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mv643xx_eth: get rid of receive-side locking
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By having the receive out-of-memory handling timer schedule the napi
poll handler and then doing oom processing from the napi poll handler,
all code that touches receive state moves to napi context, letting us
get rid of all explicit locking in the receive paths since the only
mutual exclusion we need anymore at that point is protection against
reentering ourselves, which is provided by napi synchronisation.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
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Lennert Buytenhek authored and Lennert Buytenhek committed Sep 5, 2008
1 parent 78fff83 commit 2257e05
Showing 1 changed file with 68 additions and 64 deletions.
132 changes: 68 additions & 64 deletions drivers/net/mv643xx_eth.c
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Original file line number Diff line number Diff line change
Expand Up @@ -329,8 +329,6 @@ struct rx_queue {
dma_addr_t rx_desc_dma;
int rx_desc_area_size;
struct sk_buff **rx_skb;

struct timer_list rx_oom;
};

struct tx_queue {
Expand Down Expand Up @@ -372,6 +370,7 @@ struct mv643xx_eth_private {
u8 rxq_mask;
int rxq_primary;
struct napi_struct napi;
struct timer_list rx_oom;
struct rx_queue rxq[8];

/*
Expand Down Expand Up @@ -473,44 +472,43 @@ static void __txq_maybe_wake(struct tx_queue *txq)
/* rx ***********************************************************************/
static void txq_reclaim(struct tx_queue *txq, int force);

static void rxq_refill(struct rx_queue *rxq)
static int rxq_refill(struct rx_queue *rxq, int budget, int *oom)
{
struct mv643xx_eth_private *mp = rxq_to_mp(rxq);
unsigned long flags;
int skb_size;
int refilled;

spin_lock_irqsave(&mp->lock, flags);
/*
* Reserve 2+14 bytes for an ethernet header (the hardware
* automatically prepends 2 bytes of dummy data to each
* received packet), 16 bytes for up to four VLAN tags, and
* 4 bytes for the trailing FCS -- 36 bytes total.
*/
skb_size = rxq_to_mp(rxq)->dev->mtu + 36;

/*
* Make sure that the skb size is a multiple of 8 bytes, as
* the lower three bits of the receive descriptor's buffer
* size field are ignored by the hardware.
*/
skb_size = (skb_size + 7) & ~7;

while (rxq->rx_desc_count < rxq->rx_ring_size) {
int skb_size;
refilled = 0;
while (refilled < budget && rxq->rx_desc_count < rxq->rx_ring_size) {
struct sk_buff *skb;
int unaligned;
int rx;

/*
* Reserve 2+14 bytes for an ethernet header (the
* hardware automatically prepends 2 bytes of dummy
* data to each received packet), 16 bytes for up to
* four VLAN tags, and 4 bytes for the trailing FCS
* -- 36 bytes total.
*/
skb_size = mp->dev->mtu + 36;

/*
* Make sure that the skb size is a multiple of 8
* bytes, as the lower three bits of the receive
* descriptor's buffer size field are ignored by
* the hardware.
*/
skb_size = (skb_size + 7) & ~7;

skb = dev_alloc_skb(skb_size + dma_get_cache_alignment() - 1);
if (skb == NULL)
if (skb == NULL) {
*oom = 1;
break;
}

unaligned = (u32)skb->data & (dma_get_cache_alignment() - 1);
if (unaligned)
skb_reserve(skb, dma_get_cache_alignment() - unaligned);

refilled++;
rxq->rx_desc_count++;

rx = rxq->rx_used_desc++;
Expand All @@ -534,15 +532,7 @@ static void rxq_refill(struct rx_queue *rxq)
skb_reserve(skb, 2);
}

if (rxq->rx_desc_count != rxq->rx_ring_size)
mod_timer(&rxq->rx_oom, jiffies + (HZ / 10));

spin_unlock_irqrestore(&mp->lock, flags);
}

static inline void rxq_refill_timer_wrapper(unsigned long data)
{
rxq_refill((struct rx_queue *)data);
return refilled;
}

static int rxq_process(struct rx_queue *rxq, int budget)
Expand All @@ -556,17 +546,12 @@ static int rxq_process(struct rx_queue *rxq, int budget)
struct rx_desc *rx_desc;
unsigned int cmd_sts;
struct sk_buff *skb;
unsigned long flags;

spin_lock_irqsave(&mp->lock, flags);

rx_desc = &rxq->rx_desc_area[rxq->rx_curr_desc];

cmd_sts = rx_desc->cmd_sts;
if (cmd_sts & BUFFER_OWNED_BY_DMA) {
spin_unlock_irqrestore(&mp->lock, flags);
if (cmd_sts & BUFFER_OWNED_BY_DMA)
break;
}
rmb();

skb = rxq->rx_skb[rxq->rx_curr_desc];
Expand All @@ -576,8 +561,6 @@ static int rxq_process(struct rx_queue *rxq, int budget)
if (rxq->rx_curr_desc == rxq->rx_ring_size)
rxq->rx_curr_desc = 0;

spin_unlock_irqrestore(&mp->lock, flags);

