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authorLinas Vepstas <linas@austin.ibm.com>2006-10-10 16:18:18 -0500
committerJeff Garzik <jeff@garzik.org>2006-10-11 04:04:26 -0400
commita664ccf430547696951bf3949f5a2de5079ece5a (patch)
tree53fc9fdba563fe8f70c9a3de51b78c52de84fe23
parent499eea18722e43f0ee15e11ac16ffcbd10b70b24 (diff)
[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>
-rw-r--r--drivers/net/spider_net.c19
1 files changed, 13 insertions, 6 deletions
diff --git a/drivers/net/spider_net.c b/drivers/net/spider_net.c
index 6bb8f1f9437..caa11c6f21b 100644
--- a/drivers/net/spider_net.c
+++ b/drivers/net/spider_net.c
@@ -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;
}