_release_tx_chain(struct spider_net_card *card, int brutal) 
 * @card: card structure

 * @descr: descriptor address to enable TX processing at

 *

 * spider_net_kick_tx_dma writes the current tx chain head as start address

 * of the tx descriptor chain and enables the transmission DMA engine

 * This routine will start the transmit DMA running if

 * it is not already running. This routine ned only be

 * called when queueing a new packet to an empty tx queue.

 * Writes the current tx chain head as start address

 * of the tx descriptor chain and enables the transmission

 * DMA engine.

 */

static inline void

spider_net_kick_tx_dma(struct spider_net_card *card)
@@ -860,6 +865,7 @@ spider_net_kick_tx_dma(struct spider_net_card *card) 
static int

spider_net_xmit(struct sk_buff *skb, struct net_device *netdev)

{

	int cnt;

	struct spider_net_card *card = netdev_priv(netdev);

	struct spider_net_descr_chain *chain = &card->tx_chain;
@@ -873,7 +879,8 @@ spider_net_xmit(struct sk_buff *skb, struct net_device *netdev) 
		return NETDEV_TX_BUSY;

	}



	spider_net_set_low_watermark(card);

	cnt = spider_net_set_low_watermark(card);

	if (cnt < 5)

		spider_net_kick_tx_dma(card);

	return NETDEV_TX_OK;

}