Hi Andrew,

Thank you for the review. Comments inline.

On Wed, 1 Mar 2017 21:22:14 +0300, Andrew Rybchenko [off-list ref] wrote:

On 03/01/2017 08:19 PM, Olivier Matz wrote:

quoted

Introduce a new API to get the status of a descriptor.

For Rx, it is almost similar to rx_descriptor_done API, except it
differentiates "used" descriptors (which are hold by the driver and not
returned to the hardware).

For Tx, it is a new API.

The descriptor_done() API, and probably the rx_queue_count() API could
be replaced by this new API as soon as it is implemented on all PMDs.

Signed-off-by: Olivier Matz <redacted>
---
  lib/librte_ether/rte_ethdev.h | 86 +++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 86 insertions(+)

diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
index 97f3e2d..9ac9c61 100644
--- a/lib/librte_ether/rte_ethdev.h
+++ b/lib/librte_ether/rte_ethdev.h

@@ -1179,6 +1179,14 @@ typedef uint32_t (*eth_rx_queue_count_t)(struct rte_eth_dev *dev,
  typedef int (*eth_rx_descriptor_done_t)(void *rxq, uint16_t offset);
  /**< @internal Check DD bit of specific RX descriptor */
  
+typedef int (*eth_rx_descriptor_status_t)(struct rte_eth_dev *dev,
+	uint16_t rx_queue_id, uint16_t offset);
+/**< @internal Check the status of a Rx descriptor */
+
+typedef int (*eth_tx_descriptor_status_t)(struct rte_eth_dev *dev,
+	uint16_t tx_queue_id, uint16_t offset);
+/**< @internal Check the status of a Tx descriptor */
+
  typedef int (*eth_fw_version_get_t)(struct rte_eth_dev *dev,
  				     char *fw_version, size_t fw_size);
  /**< @internal Get firmware information of an Ethernet device. */

@@ -1483,6 +1491,10 @@ struct eth_dev_ops {
  	eth_queue_release_t        rx_queue_release; /**< Release RX queue. */
  	eth_rx_queue_count_t       rx_queue_count;/**< Get Rx queue count. */
  	eth_rx_descriptor_done_t   rx_descriptor_done; /**< Check rxd DD bit. */
+	eth_rx_descriptor_status_t rx_descriptor_status;
+	/**< Check the status of a Rx descriptor. */
+	eth_tx_descriptor_status_t tx_descriptor_status;
+	/**< Check the status of a Tx descriptor. */
  	eth_rx_enable_intr_t       rx_queue_intr_enable;  /**< Enable Rx queue interrupt. */
  	eth_rx_disable_intr_t      rx_queue_intr_disable; /**< Disable Rx queue interrupt. */
  	eth_tx_queue_setup_t       tx_queue_setup;/**< Set up device TX queue. */

@@ -2768,6 +2780,80 @@ rte_eth_rx_descriptor_done(uint8_t port_id, uint16_t queue_id, uint16_t offset)
  		dev->data->rx_queues[queue_id], offset);
  }
  
+#define RTE_ETH_RX_DESC_AVAIL 0 /**< Desc available for hw. */
+#define RTE_ETH_RX_DESC_DONE  1 /**< Desc done, filled by hw. */
+#define RTE_ETH_RX_DESC_USED  2 /**< Desc used by driver. */
+
+/**
+ * Check the status of a Rx descriptor in the queue  

I think it would be useful to highlight caller context.
Should it be the same CPU which receives packets from the queue?

Yes, you are right it would be useful. I suggest the following sentences:

  This function should be called on a dataplane core like the
  Rx function. They should not be called concurrently on the same
  queue.

quoted

+ *
+ * @param port_id
+ *  The port identifier of the Ethernet device.
+ * @param queue_id
+ *  The Rx queue identifier on this port.
+ * @param offset
+ *  The offset of the descriptor starting from tail (0 is the next
+ *  packet to be received by the driver).
+ * @return
+ *  - (RTE_ETH_DESC_AVAIL): Descriptor is available for the hardware to
+ *    receive a packet.
+ *  - (RTE_ETH_DESC_DONE): Descriptor is done, it is filled by hw, but
+ *    not yet processed by the driver (i.e. in the receive queue).
+ *  - (RTE_ETH_DESC_USED): Descriptor is unavailable (hold by driver,
+ *    not yet returned to hw).  

It looks like it is the most suitable for descriptors which are reserved 
and never used.

Can you give some more details about what is a reserved but never
used descriptor? (same question for Tx)

quoted

+ *  - (-ENODEV) if *port_id* invalid.
+ *  - (-EINVAL) bad descriptor offset.
+ *  - (-ENOTSUP) if the device does not support this function.  

What should be returned if queue_id is invalid?

I'd say -ENODEV too. On the other hand, adding these checks is
maybe not a good idea as we are in dataplane.

The previous API rx_descriptor_done() API was taking the queue
pointer as parameter, like Rx/Tx functions. It's probably a better
idea.

What should be returned if the queue is stopped?

For the same performance reasons, I think we should just highlight
in the API that this dataplane function should not be called on a
stopped queue.

quoted

+ */
+static inline int
+rte_eth_rx_descriptor_status(uint8_t port_id, uint16_t queue_id,
+	uint16_t offset)
+{
+	struct rte_eth_dev *dev;
+
+	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
+	dev = &rte_eth_devices[port_id];
+	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->rx_descriptor_status, -ENOTSUP);
+  

May be it makes sense to range check queue_id here to avoid such code in 
each PMD?

If we keep this API, yes. If we switch to a queue pointer as proposed
above, we will assume (and highlight in the API doc) that the pointer
must be valid, like for Rx/Tx funcs.


Olivier