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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: Linas Vepstas <linas@austin.ibm.com>
Cc: James K Lewis <jklewis@us.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
This commit is contained in:
Linas Vepstas 2006-10-10 16:18:18 -05:00 committed by Jeff Garzik
parent 499eea1872
commit a664ccf430
1 changed files with 13 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
drivers/net/spider_net.c
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@ -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 @@ out:
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;
@ -873,8 +879,9 @@ spider_net_xmit(struct sk_buff *skb, struct net_device *netdev)
return NETDEV_TX_BUSY;
}
spider_net_set_low_watermark(card);
spider_net_kick_tx_dma(card);
cnt = spider_net_set_low_watermark(card);
if (cnt < 5)
spider_net_kick_tx_dma(card);
return NETDEV_TX_OK;
}