diff options
| author | Linas Vepstas <linas@austin.ibm.com> | 2006-10-10 16:18:18 -0500 |
|---|---|---|
| committer | Jeff Garzik <jeff@garzik.org> | 2006-10-11 04:04:26 -0400 |
| commit | a664ccf430547696951bf3949f5a2de5079ece5a (patch) | |
| tree | 53fc9fdba563fe8f70c9a3de51b78c52de84fe23 /drivers/net/spider_net.c | |
| parent | 499eea18722e43f0ee15e11ac16ffcbd10b70b24 (diff) | |
| download | lwn-a664ccf430547696951bf3949f5a2de5079ece5a.tar.gz lwn-a664ccf430547696951bf3949f5a2de5079ece5a.zip | |
[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>
Diffstat (limited to 'drivers/net/spider_net.c')
| -rw-r--r-- | drivers/net/spider_net.c | 19 |
1 files changed, 13 insertions, 6 deletions
diff --git a/drivers/net/spider_net.c b/drivers/net/spider_net.c index 6bb8f1f9437c..caa11c6f21b9 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; } |