[dpdk-dev] [PATCH] ethdev: fix checking for tx_free_thresh

[Zoltan Kiss]

This parameter is not consistent between the drivers: some use it as
rte_eth_tx_burst() requires, some release buffers when the number of free
descriptors drop below this value.
Let's use it as most fast-path code does, which is the latter, and update
comments throughout the code to reflect that.

Signed-off-by: Zoltan Kiss <zoltan.kiss at linaro.org>
---
 drivers/net/e1000/em_rxtx.c      |  7 ++++---
 drivers/net/fm10k/fm10k.h        |  1 -
 drivers/net/fm10k/fm10k_ethdev.c |  1 -
 drivers/net/fm10k/fm10k_rxtx.c   |  2 +-
 drivers/net/i40e/i40e_rxtx.c     |  2 +-
 drivers/net/i40e/i40e_rxtx.h     |  5 +++--
 drivers/net/ixgbe/ixgbe_rxtx.c   |  3 +--
 drivers/net/ixgbe/ixgbe_rxtx.h   |  4 +++-
 drivers/net/virtio/virtio_rxtx.c |  2 +-
 lib/librte_ether/rte_ethdev.h    | 11 ++++++-----
 10 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/net/e1000/em_rxtx.c b/drivers/net/e1000/em_rxtx.c
index fdc825f..38f5c3b 100644
--- a/drivers/net/e1000/em_rxtx.c
+++ b/drivers/net/e1000/em_rxtx.c
@@ -182,7 +182,9 @@ struct em_tx_queue {
 	volatile uint32_t      *tdt_reg_addr; /**< Address of TDT register. */
 	uint16_t               nb_tx_desc;    /**< number of TX descriptors. */
 	uint16_t               tx_tail;  /**< Current value of TDT register. */
-	uint16_t               tx_free_thresh;/**< minimum TX before freeing. */
+	/**< Start freeing TX buffers if there are less free descriptors than
+	     this value. */
+	uint16_t               tx_free_thresh;
 	/**< Number of TX descriptors to use before RS bit is set. */
 	uint16_t               tx_rs_thresh;
 	/** Number of TX descriptors used since RS bit was set. */
@@ -418,9 +420,8 @@ eth_em_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 	txe = &sw_ring[tx_id];
 
 	/* Determine if the descriptor ring needs to be cleaned. */
-	if ((txq->nb_tx_desc - txq->nb_tx_free) > txq->tx_free_thresh) {
+	 if (txq->nb_tx_free < txq->tx_free_thresh)
 		em_xmit_cleanup(txq);
-	}
 
 	/* TX loop */
 	for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
diff --git a/drivers/net/fm10k/fm10k.h b/drivers/net/fm10k/fm10k.h
index 1b542c5..c089882 100644
--- a/drivers/net/fm10k/fm10k.h
+++ b/drivers/net/fm10k/fm10k.h
@@ -200,7 +200,6 @@ struct fm10k_tx_queue {
 	uint16_t next_free;
 	uint16_t nb_free;
 	uint16_t nb_used;
-	uint16_t free_trigger;
 	uint16_t free_thresh;
 	uint16_t rs_thresh;
 	volatile uint32_t *tail_ptr;
diff --git a/drivers/net/fm10k/fm10k_ethdev.c b/drivers/net/fm10k/fm10k_ethdev.c
index 406c350..f031f8f 100644
--- a/drivers/net/fm10k/fm10k_ethdev.c
+++ b/drivers/net/fm10k/fm10k_ethdev.c
@@ -203,7 +203,6 @@ tx_queue_reset(struct fm10k_tx_queue *q)
 	q->next_free = 0;
 	q->nb_used = 0;
 	q->nb_free = q->nb_desc - 1;
-	q->free_trigger = q->nb_free - q->free_thresh;
 	fifo_reset(&q->rs_tracker, (q->nb_desc + 1) / q->rs_thresh);
 	FM10K_PCI_REG_WRITE(q->tail_ptr, 0);
 }
diff --git a/drivers/net/fm10k/fm10k_rxtx.c b/drivers/net/fm10k/fm10k_rxtx.c
index f5d1ad0..7d5e32c 100644
--- a/drivers/net/fm10k/fm10k_rxtx.c
+++ b/drivers/net/fm10k/fm10k_rxtx.c
@@ -450,7 +450,7 @@ fm10k_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 		mb = tx_pkts[count];
 
 		/* running low on descriptors? try to free some... */
-		if (q->nb_free < q->free_trigger)
+		if (q->nb_free < q->free_thresh)
 			tx_free_descriptors(q);
 
 		/* make sure there are enough free descriptors to transmit the
diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c
index 2de0ac4..fcacd34 100644
--- a/drivers/net/i40e/i40e_rxtx.c
+++ b/drivers/net/i40e/i40e_rxtx.c
@@ -1236,7 +1236,7 @@ i40e_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 	txe = &sw_ring[tx_id];
 
 	/* Check if the descriptor ring needs to be cleaned. */
-	if ((txq->nb_tx_desc - txq->nb_tx_free) > txq->tx_free_thresh)
+	if (txq->nb_tx_free < txq->tx_free_thresh)
 		i40e_xmit_cleanup(txq);
 
 	for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
diff --git a/drivers/net/i40e/i40e_rxtx.h b/drivers/net/i40e/i40e_rxtx.h
index decbc3d..87222e6 100644
--- a/drivers/net/i40e/i40e_rxtx.h
+++ b/drivers/net/i40e/i40e_rxtx.h
@@ -136,8 +136,9 @@ struct i40e_tx_queue {
 	uint16_t last_desc_cleaned;
 	/**< Total number of TX descriptors ready to be allocated. */
 	uint16_t nb_tx_free;
-	/**< Number of TX descriptors to use before RS bit is set. */
-	uint16_t tx_free_thresh; /**< minimum TX before freeing. */
+	/**< Start freeing TX buffers if there are less free descriptors than
+	     this value. */
+	uint16_t tx_free_thresh;
 	/** Number of TX descriptors to use before RS bit is set. */
 	uint16_t tx_rs_thresh;
 	uint8_t pthresh; /**< Prefetch threshold register. */
diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 3ace8a8..31730e2 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx.c
@@ -593,9 +593,8 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 	txe = &sw_ring[tx_id];
 
 	/* Determine if the descriptor ring needs to be cleaned. */
-	if ((txq->nb_tx_desc - txq->nb_tx_free) > txq->tx_free_thresh) {
+	if (txq->nb_tx_free < txq->tx_free_thresh)
 		ixgbe_xmit_cleanup(txq);
-	}
 
 	rte_prefetch0(&txe->mbuf->pool);
 
diff --git a/drivers/net/ixgbe/ixgbe_rxtx.h b/drivers/net/ixgbe/ixgbe_rxtx.h
index af36438..0e6ad93 100644
--- a/drivers/net/ixgbe/ixgbe_rxtx.h
+++ b/drivers/net/ixgbe/ixgbe_rxtx.h
@@ -195,7 +195,9 @@ struct ixgbe_tx_queue {
 	volatile uint32_t   *tdt_reg_addr; /**< Address of TDT register. */
 	uint16_t            nb_tx_desc;    /**< number of TX descriptors. */
 	uint16_t            tx_tail;       /**< current value of TDT reg. */
-	uint16_t            tx_free_thresh;/**< minimum TX before freeing. */
+	/**< Start freeing TX buffers if there are less free descriptors than
+	     this value. */
+	uint16_t            tx_free_thresh;
 	/** Number of TX descriptors to use before RS bit is set. */
 	uint16_t            tx_rs_thresh;
 	/** Number of TX descriptors used since RS bit was set. */
diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index 3ff275c..091c7fb 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -744,7 +744,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 	nb_used = VIRTQUEUE_NUSED(txvq);
 
 	virtio_rmb();
-	if (likely(nb_used > txvq->vq_free_thresh))
+	if (likely(nb_used > txvq->vq_nentries - txvq->vq_free_thresh))
 		virtio_xmit_cleanup(txvq, nb_used);
 
 	nb_tx = 0;
diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
index f1219ac..d1e2f2a 100644
--- a/lib/librte_ether/rte_ethdev.h
+++ b/lib/librte_ether/rte_ethdev.h
@@ -632,7 +632,9 @@ struct rte_eth_rxconf {
 struct rte_eth_txconf {
 	struct rte_eth_thresh tx_thresh; /**< TX ring threshold registers. */
 	uint16_t tx_rs_thresh; /**< Drives the setting of RS bit on TXDs. */
-	uint16_t tx_free_thresh; /**< Drives the freeing of TX buffers. */
+	uint16_t tx_free_thresh; /**< Start freeing TX buffers if there are
+				      less free descriptors than this value. */
+
 	uint32_t txq_flags; /**< Set flags for the Tx queue */
 	uint8_t tx_deferred_start; /**< Do not start queue with rte_eth_dev_start(). */
 };
@@ -2534,10 +2536,9 @@ rte_eth_rx_descriptor_done(uint8_t port_id, uint16_t queue_id, uint16_t offset)
  * transparently free the memory buffers of packets previously sent.
  * This feature is driven by the *tx_free_thresh* value supplied to the
  * rte_eth_dev_configure() function at device configuration time.
- * When the number of previously sent packets reached the "minimum transmit
- * packets to free" threshold, the rte_eth_tx_burst() function must
- * [attempt to] free the *rte_mbuf*  buffers of those packets whose
- * transmission was effectively completed.
+ * When the number of free TX descriptors drops below this threshold, the
+ * rte_eth_tx_burst() function must [attempt to] free the *rte_mbuf*  buffers
+ * of those packets whose transmission was effectively completed.
  *
  * @param port_id
  *   The port identifier of the Ethernet device.
-- 
1.9.1