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Subject[PATCH 6/6]: powerpc/cell spidernet refine locking
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The transmit side of the spider ethernet driver currently
places locks around some very large chunks of code. This
results in a fair amount of lock contention is some cases.
This patch makes the locks much more fine-grained, protecting
only the cirtical sections. One lock is used to protect
three locations: the queue head and tail pointers, and the
queue low-watermark location.

This, with the previous patches, result in the following
performance, using netperf, averaged over 5 minute runs:

pkt size rate
-------- ----
1500 804 Mbits/sec
800 701 Mbits/sec
600 600 Mbits/sec
300 280 Mbits/sec
60 60 Mbits/sec

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Cc: Utz Bacher <utz.bacher@de.ibm.com>
Cc: Jens Osterkamp <Jens.Osterkamp@de.ibm.com>
Cc: James K Lewis <jklewis@us.ibm.com>

----
drivers/net/spider_net.c | 77 ++++++++++++++++++++---------------------------
drivers/net/spider_net.h | 2 -
2 files changed, 35 insertions(+), 44 deletions(-)
Index: linux-2.6.18-rc3-mm2/drivers/net/spider_net.c
===================================================================
--- linux-2.6.18-rc3-mm2.orig/drivers/net/spider_net.c 2006-08-15 14:28:56.000000000 -0500
+++ linux-2.6.18-rc3-mm2/drivers/net/spider_net.c 2006-08-15 14:29:36.000000000 -0500
@@ -644,8 +644,9 @@ static int
spider_net_prepare_tx_descr(struct spider_net_card *card,
struct sk_buff *skb)
{
- struct spider_net_descr *descr = card->tx_chain.head;
+ struct spider_net_descr *descr;
dma_addr_t buf;
+ unsigned long flags;

buf = pci_map_single(card->pdev, skb->data, skb->len, PCI_DMA_TODEVICE);
if (buf == DMA_ERROR_CODE) {
@@ -655,6 +656,10 @@ spider_net_prepare_tx_descr(struct spide
return -ENOMEM;
}

+ spin_lock_irqsave(&card->tx_chain.lock, flags);
+ descr = card->tx_chain.head;
+ card->tx_chain.head = card->tx_chain.head->next;
+
descr->buf_addr = buf;
descr->buf_size = skb->len;
descr->next_descr_addr = 0;
@@ -663,6 +668,8 @@ spider_net_prepare_tx_descr(struct spide

descr->dmac_cmd_status =
SPIDER_NET_DESCR_CARDOWNED | SPIDER_NET_DMAC_NOCS;
+ spin_unlock_irqrestore(&card->tx_chain.lock, flags);
+
if (skb->protocol == htons(ETH_P_IP))
switch (skb->nh.iph->protocol) {
case IPPROTO_TCP:
@@ -673,37 +680,16 @@ spider_net_prepare_tx_descr(struct spide
break;
}

+ /* Chain the bus address, so that the DMA engine finds this descr. */
descr->prev->next_descr_addr = descr->bus_addr;

return 0;
}

-/**
- * spider_net_release_tx_descr - processes a used tx descriptor
- * @card: card structure
- * @descr: descriptor to release
- *
- * releases a used tx descriptor (unmapping, freeing of skb)
- */
-static inline void
-spider_net_release_tx_descr(struct spider_net_card *card)
-{
- struct spider_net_descr *descr = card->tx_chain.tail;
- struct sk_buff *skb;
-
- card->tx_chain.tail = card->tx_chain.tail->next;
- descr->dmac_cmd_status |= SPIDER_NET_DESCR_NOT_IN_USE;
-
- /* unmap the skb */
- skb = descr->skb;
- pci_unmap_single(card->pdev, descr->buf_addr, skb->len,
- PCI_DMA_TODEVICE);
- dev_kfree_skb_any(skb);
-}
-
static void
spider_net_set_low_watermark(struct spider_net_card *card)
{
+ unsigned long flags;
int status;
int cnt=0;
int i;
@@ -727,11 +713,13 @@ spider_net_set_low_watermark(struct spid
descr = descr->next;

/* Set the new watermark, clear the old wtermark */
+ spin_lock_irqsave(&card->tx_chain.lock, flags);
descr->dmac_cmd_status |= SPIDER_NET_DESCR_TXDESFLG;
if (card->low_watermark && card->low_watermark != descr)
card->low_watermark->dmac_cmd_status =
card->low_watermark->dmac_cmd_status & ~SPIDER_NET_DESCR_TXDESFLG;
card->low_watermark = descr;
+ spin_unlock_irqrestore(&card->tx_chain.lock, flags);
}

