[dpdk-dev] [PATCH v5 1/3] ethdev: new API to free consumed buffers in Tx ring

[Billy McFall]

Add a new API to force free consumed buffers on Tx ring. API will return
the number of packets freed (0-n) or error code if feature not supported
(-ENOTSUP) or input invalid (-ENODEV).

Signed-off-by: Billy McFall <bmcfall at redhat.com>
---
 doc/guides/nics/features/default.ini  |  1 +
 doc/guides/prog_guide/mempool_lib.rst | 29 +++++++++++++++++++++++++++++
 lib/librte_ether/rte_ethdev.c         | 14 ++++++++++++++
 lib/librte_ether/rte_ethdev.h         | 31 +++++++++++++++++++++++++++++++
 4 files changed, 75 insertions(+)

diff --git a/doc/guides/nics/features/default.ini b/doc/guides/nics/features/default.ini
index 6e4a043..e2d8c83 100644
--- a/doc/guides/nics/features/default.ini
+++ b/doc/guides/nics/features/default.ini
@@ -55,6 +55,7 @@ FW version           =
 EEPROM dump          =
 Registers dump       =
 Multiprocess aware   =
+Free TX ring buffers =
 BSD nic_uio          =
 Linux UIO            =
 Linux VFIO           =
diff --git a/doc/guides/prog_guide/mempool_lib.rst b/doc/guides/prog_guide/mempool_lib.rst
index ffdc109..92c6fd5 100644
--- a/doc/guides/prog_guide/mempool_lib.rst
+++ b/doc/guides/prog_guide/mempool_lib.rst
@@ -132,6 +132,35 @@ These user-owned caches can be explicitly passed to ``rte_mempool_generic_put()`
 The ``rte_mempool_default_cache()`` call returns the default internal cache if any.
 In contrast to the default caches, user-owned caches can be used by non-EAL threads too.
 
+
+Driver Cache
+~~~~~~~~~~~~
+
+In addition to the a core’s local cache, many of the drivers don't release the mbuf back to the mempool, or local cache,
+immediately after the packet has been transmitted.
+Instead, they leave the mbuf in their txRing and either perform a bulk release when the tx_rs_thresh has been crossed
+or free the mbuf when a slot in the txRing is needed.
+
+An application can request the driver to release used mbufs with the ``rte_eth_tx_done_cleanup()`` API.
+This API requests the driver to release mbufs that are no longer in use, independent of whether or not the tx_rs_thresh
+has been crossed.
+There are two scenarios when an application may want the mbuf back immediately:
+
+* When a given packet needs to be sent to multiple destination interfaces (either for Layer 2 flooding or Layer 3 multi-cast).
+  One option is to make a copy of the packet or a copy of the header portion that needs to manipulated.
+  A second option is to transmit the packet and then poll the ``rte_eth_tx_done_cleanup()`` API until the reference count
+  on the packet is decremented.
+  Then the same packet can be transmitted to the next destination interface.
+
+* If an application is designed to make multiple runs, like a packet generator, and one run has completed.
+  The application may want to reset to a clean state.
+  In this case, it may want to call the ``rte_eth_tx_done_cleanup()`` API to request each destination interface it has been
+  using to release all of its used mbufs.
+
+To determine if a driver supports this API, check for the *Free TX ring buffers* feature in the *Network Interface
+Controller Drivers* document.
+
+
 Mempool Handlers
 ------------------------
 
diff --git a/lib/librte_ether/rte_ethdev.c b/lib/librte_ether/rte_ethdev.c
index 61f44e2..1cbf6d0 100644
--- a/lib/librte_ether/rte_ethdev.c
+++ b/lib/librte_ether/rte_ethdev.c
@@ -1253,6 +1253,20 @@ rte_eth_tx_buffer_set_err_callback(struct rte_eth_dev_tx_buffer *buffer,
 }
 
 int
+rte_eth_tx_done_cleanup(uint8_t port_id, uint16_t queue_id,  uint32_t free_cnt)
+{
+	struct rte_eth_dev *dev = &rte_eth_devices[port_id];
+
+	/* Validate Input Data. Bail if not valid or not supported. */
+	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
+	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->tx_done_cleanup, -ENOTSUP);
+
+	/* Call driver to free pending mbufs. */
+	return (*dev->dev_ops->tx_done_cleanup)(dev->data->tx_queues[queue_id],
+			free_cnt);
+}
+
+int
 rte_eth_tx_buffer_init(struct rte_eth_dev_tx_buffer *buffer, uint16_t size)
 {
 	int ret = 0;
diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
index c17bbda..b23886c 100644
--- a/lib/librte_ether/rte_ethdev.h
+++ b/lib/librte_ether/rte_ethdev.h
@@ -1183,6 +1183,9 @@ 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. */
 
+typedef int (*eth_tx_done_cleanup_t)(void *txq, uint32_t free_cnt);
+/**< @internal Force mbufs to be from TX ring. */
+
 typedef void (*eth_rxq_info_get_t)(struct rte_eth_dev *dev,
 	uint16_t rx_queue_id, struct rte_eth_rxq_info *qinfo);
 
@@ -1487,6 +1490,7 @@ struct eth_dev_ops {
 	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. */
 	eth_queue_release_t        tx_queue_release; /**< Release TX queue. */
+	eth_tx_done_cleanup_t      tx_done_cleanup;/**< Free tx ring mbufs */
 
 	eth_dev_led_on_t           dev_led_on;    /**< Turn on LED. */
 	eth_dev_led_off_t          dev_led_off;   /**< Turn off LED. */
@@ -3091,6 +3095,33 @@ rte_eth_tx_buffer(uint8_t port_id, uint16_t queue_id,
 }
 
 /**
+ * Request the driver to free mbufs currently cached by the driver. The
+ * driver will only free the mbuf if it is no longer in use. It is the
+ * application's responsibity to ensure rte_eth_tx_buffer_flush(..) is
+ * called if needed.
+ *
+ * @param port_id
+ *   The port identifier of the Ethernet device.
+ * @param queue_id
+ *   The index of the transmit queue through which output packets must be
+ *   sent.
+ *   The value must be in the range [0, nb_tx_queue - 1] previously supplied
+ *   to rte_eth_dev_configure().
+ * @param free_cnt
+ *   Maximum number of packets to free. Use 0 to indicate all possible packets
+ *   should be freed. Note that a packet may be using multiple mbufs.
+ * @return
+ *   Failure: < 0
+ *     -ENODEV: Invalid interface
+ *     -ENOTSUP: Driver does not support function
+ *   Success: >= 0
+ *     0-n: Number of packets freed. More packets may still remain in ring that
+ *     are in use.
+ */
+int
+rte_eth_tx_done_cleanup(uint8_t port_id, uint16_t queue_id,  uint32_t free_cnt);
+
+/**
  * Configure a callback for buffered packets which cannot be sent
  *
  * Register a specific callback to be called when an attempt is made to send
-- 
2.9.3