ethoc: remove division from loops
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>
diff --git a/drivers/net/ethoc.c b/drivers/net/ethoc.c
index 93b50d6..b79d7e1 100644
--- a/drivers/net/ethoc.c
+++ b/drivers/net/ethoc.c
@@ -412,7 +412,7 @@
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 @@
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 @@
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 @@
/* 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;