[PATCH 3/4]: Spidernet transmit interupt mitigation

Linas Vepstas
2006-10-03T21:03:10Z

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@austin.ibm.com>
Cc: James K Lewis <jklewis@us.ibm.com>
Cc: Arnd Bergmann <arnd@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) | \