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ethoc: remove division from loops

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Calculating the BD entry using a modulus operation isn't optimal, especially
inside the loop.  This patch removes the modulus operations in favour of:

i)  simply checking for wrapping in the case of cur_rx
ii) forcing num_tx to be a power of two and using it to mask out the
    entry from cur_tx

The also prevents possible issues related overflow of the cur_rx and cur_tx
counters.

Signed-off-by: Jonas Bonn <jonas@southpole.se>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jonas Bonn 2010-11-25 02:30:32 +00:00 committed by David S. Miller
parent 4f64bcb2fc
commit 6a632625c7
1 changed files with 13 additions and 4 deletions
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17
drivers/net/ethoc.c
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@ -412,7 +412,7 @@ static int ethoc_rx(struct net_device *dev, int limit)
unsigned int entry;
struct ethoc_bd bd;
entry = priv->num_tx + (priv->cur_rx % priv->num_rx);
entry = priv->num_tx + priv->cur_rx;
ethoc_read_bd(priv, entry, &bd);
if (bd.stat & RX_BD_EMPTY) {
ethoc_ack_irq(priv, INT_MASK_RX);
@ -456,7 +456,8 @@ static int ethoc_rx(struct net_device *dev, int limit)
bd.stat &= ~RX_BD_STATS;
bd.stat |= RX_BD_EMPTY;
ethoc_write_bd(priv, entry, &bd);
priv->cur_rx++;
if (++priv->cur_rx == priv->num_rx)
priv->cur_rx = 0;
}
return count;
@ -503,7 +504,7 @@ static int ethoc_tx(struct net_device *dev, int limit)
for (count = 0; count < limit; ++count) {
unsigned int entry;
entry = priv->dty_tx % priv->num_tx;
entry = priv->dty_tx & (priv->num_tx-1);
ethoc_read_bd(priv, entry, &bd);
@ -1000,9 +1001,17 @@ static int __devinit ethoc_probe(struct platform_device *pdev)
/* calculate the number of TX/RX buffers, maximum 128 supported */
num_bd = min_t(unsigned int,
128, (netdev->mem_end - netdev->mem_start + 1) / ETHOC_BUFSIZ);
priv->num_tx = max(2, num_bd / 4);
if (num_bd < 4) {
ret = -ENODEV;
goto error;
}
/* num_tx must be a power of two */
priv->num_tx = rounddown_pow_of_two(num_bd >> 1);
priv->num_rx = num_bd - priv->num_tx;
dev_dbg(&pdev->dev, "ethoc: num_tx: %d num_rx: %d\n",
priv->num_tx, priv->num_rx);
priv->vma = devm_kzalloc(&pdev->dev, num_bd*sizeof(void*), GFP_KERNEL);
if (!priv->vma) {
ret = -ENOMEM;