/**
@@ -750,22 +738,30 @@ static int
spider_net_release_tx_chain(struct spider_net_card *card, int brutal)
{
struct spider_net_descr_chain *chain = &card->tx_chain;
+ struct spider_net_descr *descr;
+ struct sk_buff *skb;
+ u32 buf_addr;
+ unsigned long flags;
int status;
int rc=0;

spider_net_read_reg(card, SPIDER_NET_GDTDMACCNTR);

while (chain->tail != chain->head) {
- status = spider_net_get_descr_status(chain->tail);
+ spin_lock_irqsave(&chain->lock, flags);
+ descr = chain->tail;
+
+ status = spider_net_get_descr_status(descr);
switch (status) {
case SPIDER_NET_DESCR_COMPLETE:
card->netdev_stats.tx_packets++;
- card->netdev_stats.tx_bytes += chain->tail->skb->len;
+ card->netdev_stats.tx_bytes += descr->skb->len;
break;

case SPIDER_NET_DESCR_CARDOWNED:
if (!brutal) {
rc = 1;
+ spin_unlock_irqrestore(&chain->lock, flags);
goto done;
}
/* fallthrough, if we release the descriptors
@@ -785,9 +781,19 @@ spider_net_release_tx_chain(struct spide
default:
card->netdev_stats.tx_dropped++;
rc = 1;
+ spin_unlock_irqrestore(&chain->lock, flags);
goto done;
}
- spider_net_release_tx_descr(card);
+
+ chain->tail = chain->tail->next;
+ descr->dmac_cmd_status |= SPIDER_NET_DESCR_NOT_IN_USE;
+ skb = descr->skb;
+ buf_addr = descr->buf_addr;
+ spin_unlock_irqrestore(&chain->lock, flags);
+
+ /* unmap the skb */
+ pci_unmap_single(card->pdev, buf_addr, skb->len, PCI_DMA_TODEVICE);
+ dev_kfree_skb_any(skb);
}
done:
if (rc == 1)
@@ -844,11 +850,8 @@ spider_net_xmit(struct sk_buff *skb, str
struct spider_net_card *card = netdev_priv(netdev);
struct spider_net_descr_chain *chain = &card->tx_chain;
struct spider_net_descr *descr = chain->head;
- unsigned long flags;
int result;

- spin_lock_irqsave(&chain->lock, flags);
-
spider_net_release_tx_chain(card, 0);

if (chain->head->next == chain->tail->prev) {
@@ -869,12 +872,9 @@ spider_net_xmit(struct sk_buff *skb, str
}

result = NETDEV_TX_OK;
-
spider_net_kick_tx_dma(card);
- card->tx_chain.head = card->tx_chain.head->next;

out:
- spin_unlock_irqrestore(&chain->lock, flags);
netif_wake_queue(netdev);
return result;
}
@@ -891,17 +891,11 @@ out:
static void
spider_net_cleanup_tx_ring(struct spider_net_card *card)
{
- unsigned long flags;
-
- spin_lock_irqsave(&card->tx_chain.lock, flags);
-
if ((spider_net_release_tx_chain(card, 0) != 0) &&
(card->netdev->flags & IFF_UP)) {
spider_net_kick_tx_dma(card);
netif_wake_queue(card->netdev);
}
-
- spin_unlock_irqrestore(&card->tx_chain.lock, flags);
}

static void
@@ -1932,10 +1926,7 @@ spider_net_stop(struct net_device *netde
spider_net_disable_rxdmac(card);

/* release chains */
- if (spin_trylock(&card->tx_chain.lock)) {
- spider_net_release_tx_chain(card, 1);
- spin_unlock(&card->tx_chain.lock);
- }
+ spider_net_release_tx_chain(card, 1);

spider_net_free_chain(card, &card->tx_chain);
spider_net_free_chain(card, &card->rx_chain);
Index: linux-2.6.18-rc3-mm2/drivers/net/spider_net.h
===================================================================
--- linux-2.6.18-rc3-mm2.orig/drivers/net/spider_net.h 2006-08-15 14:28:56.000000000 -0500
+++ linux-2.6.18-rc3-mm2/drivers/net/spider_net.h 2006-08-15 14:29:36.000000000 -0500
@@ -24,7 +24,7 @@
#ifndef _SPIDER_NET_H
#define _SPIDER_NET_H

-#define VERSION "1.1 B"
+#define VERSION "1.1 C"

#include "sungem_phy.h"

-
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