[PATCH 3/4]: Spidernet transmit interupt mitigation

[Linas Vepstas]

For small packets, the transmit interrupt settings were 
accidentally generating too many interrupts. This patch
turns off all transmit-related interrupts when the tx
queue is mostly empty.

Signed-off-by: Linas Vepstas <linas at austin.ibm.com>
Cc: James K Lewis <jklewis at us.ibm.com>
Cc: Arnd Bergmann <arnd at arndb.de>

----
 drivers/net/spider_net.c |    8 +++++---
 drivers/net/spider_net.h |    7 +++----
 2 files changed, 8 insertions(+), 7 deletions(-)

Index: linux-2.6.18-mm2/drivers/net/spider_net.c
===================================================================
--- linux-2.6.18-mm2.orig/drivers/net/spider_net.c	2006-10-02 19:06:55.000000000 -0500
+++ linux-2.6.18-mm2/drivers/net/spider_net.c	2006-10-02 19:09:38.000000000 -0500
@@ -707,7 +707,9 @@ spider_net_set_low_watermark(struct spid
 		descr = descr->next;
 		cnt++;
 	}
-	if (cnt == 0)
+
+	/* If TX queue is short, don't even bother with interrupts */
+	if (cnt < tx_descriptors/4)
 		return;
 
 	/* Set low-watermark 3/4th's of the way into the queue. */
@@ -716,7 +718,7 @@ spider_net_set_low_watermark(struct spid
 	for (i=0;i<cnt; i++)
 		descr = descr->next;
 
-	/* Set the new watermark, clear the old wtermark */
+	/* 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)
@@ -1639,7 +1641,7 @@ spider_net_enable_card(struct spider_net
 			     SPIDER_NET_INT2_MASK_VALUE);
 
 	spider_net_write_reg(card, SPIDER_NET_GDTDMACCNTR,
-			     SPIDER_NET_GDTBSTA);
+			     SPIDER_NET_GDTBSTA | SPIDER_NET_GDTDCEIDIS);
 }
 
 /**
Index: linux-2.6.18-mm2/drivers/net/spider_net.h
===================================================================
--- linux-2.6.18-mm2.orig/drivers/net/spider_net.h	2006-10-02 19:06:55.000000000 -0500
+++ linux-2.6.18-mm2/drivers/net/spider_net.h	2006-10-02 19:09:38.000000000 -0500
@@ -217,7 +217,8 @@ extern char spider_net_driver_name[];
 #define SPIDER_NET_GDTBSTA             0x00000300
 #define SPIDER_NET_GDTDCEIDIS          0x00000002
 #define SPIDER_NET_DMA_TX_VALUE        SPIDER_NET_TX_DMA_EN | \
-                                       SPIDER_NET_GDTBSTA
+                                       SPIDER_NET_GDTBSTA   | \
+                                       SPIDER_NET_GDTDCEIDIS
 #define SPIDER_NET_DMA_TX_FEND_VALUE	0x00030003
 
 /* SPIDER_NET_UA_DESCR_VALUE is OR'ed with the unicast address */
@@ -326,9 +327,7 @@ enum spider_net_int2_status {
 	SPIDER_NET_GRISPDNGINT
 };
 
-#define SPIDER_NET_TXINT	( (1 << SPIDER_NET_GTTEDINT) | \
-				  (1 << SPIDER_NET_GDTDCEINT) | \
-				  (1 << SPIDER_NET_GDTFDCINT) )
+#define SPIDER_NET_TXINT	( (1 << SPIDER_NET_GDTFDCINT) )
 
 /* we rely on flagged descriptor interrupts*/
 #define SPIDER_NET_RXINT	( (1 << SPIDER_NET_GDAFDCINT) | \