dma_unmap_single(NULL, rx_desc->buf_ptr,
rx_desc->buf_size, DMA_FROM_DEVICE);
rxq->rx_desc_count--;
Expand Down Expand Up @@ -635,15 +618,14 @@ static int rxq_process(struct rx_queue *rxq, int budget)
mp->dev->last_rx = jiffies;
}

rxq_refill(rxq);

return rx;
}

static int mv643xx_eth_poll(struct napi_struct *napi, int budget)
{
struct mv643xx_eth_private *mp;
int rx;
int work_done;
int oom;
int i;

mp = container_of(napi, struct mv643xx_eth_private, napi);
Expand All @@ -663,17 +645,32 @@ static int mv643xx_eth_poll(struct napi_struct *napi, int budget)
}
#endif

rx = 0;
for (i = 7; rx < budget && i >= 0; i--)
if (mp->rxq_mask & (1 << i))
rx += rxq_process(mp->rxq + i, budget - rx);
work_done = 0;
oom = 0;
for (i = 7; work_done < budget && i >= 0; i--) {
if (mp->rxq_mask & (1 << i)) {
struct rx_queue *rxq = mp->rxq + i;

if (rx < budget) {
work_done += rxq_process(rxq, budget - work_done);
work_done += rxq_refill(rxq, budget - work_done, &oom);
}
}

if (work_done < budget) {
if (oom)
mod_timer(&mp->rx_oom, jiffies + (HZ / 10));
netif_rx_complete(mp->dev, napi);
wrl(mp, INT_MASK(mp->port_num), INT_TX_END | INT_RX | INT_EXT);
}

return rx;
return work_done;
}

static inline void oom_timer_wrapper(unsigned long data)
{
struct mv643xx_eth_private *mp = (void *)data;

napi_schedule(&mp->napi);
}


Expand Down Expand Up @@ -1565,10 +1562,6 @@ static int rxq_init(struct mv643xx_eth_private *mp, int index)
nexti * sizeof(struct rx_desc);
}

init_timer(&rxq->rx_oom);
rxq->rx_oom.data = (unsigned long)rxq;
rxq->rx_oom.function = rxq_refill_timer_wrapper;

return 0;


Expand All @@ -1591,8 +1584,6 @@ static void rxq_deinit(struct rx_queue *rxq)

rxq_disable(rxq);

del_timer_sync(&rxq->rx_oom);

for (i = 0; i < rxq->rx_ring_size; i++) {
if (rxq->rx_skb[i]) {
dev_kfree_skb(rxq->rx_skb[i]);
Expand Down Expand Up @@ -1854,7 +1845,7 @@ static irqreturn_t mv643xx_eth_irq(int irq, void *dev_id)
wrl(mp, INT_MASK(mp->port_num), 0x00000000);
rdl(mp, INT_MASK(mp->port_num));

netif_rx_schedule(dev, &mp->napi);
napi_schedule(&mp->napi);
}

/*
Expand Down Expand Up @@ -2041,6 +2032,7 @@ static int mv643xx_eth_open(struct net_device *dev)
{
struct mv643xx_eth_private *mp = netdev_priv(dev);
int err;
int oom;
int i;

wrl(mp, INT_CAUSE(mp->port_num), 0);
Expand All @@ -2056,6 +2048,9 @@ static int mv643xx_eth_open(struct net_device *dev)

init_mac_tables(mp);

napi_enable(&mp->napi);

oom = 0;
for (i = 0; i < 8; i++) {
if ((mp->rxq_mask & (1 << i)) == 0)
continue;
Expand All @@ -2068,7 +2063,12 @@ static int mv643xx_eth_open(struct net_device *dev)
goto out;
}

rxq_refill(mp->rxq + i);
rxq_refill(mp->rxq + i, INT_MAX, &oom);
}

if (oom) {
mp->rx_oom.expires = jiffies + (HZ / 10);
add_timer(&mp->rx_oom);
}

for (i = 0; i < 8; i++) {
Expand All @@ -2084,8 +2084,6 @@ static int mv643xx_eth_open(struct net_device *dev)
}
}

napi_enable(&mp->napi);

netif_carrier_off(dev);
netif_stop_queue(dev);

Expand Down Expand Up @@ -2150,6 +2148,8 @@ static int mv643xx_eth_stop(struct net_device *dev)

napi_disable(&mp->napi);

del_timer_sync(&mp->rx_oom);

netif_carrier_off(dev);
netif_stop_queue(dev);

Expand Down Expand Up @@ -2613,8 +2613,6 @@ static int mv643xx_eth_probe(struct platform_device *pdev)

mp->dev = dev;

netif_napi_add(dev, &mp->napi, mv643xx_eth_poll, 64);

set_params(mp, pd);

spin_lock_init(&mp->lock);
Expand All @@ -2633,6 +2631,12 @@ static int mv643xx_eth_probe(struct platform_device *pdev)
}
init_pscr(mp, pd->speed, pd->duplex);

netif_napi_add(dev, &mp->napi, mv643xx_eth_poll, 128);

init_timer(&mp->rx_oom);
mp->rx_oom.data = (unsigned long)mp;
mp->rx_oom.function = oom_timer_wrapper;


res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
BUG_ON(!res);
Expand Down

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