diff options
| author | Jakub Kicinski <kuba@kernel.org> | 2023-04-11 18:50:36 -0700 |
|---|---|---|
| committer | Paolo Abeni <pabeni@redhat.com> | 2023-04-13 13:30:21 +0200 |
| commit | 50762d9af307b1c466fe0e1441c7923975927d98 (patch) | |
| tree | efaa9e600ea0c3313d01b7904a7996ec5ae993f5 /Documentation/networking/driver.rst | |
| parent | 21cdc87fa9d8e0f0104db5499a16e2be1f53516a (diff) | |
net: docs: update the sample code in driver.rst
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@google.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'Documentation/networking/driver.rst')
| -rw-r--r-- | Documentation/networking/driver.rst | 61 |
1 files 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 @@ for a driver implementing scatter-gather this means: .. 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 @@ And then at the end of your TX reclamation event handling: .. 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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |