The sample code talks about single-queue devices and uses locks.
Update it to something resembling more modern code.
Make sure we mention use of READ_ONCE() / WRITE_ONCE().
Change the comment which talked about consumer on the xmit side.
AFAIU xmit is the producer and completions are a consumer.
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
---
CC: corbet@xxxxxxx
CC: linux-doc@xxxxxxxxxxxxxxx
---
Documentation/networking/driver.rst | 61 +++++++++++++----------------
1 file changed, 27 insertions(+), 34 deletions(-)
diff --git a/Documentation/networking/driver.rst b/Documentation/networking/driver.rst
index 4071f2c00f8b..4f5dfa9c022e 100644
--- a/Documentation/networking/driver.rst
+++ b/Documentation/networking/driver.rst
@@ -47,30 +47,43 @@ Instead it must maintain the queue properly. For example,
.. code-block:: c
+ static u32 drv_tx_avail(struct drv_ring *dr)
+ {
+ u32 used = READ_ONCE(dr->prod) - READ_ONCE(dr->cons);
+
+ return dr->tx_ring_size - (used & bp->tx_ring_mask);
+ }
+
static netdev_tx_t drv_hard_start_xmit(struct sk_buff *skb,
struct net_device *dev)
{
struct drv *dp = netdev_priv(dev);
+ struct netdev_queue *txq;
+ struct drv_ring *dr;
+ int idx;
+
+ idx = skb_get_queue_mapping(skb);
+ dr = dp->tx_rings[idx];
+ txq = netdev_get_tx_queue(dev, idx);
- lock_tx(dp);
//...
- /* This is a hard error log it. */
- if (TX_BUFFS_AVAIL(dp) <= (skb_shinfo(skb)->nr_frags + 1)) {
+ /* This should be a very rare race - log it. */
+ if (drv_tx_avail(dr) <= skb_shinfo(skb)->nr_frags + 1) {
netif_stop_queue(dev);
- unlock_tx(dp);
- printk(KERN_ERR PFX "%s: BUG! Tx Ring full when queue awake!\n",
- dev->name);
+ netdev_warn(dev, "Tx Ring full when queue awake!\n");
return NETDEV_TX_BUSY;
}
//... queue packet to card ...
- //... update tx consumer index ...
- if (TX_BUFFS_AVAIL(dp) <= (MAX_SKB_FRAGS + 1))
- netif_stop_queue(dev);
+ netdev_tx_sent_queue(txq, skb->len);
+
+ //... update tx producer index using WRITE_ONCE() ...
+
+ if (!netif_txq_maybe_stop(txq, drv_tx_avail(dr),
+ MAX_SKB_FRAGS + 1, 2 * MAX_SKB_FRAGS))
+ dr->stats.stopped++;
- //...
- unlock_tx(dp);
//...
return NETDEV_TX_OK;
}
@@ -79,30 +92,10 @@ Instead it must maintain the queue properly. For example,
.. code-block:: c
- if (netif_queue_stopped(dp->dev) &&
- TX_BUFFS_AVAIL(dp) > (MAX_SKB_FRAGS + 1))
- netif_wake_queue(dp->dev);
-
-For a non-scatter-gather supporting card, the three tests simply become:
-
-.. code-block:: c
-
- /* This is a hard error log it. */
- if (TX_BUFFS_AVAIL(dp) <= 0)
-
-and:
-
-.. code-block:: c
-
- if (TX_BUFFS_AVAIL(dp) == 0)
-
-and:
-
-.. code-block:: c
+ //... update tx consumer index using WRITE_ONCE() ...
- if (netif_queue_stopped(dp->dev) &&
- TX_BUFFS_AVAIL(dp) > 0)
- netif_wake_queue(dp->dev);
+ netif_txq_completed_wake(txq, cmpl_pkts, cmpl_bytes,
+ drv_tx_avail(dr), 2 * MAX_SKB_FRAGS);
Lockless queue stop / wake helper macros
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
2.39.2
